jam

--[[

    IMPORTANT: don't use this program. Aside from the fact that it may be broken
    according to some people, ComputerCraft has currently a bug that can deadlock
    the game when a turtle moves next to a disk drive. And that happens a lot with
    JAM. Turtles moving next to a disk drive, I mean. So the chances are actually
    pretty high for this to happen. Trust me, it does happen.

]]

print("Unusable due to a CC bug as it stands (CC 1.56). Remove this code line to use it anyway at your own peril.") return


--[[
    JAM - Just Another Miner - 2013 Sangar

    This program is licensed under the MIT license.
    http://opensource.org/licenses/mit-license.php

    This program is intended to run on turtles working in a very specific
    environment, to collaboratively (optional) dig up blocks of interest in a
    designated area. Yes, it's a mining program ;)

    Features:
      - Fully resumable, thanks to LAMA and my state API. This resume is *very*
        stable. It even survived multiple game crashes (out of memory).
      - Interactively configurable (quarry size, torch placement).
      - Supports turtles cooperatively working on the same quarry, up to the
        total number of holes being dug - one turtle per hole, max. If there's
        fewer turtles than holes, the holes will be worked on sequentially.
      - Adding new turtles is super-easy, just place them into the dock, facing
        the fuel chest (away from the disk drive) and the environment will be
        installed on it and executed.

    To get started, set up the docking station like this (top-down view).

         CF       Where: CD = Chest for dropping found blocks.
      CD TU CT           CF = Chest with fuel.
         DD              CT = Chest with torches (only needed when used).
                         DD = A disk drive with an empty floppy inside.
                         TU = A turtle, looking at the fuel chest.

    Make sure the turtle in the middle is facing the fuel chest, then install
    the environment like this:
        > pastebin get h9KJ4DRt jam-install
        > jam-install

    The program will guide you through the next steps. Always make sure there's
    enough fuel (and if used, torches) in the chests, and empty the dropbox
    regularly!

    To add more turtles to an existing quarry, simply place them into the
    docking station like you did the first turtle, i.e. facing the fuel chest.
    It will automatically be configured by the program written onto the floppy
    disk when the quarry was set up and then run this program.
]]

assert(os.loadAPI("apis/bapil"))
assert(os.loadAPI("apis/logger"))
assert(os.loadAPI("apis/startup"))
assert(os.loadAPI("apis/state"))
assert(os.loadAPI("apis/lama"))

-------------------------------------------------------------------------------
-- Semi-config (you normally won't want to touch these)                      --
-------------------------------------------------------------------------------

-- The channel on which we'll send out status messages.
local sendChannel = 10113

-- Every how many levels torch placing turtles should place a torch.
local torchFrequency = 8

-- Whether to write our progress into a log file (each time the program changes
-- its state it would log that). This is primarily intended for debugging.
local writeLog = false

-- File in which to store current program state on the turtle, for resuming the
-- program after a reboot.
local stateFile = "/.jam-state"

-- The path to the file on the disk drive which we use to track how many jobs
-- we have already assigned to turtles. Note that this will be prefixed with
-- the disk drives mount path, so it should be a relative path.
local jobFile = ".jobs"

-- Given the turtle is in it's native orientation, this is the side the chest
-- we drop stuff we found into.
local dropSide = lama.side.left

-- Given the turtle is in it's native orientation, this is the side the chest
-- we can get fuel from.
local fuelSide = lama.side.front

-- Given the turtle is in it's native orientation, this is the side the chest
-- we can get new torches from.
local torchSide = lama.side.right

-- Given the turtle is in it's native orientation, this is the side the floppy
-- disk drive we use to track job progress on is at.
local diskSide = lama.side.back

-------------------------------------------------------------------------------
-- Internal variables / constants. DO NOT CHANGE THESE.                      --
-------------------------------------------------------------------------------

-- The slot number in which we keep our torches.
local torchSlot = 16

-- The relative level at which to move away from the dock, towards the holes.
local awayLevel = 1

-- The relative level at which to move back from the holes, towards the dock.
local backLevel = -1

-- Relative level at which to start digging.
local jobLevel = -2

-- Same as diskSide but using redstone.getSides() constants (for disk API).
local rsDiskSide = ({[lama.side.forward] = "front",
                     [lama.side.right]   = "right",
                     [lama.side.back]    = "back",
                     [lama.side.left]    = "left"})[diskSide]

-- The log we use. Print to screen if we're not supposed to log stuff.
local log = writeLog and logger.new("jam") or
            {info = function(_, fmt, ...)
                        print("[INFO] " .. string.format(fmt, ...))
                    end,
             warn = function(_, fmt, ...)
                        print("[WARNING] " .. string.format(fmt, ...))
                    end}

-- Forward declaration of namespaces.
local private

-------------------------------------------------------------------------------
-- Program states                                                            --
-------------------------------------------------------------------------------

-- Start assembling our state machine.
local program = state.new(stateFile)

--[[
    This state is purely used for interactively setting up a dig site. It asks
    the user a couple of questions, prepares the disk drive and then reboots
    into the actual worker loop.
]]
:add("setup", function()
    -- Make sure there's a disk drive behind us.
    if not disk.isPresent(rsDiskSide) or not disk.getMountPath(rsDiskSide) then
        lama.turn((diskSide + 2) % 4)
    end
    if not private.waitForDiskDrive(0.5) then
        return private.showBlueprint()
    end

    -- Configure the turtle to use our local coordinate system.
    lama.set(0, 0, 0, lama.side.north)

    -- If there's no job file on the disk drive we're starting from scratch.
    local diskPath = disk.getMountPath(rsDiskSide)
    local jobFileDisk = fs.combine(diskPath, jobFile)
    assert(not fs.exists(jobFileDisk) or not fs.isDir(jobFileDisk),
        "Bad disk, folder at job file location.")
    if not fs.exists(jobFileDisk) then
        assert(shell, "Setup must be run from the shell.")
        local jobCount, placeTorches,
              placeIgnored, haveIgnoreChest = private.setupDigSite()
        if jobCount == nil then
            -- nil is the abort signal, restart the state.
            return
        end

        -- Check for chests.
        print("Checking for chests...")
        lama.turn(dropSide)
        assert(turtle.detect(),
            "Bad setup detected, no drop chest found.")
        lama.turn(fuelSide)
        assert(turtle.detect(),
            "Bad setup detected, no fuel chest found.")
        if placeTorches or haveIgnoreChest then
            lama.turn(torchSide)
            assert(turtle.detect(),
                "Bad setup detected, no torch/ignored blocks chest found.")
        end

        -- Ask for ignored blocks in ignore chest before getting started.
        if haveIgnoreChest then
            private.showIgnoreChestInfo(placeIgnored)
        end

        -- If all went well, write the job file to the disk so that all turtles
        -- placed into the dock from now on will be initialized automatically.
        term.clear()
        term.setCursorPos(1, 1)
        print("Writing settings to disk... ")

        -- Fetch up-to-date path (may have changed after turning).
        lama.turn((diskSide + 2) % 4)
        private.waitForDiskDrive(0.5)
        local diskPath = disk.getMountPath(rsDiskSide)
        local jobFileDisk = fs.combine(diskPath, jobFile)
        local file = assert(fs.open(jobFileDisk, "w"),
                            "Could not open job file for writing.")
        file.write(textutils.serialize({totalJobs = jobCount,
                                        placeTorches = placeTorches,
                                        placeIgnored = placeIgnored,
                                        haveIgnoreChest = haveIgnoreChest}))
        file.close()
    end

    -- Next up: add this turtle as a worker to the quarry.
    switchTo("add_turtle")

    -- Finish initialization via disk startup. For example, this will install
    -- this program as an autorun script.
    os.reboot()
end)

--[[
    Given an existing dig site adds a new turtle to work on it.
]]
:add("add_turtle", function()
    -- Align back to face away from the disk drive.
    lama.turn((diskSide + 2) % 4)
    private.waitForDiskDrive(0.5)
    assert(disk.isPresent(rsDiskSide) and disk.getMountPath(rsDiskSide),
        "Bad setup detected, no disk in disk drive behind me!")

    -- Copy global quarry settings.
    local jobData = private.readJobData()
    placeIgnored = placeIgnored or jobData.placeIgnored
    placeTorches = placeTorches or jobData.placeTorches
    haveIgnoreChest = haveIgnoreChest or jobData.haveIgnoreChest

    -- Ask for the blocks to ignore to be placed in our inventory. Remember how
    -- many block types we're supposed to ignore.
    if haveIgnoreChest then
        ignoreCount = private.setupIgnoredBlocksFromIgnoreChest()
    else
        ignoreCount = private.setupIgnoredBlocks(placeTorches, placeIgnored)
        -- If we got nothing (nil) we're supposed to try again.
        if not ignoreCount then
            return
        end
    end

    -- Drop any duplicates we have of the stuff we're supposed to ignore.
    -- Switching to goto_drop is equivalent to drop, but more uniform flow.
    switchTo("goto_drop")
end)

--[[
    Go back to the docking station to drop stuff we picked up.
]]
:add("goto_drop", function()
    log:info("Going home to deliver the goods.")
    private.sendMessage("state", "goto_drop")

    private.select(1)
    local x, y, z = lama.get()
    local path = private.generatePath(x, y, z, 0, 0, 0, "home")
    private.forceMove("goto_drop", function()
        return lama.navigate(path, math.huge, true)
    end)

    switchTo("drop")
end)

--[[
    Actually drop anything in our inventory that's surplus.
]]
:add("drop", function()
    log:info("Dropping it!")
    private.sendMessage("state", "drop")

    if not placeIgnored or not job then
        for slot = 1, ignoreCount do
            if turtle.getItemCount(slot) > 1 then
                private.drop(slot, 1)
            end
        end
    end

    local function isIgnoredBlock(slot)
        if not ignoredLookup then
            return false
        end
        for i = 1, #ignoredLookup do
            if ignoredLookup[i] == slot then
                return true
            end
        end
        return false
    end
    for slot = ignoreCount + 1, 16 do
        if not placeTorches or slot ~= torchSlot then
            if not isIgnoredBlock(slot) then
                private.drop(slot)
            end
        end
    end

    -- Continue with our current job, or get a new one if we don't have one.
    if job then
        switchTo("refuel_job")
    else
        switchTo("get_job")
        -- Turn back to original orientation.
        lama.turn((diskSide + 2) % 4)
        -- We reboot before each job because this way the Lua VM gets a proper
        -- cleaning (not sure if that's what caused it, but running multiple
        -- turtles for extended periods made my worlds crash), and because I
        -- had a weird bug where the turtle would otherwise not see the disk
        -- inside the disk drive until either rebooted forcefully, or I opened
        -- the menu, shortly. Yes. I know. Totally insane, but 99% reproducible
        -- in that one world.
        os.reboot()
    end
end)

--[[
    Tries to get a job, on success refuels and executes it, otherwise refuels
    to move to retirement position (out of the way of other turtles).
]]
:add("get_job", function()
    log:info("Looking for a new job.")
    private.sendMessage("state", "get_job")

    -- Make sure the disk drive is behind us.
    assert(private.waitForDiskDrive(5),
        "Bad setup detected, no disk in disk drive behind me!")

    -- Returns a timestamp based on the ingame time (in ticks).
    local function timestamp()
        return (os.day() * 24 + os.time()) * 1000
    end

    -- Get the current job information.
    local jobData = private.readJobData()

    -- If we finished a job, clear it from the list of active jobs.
    if finishedJob and jobData.activeJobs and
       jobData.activeJobs[finishedJob]
    then
        -- Remember how long the last couple of jobs took to finish. This is
        -- useful for predicting when an active job has taken an unexpectedly
        -- long time and may require the player's investigation (via some
        -- stationary computer attached to the disk drive for example).
        local started = jobData.activeJobs[finishedJob]
        local finished = timestamp()
        local duration = finished - started
        jobData.jobDurations = jobData.jobDurations or {}
        table.insert(jobData.jobDurations, 1, duration)
        if #jobData.jobDurations > 10 then
            table.remove(jobData.jobDurations)
        end
        jobData.activeJobs[finishedJob] = nil
        finishedJob = nil
    end

    -- Try to get a new job.
    local nextJob = jobData.nextJob or 1
    if nextJob <= jobData.totalJobs then
        job = nextJob
        jobData.activeJobs = jobData.activeJobs or {}
        jobData.activeJobs[job] = timestamp()
        jobData.nextJob = job + 1
        if job == 1 then
            jobData.startTime = timestamp()
        end
        switchTo("refuel_job")
        log:info("Got one! Our new job ticket is #%d.", job)
        private.sendMessage("job", job)
    else
        endSlot = jobData.finished or 0
        jobData.finished = endSlot + 1
        jobData.stopTime = timestamp()
        switchTo("refuel_end")
    end

    -- Write new state back to disk.
    local diskPath = disk.getMountPath(rsDiskSide)
    local jobFileDisk = fs.combine(diskPath, jobFile)
    local file = assert(fs.open(jobFileDisk, "w"),
                  "Bad disk, failed to open job file for writing.")
    file.write(textutils.serialize(jobData))
    file.close()
end)

--[[
    Gets enough fuel to get to and back from our job.
]]
:add("refuel_job", function()
    log:info("Getting enough fuel to make it to our job and back.")
    private.sendMessage("state", "refuel_job")
    private.refuel(private.computeExpeditionCost(job), ignoreCount)
    switchTo("restock_torches")
end)

--[[
    Refills our torch stack.
]]
:add("restock_torches", function()
    if placeTorches then
        log:info("Picking up some torches to bring light into the dark.")
        private.sendMessage("state", "restock_torches")
        private.restockTorches(ignoreCount)
    end
    switchTo("goto_job")
end)

--[[
    Moves the turtle to the top of the hole it should dig.
]]
:add("goto_job", function()
    local tx, tz = private.computeCoordinates(job)
    log:info("On my way to my workplace @ (%d, %d)!", tx, tz)
    private.sendMessage("state", "goto_job")

    private.select(1)
    local x, y, z = lama.get()
    local path = private.generatePath(x, y, z, tx, jobLevel, tz, "job")
    private.forceMove("goto_job", function()
        return lama.navigate(path, math.huge, true, true) 
    end)

    if resumeDigUp then
        switchTo("dig_up")
    else
        switchTo("dig_down")
    end
end)

--[[
    Digs a hole down until we hit bedrock, returns to drop stuff if full and
    returns to where we left off.
]]
:add("dig_down", function()
    log:info("Looking for bedrock, can offer dancing skills.")
    private.sendMessage("state", "dig_down")

    if resumeDigDown then
        log:info("Resuming from where I took a break.")
        private.select(1)
        while lama.getY() > resumeDigDown do
            lama.down(math.huge, true)
        end
        resumeDigDown = nil
    end

    repeat
        local newSamples = private.digLevel(ignoreCount, ignoreSamples, true)
        if newSamples then
            ignoreSamples = newSamples
            save()
        end

        if private.isInventoryFull() then
            -- We may sample the blocks on the level we're on twice (again when
            -- coming back), but that's an acceptable simplification.
            resumeDigDown = lama.getY()
            return switchTo("goto_drop")
        end

        private.select(1)
        local brokeStuff, pickedSomethingUp =
            private.suckAndDig(turtle.suckDown, turtle.digDown)
        if (placeIgnored or placeTorches) and
           pickedSomethingUp and not groundLevel
        then
            groundLevel = lama.getY()
            save()
        end

        -- Only try to move down if we don't break anything while doing so. If
        -- suckAndDig() may return false even though there is something if our
        -- inventory is full and we should go empty it, so check if there's no
        -- block before we move.
        local couldMove = false
        if brokeStuff or not turtle.detectDown() then
            couldMove = lama.down(math.huge, true)
        end
    until not brokeStuff and not couldMove

    switchTo("rebuild_ignore_lookup")
end)

--[[
    Sorts the blocks we're supposed to ignore, if any, so that the most
    frequently encountered ones are at the lower inventory positions (for
    faster early exists when comparing).
]]
:add("rebuild_ignore_lookup", function()
    if placeIgnored and groundLevel then
        log:info("Checking for overflow of ignorance.")
        private.sendMessage("state", "rebuild_ignore_lookup")

        -- Swaps two slots in the inventory.
        local function swap(slotA, slotB)
            if slotA == slotB then
                return
            end

            -- Find an empty slot to work with as a temporary buffer.
            local slotTmp
            for slot = ignoreCount + 1, 16 do
                if turtle.getItemCount(slot) == 0 then
                    slotTmp = slot
                    break
                end
            end
            if not slotTmp then
                return false
            end

            private.select(slotA)
            turtle.transferTo(slotTmp)

            private.select(slotB)
            turtle.transferTo(slotA)

            private.select(slotTmp)
            turtle.transferTo(slotB)

            return true
        end

        -- Build a look-up table of slots that also contain ignored items in
        -- case we dug up so many we had an overflow. This is used for to avoid
        -- having to check the complete inventory when placing ignored blocks
        -- while moving up (which would be horribly slow).
        local count, nextSlot = 0, 16
        local lookup = {}
        for slot = 16, ignoreCount + 1, -1 do
            if turtle.getItemCount(slot) > 0 and
               not placeTorches or slot ~= torchSlot
            then
                -- Got a candidate, compare it to all known ignored blocks.
                private.select(slot)
                for ignoreSlot = 1, ignoreCount do
                    if turtle.compareTo(ignoreSlot) then
                        -- This is an ignored block. Try to push it to the back
                        -- of the inventory, to avoid ripping holes into the
                        -- inventory list when we deplete the stack, which can
                        -- lead to getting two stacks of the same item type of
                        -- dug up blocks (e.g.: coal at 5, additional cobble at
                        -- 4, cobble depletes, new coal found, goes to 4 ->
                        -- both 4 and 5 contain coal, where if cobble were
                        -- behind the coal they'd be merged (assuming what coal
                        -- we had wasn't a full stack already, of course).
                        count = count + turtle.getItemCount(slot)
                        if swap(slot, nextSlot) then
                            table.insert(lookup, 1, nextSlot)
                            nextSlot = nextSlot - 1
                        else
                            table.insert(lookup, 1, slot)
                        end
                        break
                    end
                end
            end
        end
        if #lookup > 0 then
            ignoredLookup = lookup
        end
        -- Add the counts for the excess items in the stacks of the reference
        -- slots (we only need to keep one of these).
        for slot = 1, ignoreCount do
            count = count + (turtle.getItemCount(slot) - 1)
        end
        -- Remember the level at which we can start placing ignored blocks so
        -- that we have enough up to the surface.
        placeIgnoredLevel = groundLevel - count
    end

    switchTo("dig_up")
end)

--[[
    Digs back up, picking up whatever isn't ignored. Returns home to drop
    stuff if inventory is full to resume where it we off.
]]
:add("dig_up", function()
    log:info("Moving up in the world.")
    private.sendMessage("state", "dig_up")

    -- Get back to where we stopped if we're resuming our job.
    if resumeDigUp then
        log:info("Resuming from where I took a break.")
        private.select(1)
        while lama.getY() > resumeDigUp do
            lama.down(math.huge, true)
        end
        resumeDigUp = nil
    end

    -- Break after block placement to guarantee we always place as necessary.
    while true do
        -- Try placing before moving, so that we can be sure we placed our
        -- thing if we restarted after finishing a move, but before placing.
        if groundLevel and lama.getY() <= groundLevel then
            -- Note that placeIgnored and placeTorches are mutually exclusive.
            if placeIgnored and not placeIgnoredLevel or
               lama.getY() > placeIgnoredLevel
            then
                -- Once we're above the level we can start placing our ignored
                -- blocks from we unset the variable to reduce state file size.
                if placeIgnoredLevel then
                    placeIgnoredLevel = nil
                    save()
                end

                -- Figure out which slot to place from, starting with overflow
                -- slots (stored in ignoreLookup, determined in sort state).
                local slot
                if ignoredLookup then
                    slot = ignoredLookup[#ignoredLookup]
                else
                    -- No more lookup-blocks. Draw from our reference stacks.
                    for i = 1, ignoreCount do
                        if turtle.getItemCount(i) > 1 then
                            slot = i
                            break
                        end
                    end
                end
                -- If no-one stole items from our inventory and we didn't
                -- miscalculate we should always have a slot by now.
                if slot then
                    private.select(slot)
                    turtle.placeDown()

                    if ignoredLookup then
                        if turtle.getItemCount(slot) == 0 then
                            table.remove(ignoredLookup)
                        end
                        if #ignoredLookup == 0 then
                            ignoredLookup = nil
                        end
                        save()
                    end
                else
                    groundLevel = nil
                end
            elseif placeTorches and lama.getY() % torchFrequency == 0 then
                private.select(torchSlot)
                turtle.placeDown()
            end
        else
            -- Reset after coming above ground level, to make the check fail
            -- at the first part and to reduce state file size.
            groundLevel = nil
        end

        -- Dig out the level.
        local newSamples = private.digLevel(ignoreCount, ignoreSamples, false)
        if newSamples then
            ignoreSamples = newSamples
            save()
        end

        -- Move up until we're back at our starting location.
        if lama.getY() >= jobLevel then
            break
        end

        if private.isInventoryFull() then
            -- We may sample the blocks on the level we're on twice (again when
            -- coming back), but that's an acceptable simplification.
            resumeDigUp = lama.getY()
            return switchTo("goto_drop")
        end

        private.select(1)
        private.forceMove("dig_up", function()
            return lama.up(math.huge, true)
        end)
    end

    finishedJob = job
    groundLevel = nil
    placeIgnoredLevel = nil
    ignoredLookup = nil
    job = nil
    switchTo("goto_drop")
end)

--[[
    Gets enough fuel to move to the graveyard.
]]
:add("refuel_end", function()
    log:info("Getting my last rites. Fuel! I meant fuel.")
    private.sendMessage("state", "refuel_end")

    -- Generate the path to our final resting place: two up, n forward and one
    -- to the side (so future finishing turtles can pass us by).
    local x, y, z = lama.get()
    local path = {
        {x = x, y = y, z = z},
        {x = 0, y = 2, z = 0},
        {x = 0, y = 2, z = endSlot},
        {x = 1, y = 2, z = endSlot}
    }
    private.refuel(private.computeFuelNeeded(path), ignoreCount)
    switchTo("clear_inventory")
end)

--[[
    Clear our inventory when we're done.
]]
:add("clear_inventory", function()
    log:info("Clearing out my inventory since I'm done with the world.")
    private.sendMessage("state", "clear_inventory")

    for slot = 1, 16 do
        private.drop(slot)
    end
    private.select(1)
    switchTo("goto_end")
end)

--[[
    Moves to *in front of* the slot where we'll shut down.
]]
:add("goto_end", function()
    log:info("Moving out of the way, I'm just useless junk anyway.")
    private.sendMessage("state", "goto_end")

    local x, y, z = lama.get()
    local path = private.generatePath(x, y, z, 0, 2, endSlot, "end")
    private.forceMove("goto_end", function()
        return lama.navigate(path, math.huge, true)
    end)

    switchTo("end")
end)

--[[
    Moves into the actual slot where we'll shut down and then die quietly.
]]
:add("end", function()
    log:info("That's it, I'm going to end it right here. It was a nice life.")
    private.sendMessage("state", "end")

    private.forceMove("end", function()
        return lama.moveto(1, 2, endSlot, lama.side.north, math.huge, true)
    end)

    startup.disable("jam")

    switchTo(nil)
end)

-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-- Utility functions                                                         --
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------

-- Private namespace.
private = {}

-------------------------------------------------------------------------------
-- Quarry and turtle setup                                                   --
-------------------------------------------------------------------------------

--[[
    Show instructions on how to set up a JAM quarry.
]]
function private.showBlueprint()
    term.clear()
    term.setCursorPos(1, 1)
    write("To use JAM you need to build a small  \n" ..
          "docking station. Build it like this:  \n" ..
          "                                      \n" ..
          "    CF     Where                      \n" ..
          " CD TU CT  CD: Chest for dropping     \n" ..
          "    DD         found blocks/items.    \n" ..
          "           CF: Chest with turtle fuel.\n" ..
          " CT: Chest with torches or blocks to  \n" ..
          "     ignore (depends on config).      \n" ..
          " DD: Disk drive with an empty disk.   \n" ..
          " TU: This turtle, back to the drive.  \n" ..
          "                                      \n" ..
          "When done, press [Enter] to continue.")
    private.prompt({keys.enter}, {})
end

--[[
    Show information about how to configure ignored blocks.
]]
function private.showIgnoreChestInfo(placeIgnored)
    term.clear()
    term.setCursorPos(1, 1)
    print("Please put the block types that you   \n" ..
          "want to avoid into the torch chest or \n" ..
          "my inventory. Insert as many each, as \n" ..
          "you wish to employ turtles (normally  \n" ..
          "one stack each should be plenty).   \n\n" ..
          "When done, press [Enter] to confirm.\n\n" ..
          "Recommended: Stone, Dirt and possibly \n" ..
          "Gravel or Sand (depends on the biome).\n" ..
          (placeIgnored and
          "You may also want to add Cobblestone, \n" ..
          "to allow placing it while moving up."
          or "" ))
    private.prompt({keys.enter}, {})
end

--[[
    Asks the user for the size of the dig site and configures the floppy disk.

    This function never returns, it reboots the turtle after it has run.
]]
function private.setupDigSite()
    -- Label the disk if it hasn't been labeled yet.
    if not disk.getLabel(rsDiskSide) or disk.getLabel(rsDiskSide) == "" then
        disk.setLabel(rsDiskSide, "JAM Job State")
    end
    local diskPath = disk.getMountPath(rsDiskSide)

    -- Ask the user how big of a dig site he'd like to create.
    term.clear()
    term.setCursorPos(1, 1)
    print("  Welcome to JAM: Just another Miner!\n\n" ..
          "Please tell me how large an area you  \n" ..
          "want to mine. The area will always be \n" ..
          "squared. Use the arrow keys to adjust \n" ..
          "the size, then press [Enter].         \n")
    local _, y = term.getCursorPos()
    local format = {"  Size: %d (%d chunk, %d hole)\n",
                    "  Size: %d (%d chunks, %d holes)\n"}
    print("\n")
    write("[left/right: one, up/down: five steps]\n\n" ..
          "(Note: chunks refers to the number of \n" ..
          "affected ones, not the worked on area)")
    local size, radius, chunks, jobCount = 1
    repeat
        local rx, ry = term.getCursorPos()
        radius = size * 3
        chunks = math.ceil(radius / 16)
        chunks = chunks * chunks
        jobCount = private.computeJobCount(radius)
        term.setCursorPos(1, y)
        term.clearLine()
        write(string.format(size == 1 and format[1] or format[2],
                            radius, chunks, jobCount))
        -- For termination not f*cking up the shell.
        term.setCursorPos(rx, ry)

        local _, code = os.pullEvent("key")
        if code == keys.right then
            -- Let's bound the maximum dig site size to the area of loaded
            -- chunks around a single player...
            size = math.min(55, size + 2)
        elseif code == keys.left then
            size = math.max(1, size - 2)
        elseif code == keys.up then
            size = math.min(55, size + 10)
        elseif code == keys.down then
            size = math.max(1, size - 10)
        end
    until code == keys.enter

    local upOption = 0
    repeat
        term.clear()
        term.setCursorPos(1, 1)
        print("While making their way up out of the\n" ..
              "holes they dug, do you want your    \n" ..
              "turtles to:                         \n")
        if upOption == 0 then
            print(" > Fill the hole with ignored blocks!\n\n" ..
                  "   Place torches every now and then?\n\n" ..
                  "   Just dig as fast as they can?      \n")
        elseif upOption == 1 then
            print("   Fill the hole with ignored blocks?\n\n" ..
                  " > Place torches every now and then!\n\n" ..
                  "   Just dig as fast as they can?      \n")
        elseif upOption == 2 then
            print("   Fill the hole with ignored blocks?\n\n" ..
                  "   Place torches every now and then?\n\n" ..
                  " > Just dig as fast as they can!      \n")
        end
        print("Please select one with the arrow keys \n" ..
              "and press [Enter] to confirm.")
        local _, code = os.pullEvent("key")
        if code == keys.up then
            upOption = (upOption - 1) % 3
        elseif code == keys.down then
            upOption = (upOption + 1) % 3
        end
    until code == keys.enter
    local placeIgnored = upOption == 0
    local placeTorches = upOption == 1

    local haveIgnoreChest = false
    if not placeTorches then
        term.clear()
        term.setCursorPos(1, 1)
        print("Since the turtles won't need one of \n" ..
              "the chests for torches, you can     \n" ..
              "instead place blocks you want your  \n" ..
              "turtles to ignore in that chest.    \n" ..
              "This way you won't have to add them \n" ..
              "to each one individually. You'll    \n" ..
              "have to place exacly one stack of at\n" ..
              "least a size equal to the number of \n" ..
              "turtles you plan to use into the    \n" ..
              "torch chest.\n")
        write("Do you want to do this? [Y/n] > ")
        haveIgnoreChest = private.prompt()
    end

    term.clear()
    term.setCursorPos(1, 1)
    print("Please confirm your settings\n\n" ..
          "  Radius: " .. radius .. "\n" ..
          "    Affected chunks: " .. chunks .. "\n" ..
          "    Holes/Jobs: " .. jobCount     .. "\n" ..
          "  Place blocks: " .. tostring(placeIgnored) .. "\n" ..
          "  Place torches: " .. tostring(placeTorches) .. "\n" ..
          "  Blocks to ignore in chest: " .. tostring(haveIgnoreChest))
    write("\nIs this correct? [Y/n] > ")
    if not private.prompt() then
        -- nil causes restart.
        return nil
    end

    -- Set up the disk so that it installs the script to any
    -- turtle that starts up while in front of it.
    term.clear()
    term.setCursorPos(1, 1)
    print("Writing initialization data to disk...")

    local install = {
        {from = bapil.resolveAPI("apis/bapil"),
         to   = fs.combine(diskPath, "apis/bapil")},
        {from = bapil.resolveAPI("apis/lama"),
         to   = fs.combine(diskPath, "apis/lama")},
        {from = bapil.resolveAPI("apis/logger"),
         to   = fs.combine(diskPath, "apis/logger")},
        {from = bapil.resolveAPI("apis/stacktrace"),
         to   = fs.combine(diskPath, "apis/stacktrace")},
        {from = bapil.resolveAPI("apis/startup"),
         to   = fs.combine(diskPath, "apis/startup")},
        {from = bapil.resolveAPI("apis/state"),
         to   = fs.combine(diskPath, "apis/state")},
        {from = shell.getRunningProgram(),
         to   = fs.combine(diskPath, "programs/jam")},
        {from = "programs/jam-status",
         to   = fs.combine(diskPath, "programs/jam-status")},
        -- We write a startup file to the disk drive that will install our
        -- environment to any new turtles started up in front of it. This is
        -- pretty much the same we do here, in reverse.
        {content = string.format(
[=[-- Ignore anything that isn't a turtle.
if not turtle then
    return fs.exists("/startup") and dofile("/startup")
end

-- Ignore if we're on the wrong side. Otherwise get the mount path of the disk.
local diskSide = %q
local diskPath = disk.getMountPath(diskSide)
if not disk.isPresent(diskSide) then
    return fs.exists("/startup") and dofile("/startup")
end

-- Update the environment, copy APIs, create startup file, that kind of stuff.
print("Updating JAM installation...")

-- Set label if necessary.
if os.getComputerLabel() == nil or os.getComputerLabel() == "" then
    os.setComputerLabel("JAM-" .. os.getComputerID())
end

-- List of files we put on our turtles.
local install = {
    {from = fs.combine(diskPath, "apis/bapil"),
     to   = "/apis/bapil"},
    {from = fs.combine(diskPath, "apis/lama"),
     to   = "/apis/lama"},
    {from = fs.combine(diskPath, "apis/logger"),
     to   = "/apis/logger"},
    {from = fs.combine(diskPath, "apis/stacktrace"),
     to   = "/apis/stacktrace"},
    {from = fs.combine(diskPath, "apis/startup"),
     to   = "/apis/startup"},
    {from = fs.combine(diskPath, "apis/state"),
     to   = "/apis/state"},
    {from = fs.combine(diskPath, "programs/jam"),
     to   = "/programs/jam"},
    {content =
[[if startup then return false end
os.loadAPI("apis/bapil")
bapil.hijackOSAPI()
shell.setPath(shell.path() .. ":/programs")
assert(os.loadAPI("apis/stacktrace"))
_G.pcall = stacktrace.tpcall
assert(os.loadAPI("apis/startup"))
-- Avoid tail-recursion optimization removing our environment from the stack.
return startup.run() or false]],
     to = "/startup", keep = true}
}

local function areDifferent(f1, f2)
    local s1 = fs.getSize(f1)
    local s2 = fs.getSize(f2)
    if s1 == 512 or s2 == 512 then return true end
    s1 = s1 - fs.getName(f1):len()
    s2 = s2 - fs.getName(f2):len()
    return s1 ~= s2
end

local requiredDiskSpace, folders = 0, {}
for _, entry in ipairs(install) do
    assert(not fs.exists(entry.to) or not fs.isDir(entry.to),
        "Bad turtle, folder in location " .. entry.to)
    local folder = entry.to:sub(1, #entry.to - fs.getName(entry.to):len())
    assert(not fs.exists(folder) or fs.isDir(folder),
           "Bad turtle, file in location " .. folder)
    if not fs.exists(folder) and not folders[folder] then
        requiredDiskSpace = requiredDiskSpace + 512
        folders[folder] = true
    end

    if not fs.exists(entry.to) or not entry.keep then
        if entry.from then
            assert(fs.exists(entry.from) and not fs.isDir(entry.from),
                "Bad disk, missing file " .. entry.from)
            if not fs.exists(entry.to) or
               areDifferent(entry.from, entry.to)
            then
                fs.delete(entry.to)
                requiredDiskSpace = requiredDiskSpace + fs.getSize(entry.from)
            end
        elseif entry.content then
            if not fs.exists(entry.to) or
               areDifferent(#entry.content, entry.to)
            then
                fs.delete(entry.to)
                requiredDiskSpace = requiredDiskSpace + #entry.content
            end
        end
    end
end

if requiredDiskSpace > fs.getFreeSpace(diskPath) then
    print("Not enough space on turtle. Please make some and try again.")
    return false
end

for folder, _ in pairs(folders) do fs.makeDir(folder) end
for _, entry in ipairs(install) do
    print(" > " .. entry.to)
    if entry.from then
        if not fs.exists(entry.to) then
            fs.copy(entry.from, entry.to)
        end
    elseif entry.content then
        if not fs.exists(entry.to) then
            local file = fs.open(entry.to, "w")
            file.write(entry.content)
            file.close()
        end
    end
    os.sleep(0.1)
end

-- Run local startup script.
if not dofile("/startup") then return false end

-- The local startup file should have loaded our APIs.
assert(startup, "Bad installation, startup API not loaded automatically.")

-- Overwrite this program in case of updates (different file size).
if not startup.isEnabled("jam") then
    startup.remove("jam")
    startup.addFile("jam", 20, "programs/jam")
    print("Done installing JAM, rebooting...")
    os.sleep(1)
    os.reboot()
end]=], rsDiskSide),
         to = fs.combine(diskPath, "startup")}
    }

    -- Compute total disk space required and which folders we need to create.
    local requiredDiskSpace, folders = 0, {}
    for _, entry in ipairs(install) do
        assert(not fs.exists(entry.to) or not fs.isDir(entry.to),
            "Bad disk, folder in location " .. entry.to)
        local folder = entry.to:sub(1, #entry.to - fs.getName(entry.to):len())
        assert(not fs.exists(folder) or fs.isDir(folder),
               "Bad disk, file in location " .. folder)
        if not fs.exists(folder) and not folders[folder] then
            requiredDiskSpace = requiredDiskSpace + 512
            folders[folder] = true
        end

        if entry.from then
            assert(fs.exists(entry.from) and not fs.isDir(entry.from),
                "Bad setup, missing file " .. entry.from)
            if not fs.exists(entry.to) or
               private.areDifferent(entry.from, entry.to)
            then
                fs.delete(entry.to)
                requiredDiskSpace = requiredDiskSpace + fs.getSize(entry.from)
            end
        elseif entry.content then
            if not fs.exists(entry.to) or
               private.areDifferent(#entry.content, entry.to)
            then
                fs.delete(entry.to)
                requiredDiskSpace = requiredDiskSpace + #entry.content
            end
        end
    end

    print("Additional disk space required: " ..
          math.ceil(requiredDiskSpace / 1024) .. "KB.")
    if requiredDiskSpace > fs.getFreeSpace(diskPath) then
        print("\nNot enough space on attached disk.\n")
        if not private.formatDisk() then
            -- nil causes restart.
            return nil
        end
    end

    for folder, _ in pairs(folders) do
        fs.makeDir(folder)
    end
    for _, entry in ipairs(install) do
        print(" > " .. entry.to)
        if entry.from then
            if not fs.exists(entry.to) then
                fs.copy(entry.from, entry.to)
            end
        elseif entry.content then
            if not fs.exists(entry.to) then
                local file = fs.open(entry.to, "w")
                file.write(entry.content)
                file.close()
            end
        end
        os.sleep(0.1)
    end

    return jobCount, placeTorches, placeIgnored, haveIgnoreChest
end

--[[
    This function asks the user to put blocks that should be ignored into the
    turtle's inventory and does some sanity checks on the found blocks.

    @return the number of block types to ignore.
]]
function private.setupIgnoredBlocks(placeTorches, placeIgnored)
    -- If we come here a dig site has already been set up, so we just need to
    -- know which block types to ignore.
    term.clear()
    term.setCursorPos(1, 1)
    print("Please put one of each block type that\n" ..
          "you want to avoid into my inventory.  \n" ..
          "When done, press [Enter] to confirm.\n\n" ..
          "Oh, and you can place the blocks into \n" ..
          "any slot you want, I'll put them into \n" ..
          "the right ones myself \\o/          \n\n" ..
          "Recommended: Stone, Dirt and possibly \n" ..
          "Gravel or Sand (depends on the biome).\n" ..
          (placeIgnored and
          "You may also want to add Cobblestone, \n" ..
          "to allow placing it while moving up."
          or "" ))
    private.prompt({keys.enter}, {})
    print("OK, let me see...")

    -- Move stuff from anywhere in the inventory into the first slots, so that
    -- we have a continuous interval of occupied slots.
    local slot, free = 1
    while slot <= 16 do
        if turtle.getItemCount(slot) > 0 then
            private.select(slot)
            for i = 1, slot - 1 do
                if turtle.compareTo(i) then
                    if not turtle.transferTo(i) or
                       turtle.getItemCount(slot) > 0
                    then
                        term.clear()
                        term.setCursorPos(1, 1)
                        print("Well, I tried to reduce the redundant  \n" ..
                              "stuff you gave me into one pile, but I \n" ..
                              "failed horribly. Cut me some slack. ;) \n" ..
                              "Please try only giving one block per   \n" ..
                              "block type, m'kay?                     \n")
                        print("Press [Enter] to try again m(.,.)m")
                        private.prompt({keys.enter}, {})
                        -- Restarts the state.
                        return nil
                    end
                    break
                end
            end
            if free and turtle.getItemCount(slot) > 0 then
                private.select(slot)
                turtle.transferTo(free)
                slot = free
                free = nil
            end
        end
        -- Might have become free while merging blocks.
        if turtle.getItemCount(slot) == 0 and free == nil then
            free = slot
        end
        slot = slot + 1
    end

    -- See how many blocks we have.
    local occupied = 0
    for slot = 1, 16 do
        if turtle.getItemCount(slot) > 0 then
            occupied = occupied + 1
        end
    end

    term.clear()
    term.setCursorPos(1, 1)
    if occupied == 0 then
        print("Woah, you want me to fetch, like,     \n" ..
              "everything? Even stone? That'll mean a\n" ..
              "lot of additional running back and    \n" ..
              "and forth, which is less efficient /o\\\n\n")
        write("Are you sure? [y/N] > ")
        if not private.prompt({keys.y}, {keys.n, keys.enter}) then
            -- Restarts the state.
            return nil
        end
        print("Oh boy... well, here goes nothing!")
    elseif occupied == 16 then
        print("You can't be serious, right? There's \n" ..
              "just no way this could possibly work.\n" ..
              "I need at least one free slot into   \n" ..
              "which I can put the stuff I dig up.  \n")
        print("Press [Enter] to try again -.-")
        private.prompt({keys.enter}, {})
        -- Restarts the state.
        return nil
    elseif occupied == 15 and placeTorches then
        print("Nice try, but this can't work in my  \n" ..
              "current configuration, since I need  \n" ..
              "one additional slot for the torches  \n" ..
              "I'm supposed to place. So I need some\n" ..
              "more room to store the stuff I dig up\n" ..
              "in. Meaning at least two free slots  \n" ..
              "in total. Can you do that for me?    \n")
        print("Press [Enter] to try again :/")
        private.prompt({keys.enter}, {})
        -- Restarts the state.
        return nil
    elseif placeTorches and occupied >= torchSlot then
        print("Unless you messed with the code this \n" ..
              "should not happen: the inventory     \n" ..
              "range used for blocks to ignore      \n" ..
              "intersects with the torch. You'll    \n" ..
              "have to specify less than " ..
              (torchSlot - 1) .. " block   \n" ..
              "types. Press [Enter] to try again... \n")
        private.prompt({keys.enter}, {})
        -- Restarts the state.
        return nil
    elseif occupied > 6 then
        print("While this is technically a feasible \n" ..
              "configuration, I'd highly recommend  \n" ..
              "adding fewer blocks to ignore. The   \n" ..
              "more blocks I have to check the more \n" ..
              "often I have to go back to clear my  \n" ..
              "inventory, and the longer it takes   \n" ..
              "to check if I may dig up a block ^.- \n\n" ..
              "Is this really what you want?          ")
        write("[Y/n] > ")
        if not private.prompt() then
            -- Restarts the state.
            return nil
        end
        print("Well, if you say so... ley's do this!")
    else
        local agree = {
            "Sounds reasonable.",
            "Yeah, that seems about right.",
            "As you command, my master!",
            "I humbly obey.",
            "Wow, you've got taste.",
            "Off I go then!",
            "Here I go!",
            "Work, work."
        }
        print(agree[math.random(1, #agree)])
    end
    os.sleep(1.5)
    return occupied
end

--[[
    An automated version for getting the blocks we should ignore.
]]
function private.setupIgnoredBlocksFromIgnoreChest()
    lama.turn(torchSide)
    private.select(1)

    assert(turtle.detect(), "Chest with ignored blocks disappeared!")

    -- If we're resuming in here, it means we only have stuff we're supposed
    -- to ignore in our inventory. Dump it back and start over.
    for slot = 1, 16 do
        if turtle.getItemCount(slot) > 0 then
            private.select(slot)
            assert(turtle.drop(), "Chest with blocks to ignore is full!")
        end
    end

    -- Suck as often as we can. If there's more, silently ignore it.
    private.select(1)
    for slot = 1, 15 do
        if not turtle.suck() then
            -- Stop if there's nothing else in there.
            break
        end
    end
    -- Put everything except one item back.
    for slot = 1, 15 do
        if turtle.getItemCount(slot) > 0 then
            private.select(slot)
            turtle.drop(turtle.getItemCount(slot) - 1)
        else
            break
        end
    end

    -- Merge duplicates, compact the range and dump duplicates.
    for slot = 2, 16 do
        -- Ignore empty slots.
        if turtle.getItemCount(slot) > 0 then
            -- Compare to all preceding slots
            for otherSlot = 1, slot - 1 do
                if turtle.compareTo(otherSlot) then
                    -- Got one of the same kind, try to merge.
                    if not turtle.transferTo(otherSlot) or
                       turtle.getItemCount(slot) > 0
                    then
                        -- Could not merge (other stack already full) or still
                        -- have some left (other stack is now full and there's
                        -- still some left here). Drop the remainder.
                        assert(turtle.drop(),
                            "Chest with blocks to ignore is full!")
                    end
                end
            end
        end
        -- If there's still something in the slot we didn't find anything of
        -- the same kind in our inventory. Look for an empty slot at a lower
        -- index to get a continuous segment.
        if turtle.getItemCount(slot) > 0 then
            for otherSlot = 1, slot - 1 do
                if turtle.getItemCount(otherSlot) == 0 then
                    turtle.transferTo(otherSlot)
                    break
                end
            end
        end
    end

    -- Count the remaining number of ignored block types and return that.
    local count = 0
    for slot = 1, 16 do
        if turtle.getItemCount(slot) > 0 then
            count = count + 1
        else
            break
        end
    end
    return count
end

--[[
    Reads a single key input from the user and returns whether the prompt was
    confirmed or denied.

    @param yesKeys a single or multiple keys that indicate success.
    @param noKeys a single or multiple keys that indicate denial.
    @return whether the user accepted or denied the prompt.
]]
function private.prompt(yesKeys, noKeys)
    yesKeys = yesKeys or {keys.y, keys.enter}
    noKeys = noKeys or {keys.n}
    if not type(yesKeys) == "table" then
        yesKeys = {yesKeys}
    end
    if not type(noKeys) == "table" then
        noKeys = {noKeys}
    end
    local result
    term.setCursorBlink(true)
    repeat
        local _, code = os.pullEvent("key")
        for _, k in pairs(yesKeys) do
            if code == k then
                result = true
                break
            end
        end
        for _, k in pairs(noKeys) do
            if code == k then
                result = false
                break
            end
        end
    until result ~= nil
    term.setCursorBlink(false)
    return result
end

--[[
    Checks if two files are potentially different by comparing their file
    sizes.
]]
function private.areDifferent(file1, file2)
    local s1 = type(file1) == "string" and fs.getSize(file1) or file1
    local s2 = fs.getSize(file2)
    if s1 == 512 or s2 == 512 then
        return true
    end
    s1 = type(file1) == "string" and s1 - fs.getName(file1):len() or s1
    s2 = s2 - fs.getName(file2):len()
    return s1 ~= s2
end

--[[
    Formats the attached disk drive.
]]
function private.formatDisk()
    if not disk.isPresent(rsDiskSide) then
        return true
    end
    local diskPath = disk.getMountPath(rsDiskSide)
    if #fs.list(diskPath) < 1 then
        return true
    end
    print("This will format the disk in the      \n" ..
          "attached disk drive. All data will be \n" ..
          "irretrievably lost.                 \n\n" ..
          "Are you sure? [Y/n]")
    if not private.prompt() then
        print("Aborting.")
        -- Eat key event so it doesn't propagate into the shell.
        os.sleep(0.1)
        return false
    end
    print("Formatting disk...")
    for _, file in pairs(fs.list(diskPath)) do
        local path = fs.combine(diskPath, file)
        print(" > " .. file .. (fs.isDir(path) and "/*" or ""))
        fs.delete(path)
        os.sleep(0.1)
    end
    return true
end

--[[
    Resets the disk and program and removes our startup script.
]]
function private.reset()
    program:reset()
    startup.remove("jam")
    if not disk.isPresent(rsDiskSide) or not disk.getMountPath(rsDiskSide) then
        lama.turn((diskSide + 2) % 4)
    end
    private.waitForDiskDrive(0.5)
    return private.formatDisk()
end

-------------------------------------------------------------------------------
-- Job position related stuff                                                --
-------------------------------------------------------------------------------

--[[
    Utility function to determine how many holes we can dig so that our spiral
    doesn't exceed the specified bounds.

    @param squareSize the size of the bounding square our dig operation has
        to fit into.
    @return the number of holes we will dig.
    @private
]]
function private.computeJobCount(squareSize)
    if squareSize < 0 then
        return 0
    end
    -- Subtract one for the center, then divide by six, because each following
    -- layer adds an additional six blocks.
    local spiralRadius = math.floor((squareSize - 1) / 6)
    -- Since we still have a square and we now know the number of layers, the
    -- number of holes is simply the length of one side squared.
    local sideLength = spiralRadius * 2 + 1
    return sideLength * sideLength
end

--[[
    Computes the actual x and y coordinates of the nth hole.

    @param n the number of the hole to compute the coordinates for.
    @return (x, y) being heightless the coordinates of the nth hole.
    @private
]]
function private.computeCoordinates(n)
    -- Adjust to zero indexed system.
    n = n - 1
    -- If we're at the origin we can return right away. In fact, we should,
    -- since we'd get a division by zero in the following...
    if n < 1 then
        return 0, 0
    end
    -- Compute the coordinates on a plain old rectangular spiral, first.
    local shell = math.floor((math.sqrt(n) + 1) / 2)
    local tmp = (2 * shell - 1); tmp = tmp * tmp
    local leg = math.floor((n - tmp) / (2 * shell))
    local element = (n - tmp) - (2 * shell * leg) - shell + 1
    local x, y
    if leg == 0 then
        x, y = shell, element
    elseif leg == 1 then
        x, y = -element, shell
    elseif leg == 2 then
        x, y = -shell, -element
    else
        x, y = element, -shell
    end
    -- Then map it to our knights move grid.
    return x * 2 - y, y * 2 + x
end

--[[
    Computes how much fuel we should stock up on for making sure we can safely
    travel to the specified dig site, dig it up, and come back.
]]
function private.computeExpeditionCost(job)
    local x, z = private.computeCoordinates(job)
    -- Start at home, move to the job location (layer enforced by function).
    local path = private.generatePath(0, 0, 0, x, jobLevel, z, "job")
     -- Digging faaar down, worst case scenario.
    table.insert(path, {x = x, y = -255, z = z})
    -- Append our way back home (again, move layer enforced by generatePath()).
    local pathBack = private.generatePath(x, jobLevel, z, 0, 0, 0, "home")
    for _, point in ipairs(pathBack) do
        table.insert(path, point)
    end
    return private.computeFuelNeeded(path)
end

--[[
    Computes how much fuel is needed to travel along the specified path.

    @param path the path to compute the fuel requirement for.
    @return the required fuel to travel the path.
    @private
]]
function private.computeFuelNeeded(path)
    local function fuel(from, to)
        local dx = math.abs(to.x - from.x)
        local dy = math.abs(to.y - from.y)
        local dz = math.abs(to.z - from.z)
        return dx + dy + dz
    end
    local result = 0
    local previous = nil
    for _, current in ipairs(path) do
        if previous then
            result = result + fuel(previous, current)
        end
        previous = current
    end
    return result
end

--[[
    Computes a path leading from or to the docking station, from and to to the
    specified coordinates.

    When moving away from the docking station we move in the layer above it,
    when returning to it in the layer below it.
]]
function private.generatePath(sx, sy, sz, tx, ty, tz, target)
    if sx == tx and sz == tz then
        if sy == ty then
            return {}
        end
        return {{x = tx, y = ty, z = tz}}
    end
    local layer
    if target == "home" then
        layer = backLevel
    elseif target == "end" then
        layer = 2
    elseif target == "job" then
        layer = awayLevel
    else
        error("'target' is invalid")
    end
    return {
        -- Start at the base station.
        {x = sx, y = sy,    z = sz},
        -- Move one up to the layer we use for moving away.
        {x = sx, y = layer, z = sz},
        -- Move to above the actual coordinates but on the same layer.
        {x = tx, y = layer, z = tz},
        -- Move down to where we want to go.
        {x = tx, y = ty,    z = tz}
    }
end

-------------------------------------------------------------------------------
-- Working turtle stuff                                                      --
-------------------------------------------------------------------------------

--[[
    Sends a message via WIFI if available.

    @param the message category, i.e. the type of the message.
    @param the actual message content.
]]
function private.sendMessage(category, message)
    if private.noModem then
        return
    elseif not private.modem then
        if peripheral.isPresent("right") and
           peripheral.getType("right") == "modem"
        then
            private.modem = peripheral.wrap("right")
        elseif peripheral.isPresent("left") and
               peripheral.getType("left") == "modem"
        then
            private.modem = peripheral.wrap("left")
        else
            -- Don't try again.
            private.noModem = true
            return
        end
    end
    local packet = {}
    packet.source = os.getComputerID()
    packet.sourceLabel = os.getComputerLabel()
    packet.category = category
    packet.message = message
    private.modem.transmit(sendChannel, 0, textutils.serialize(packet))
end

function private.waitForDiskDrive(secondsToWait)
    -- Wait a bit to finish moving and connect to the disk drive. This is
    -- really weird, but apparently a disk drive can be 'present' before it is
    -- mounted. So we wait until it's actually mounted... damn timining
    -- problems. We limit our number of tries, in case the disk drive was
    -- removed or - by some *very* slim chance - we're not in the right spot.
    -- Try for a total of five seconds, so lag is a non-issue.
    for i = 1, secondsToWait * 10 do
        if disk.isPresent(rsDiskSide) and disk.getMountPath(rsDiskSide) then
            return true
        end
        os.sleep(0.1)
    end
    return false
end

function private.readJobData()
    local diskPath = disk.getMountPath(rsDiskSide)
    local jobFileDisk = fs.combine(diskPath, jobFile)

    local file = assert(fs.open(jobFileDisk, "r"),
                        "Bad disk, could not find job file.")
    local jobData = textutils.unserialize(file.readAll())
    file.close()

    assert(type(jobData) == "table", "Bad disk, invalid job data.")

    return jobData
end

--[[
    Checks if all inventory slots are occupied.
]]
function private.isInventoryFull()
    for slot = 1, 16 do
        if turtle.getItemCount(slot) == 0 then
            return false
        end
    end
    return true
end

--[[
    Gets the total number of items in the turtles inventory.
]]
function private.itemCount()
    local count = 0
    for slot = 1, 16 do
        count = count + turtle.getItemCount(slot)
    end
    return count
end

--[[
    Replacement for turtle.select() that tracks the currently selected slot so
    selecting the same slot again becomes a no-op.
]]
function private.select(slot)
    if slot ~= private.selectedSlot then
        turtle.select(slot)
        private.selectedSlot = slot
    end
end

--[[
    Tries to empty out any inventories and then dig up the block.
]]
function private.suckAndDig(suck, dig)
    suck = suck or turtle.suck
    dig = dig or turtle.dig
    while true do
        if private.isInventoryFull() then
            return nil
        end
        if not suck() then
            local count = private.itemCount()
            local result = dig()
            return result, count ~= private.itemCount()
        end
    end
end

--[[
    Sorts the lookup table for ignore slots so that we iterate them in the
    order of their frequencies.

    This takes some measures to avoid rebuilding the sort order
]]
function private.computeIgnoreOrder(ignoreCount, ignoreSamples)
    if not private.orderedIgnoreSlots then
        -- Re-use the table to go easy on the GC.
        private.orderedIgnoreSlots = {}
        for i = 1, ignoreCount do
            table.insert(private.orderedIgnoreSlots, i)
        end
    end
    -- This is done quite often, but since this table will be really small it
    -- doesn't matter.
    if ignoreSamples then
        local function comparator(slotA, slotB)
            return (ignoreSamples[slotA] or 0) > (ignoreSamples[slotB] or 0)
        end
        table.sort(private.orderedIgnoreSlots, comparator)
    end
    return private.orderedIgnoreSlots
end

--[[
    Used to repeat a move until it succeeds. This *should* be unnecessary. I'm
    pretty sure I fixed LAMA up so that this it cannot happen, unless there's
    really an unbreakable block in our way all of a sudden (player placed?).
    But you just never know, so let's just keep trying hard...
]]
function private.forceMove(where, move)
    repeat
        local success, reason = move()
        if not success then
            log:warn("%s: unexpectedly couldn't move (%s)", where, reason)
            -- This really shouldn't happen ever anyway, but if it does, don't
            -- spam too hard.
            os.sleep(30)
        end
    until success
end

--[[
    -- Digs out a level either on the way up or down.
]]
function private.digLevel(ignoreCount, ignoreSamples, goingDown)
    -- Dig out two sides each while going down and up. Minimize turns by
    -- alternating the order between even and odd levels.
    local sides = ({
        -- Downwards.
        [true]  = {
            -- Even layer.
            [true] = {lama.side.north, lama.side.east},
            -- Odd layer.
            [false] = {lama.side.east, lama.side.north}
        },
        -- Upwards.
        [false] = {
            -- Even layer.
            [true] = {lama.side.south, lama.side.west},
            -- Odd layer.
            [false] = {lama.side.west, lama.side.south}
        }
    })[goingDown][lama.getY() % 2 == 0]

    -- Get the order in which to check the ignored items.
    local order = private.computeIgnoreOrder(ignoreCount, ignoreSamples)

    local droppedChanged = false
    for _, side in ipairs(sides) do
        lama.turn(side)
        if turtle.detect() then
            -- There's something there! Check if we should ignore it.
            local ignored = false
            for i = 1, ignoreCount do
                local slot = order[i]
                private.select(slot)
                if turtle.compare() then
                    -- Yep, ignore this one. Update our sampling.
                    ignored = true
                    ignoreSamples = ignoreSamples or {}
                    ignoreSamples[slot] = (ignoreSamples[slot] or 0) + 1
                    droppedChanged = true
                    break
                end
            end
            if not ignored then
                private.select(ignoreCount + 1)
                if private.suckAndDig() == nil then
                    -- Only returns nil if the inventory is full. Early exit in
                    -- that case to potentially avoid an unnecessary turn.
                    break
                end
            end
        end
    end
    return droppedChanged and ignoreSamples or nil
end

--[[
    Drop the contents of the specified slot, keeping only a specific amount.
    This keeps trying to drop until it succeeds.
]]
function private.drop(slot, keep)
    keep = keep or 0
    -- Don't spam the log. We DO spam the WIFI, though, since that can fail.
    local didLogFull = false
    while turtle.getItemCount(slot) > keep do
        lama.turn(dropSide)
        assert(turtle.detect(), "The dropbox disappeared!")
        private.select(slot)
        if not turtle.drop(turtle.getItemCount(slot) - keep) then
            private.sendMessage("full", "The drop chest is full!")
            if not didLogFull then
                didLogFull = true
                log:warn("The drop chest is full! Waiting...")
            end
            os.sleep(5)
        end
    end
end

--[[
    Refuels the turtle to the specified fuel level. This keeps retrying until
    it succeeds.
]]
function private.refuel(needed, ignoreCount)
    -- Don't spam the log. We DO spam the WIFI, though, since that can fail.
    local didLogNoFuel = false
    local fuelSlot = ignoreCount + 1
    while turtle.getFuelLevel() < needed do
        private.select(fuelSlot)
        if turtle.getItemCount(fuelSlot) == 0 then
            lama.turn(fuelSide)
            assert(turtle.detect(), "The fuel chest disappeared!")
            if not turtle.suck() then
                private.sendMessage("fuel", "We're all out fuel!")
                if not didLogNoFuel then
                    didLogNoFuel = true
                    log:warn("The fuel chest is empty! Waiting...")
                end
                os.sleep(5)
            end
        else
            while turtle.getItemCount(fuelSlot) > 0 and
                  turtle.getFuelLevel() < needed
            do
                if not lama.refuel(1) then
                    private.drop(fuelSlot)
                    break
                end
            end
            turtle.drop()
        end
    end
    private.drop(fuelSlot)
end

--[[
    Restock on torches to get a full stack. This keeps retrying until it
    succeeds.
]]
function private.restockTorches(ignoreCount)
    -- Don't spam the log. We DO spam the WIFI, though, since that can fail.
    local didLogNoTorches = false
    local tempSlot = ignoreCount + 1
    while turtle.getItemCount(torchSlot) < (256 / torchFrequency) do
        -- Select an empty slot because we cannot control how much we pull,
        -- then replenish our actual torch stack from that and drop the rest.
        private.select(tempSlot)
        -- Make sure our temp slot is empty or has torches in it.
        if turtle.getItemCount(tempSlot) > 0 and
           -- If we don't have any torches left we cannot be sure that whatever
           -- we have in our temp slot are torches, so we drop them. Otherwise
           -- we assume whatever is in our torch slot are guaranteed to be
           -- torches.
           (turtle.getItemCount(torchSlot) == 0 or
            not turtle.compareTo(torchSlot))
        then
            private.drop(tempSlot)
        end
        lama.turn(torchSide)
        assert(turtle.detect(), "The torch chest disappeared!")
        -- At this point we can be sure that if there's something in our temp
        -- slot it's torches, so use them up first, before sucking up more.
        if turtle.getItemCount(tempSlot) > 0 or turtle.suck() then
            turtle.transferTo(torchSlot)
            -- Put back any surplus.
            turtle.drop()
        else
            private.sendMessage("torches", "We're all out of torches!")
            if not didLogNoTorches then
                didLogNoTorches = true
                log:warn("The torch chest is empty! Waiting...")
            end
            os.sleep(5)
        end
    end

    private.drop(tempSlot)
end

-------------------------------------------------------------------------------
-- Environment checking                                                      --
-------------------------------------------------------------------------------

assert(turtle, "JAM only works on turtles.")

assert(type(stateFile) == "string" and stateFile ~= "",
    "The setting 'stateFile' must be a non-empty string.")

assert(type(jobFile) == "string" and jobFile ~= "",
    "The setting 'jobFile' must be a non-empty string.")

assert(rawget(lama.side, dropSide),
    "The setting 'dropSide' must be a valid lama.side.")

assert(rawget(lama.side, fuelSide),
    "The setting 'fuelSide' must be a valid lama.side.")

assert(rawget(lama.side, torchSide),
    "The setting 'torchSide' must be a valid lama.side.")

assert(rawget(lama.side, diskSide),
    "The setting 'diskSide' must be a valid lama.side.")

assert(dropSide ~= fuelSide and fuelSide ~= diskSide and
       dropSide ~= diskSide and diskSide ~= torchSide and
       dropSide ~= torchSide and fuelSide ~= torchSide,
       "Duplicate side configuration detected. Make sure the side for each " ..
       "docking bay element (disk, drop, fuel and torch chest) is different.")

assert(type(rsDiskSide) == "string" and rsDiskSide ~= "",
    "'rsDiskSide' is invalid; did you mess with the code?")

-------------------------------------------------------------------------------
-- Initialization                                                            --
-------------------------------------------------------------------------------

-- Command line argument parsing.
local args = {...}
if args[1] == "reset" then
    return private.reset()
elseif args[1] == "install" then
    if not private.reset() then
        return false
    end
elseif #args > 0 then
    print("Usage: jam [command]")
    print("Commands:")
    print("  reset   - resets the program state")
    print("            and formats the disk.")
    print("  install - resets and then runs JAM.")
    print()
    print("If no command is given, JAM is run")
    print("normally, either running the wizard")
    print("or resuming from a previous state.")
    return false
end

-- Make sure LAMA is initialized.
lama.init()

-- Run our program.
program:run()

-- If the program returns normally we've reached our final position, shut down.
os.shutdown()