Add implementation of now, sysdate, localtime and similar functions

common/src/main/java/org/opensearch/sql/common/utils/QueryContext.java

@@ -6,13 +6,16 @@
 
 package org.opensearch.sql.common.utils;
 
+import java.time.LocalDateTime;
 import java.util.Map;
 import java.util.Optional;
 import java.util.UUID;
 import org.apache.logging.log4j.ThreadContext;
 
 /**
  * Utility class for recording and accessing context for the query being executed.
+ * Implementation Details: context variables is being persisted statically in the thread context
+ * @see: @ThreadContext
  */
 public class QueryContext {
 

core/src/main/java/org/opensearch/sql/analysis/AnalysisContext.java

@@ -7,9 +7,12 @@
 package org.opensearch.sql.analysis;
 
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.Objects;
 import lombok.Getter;
+import org.opensearch.sql.expression.Expression;
 import org.opensearch.sql.expression.NamedExpression;
 
 /**
@@ -23,13 +26,26 @@ public class AnalysisContext {
   @Getter
   private final List<NamedExpression> namedParseExpressions;
 
+  /**
+   * Storage for values of functions which return a constant value.
+   * We are storing the values there to use it in sequential calls to those functions.
+   * For example, `now` function should the same value during processing a query.
+   */
+  @Getter
+  private final Map<String, Expression> constantFunctionValues;
+
   public AnalysisContext() {
     this(new TypeEnvironment(null));
   }
 
+  /**
+   * Class CTOR.
+   * @param environment Env to set to a new instance.
+   */
   public AnalysisContext(TypeEnvironment environment) {
     this.environment = environment;
     this.namedParseExpressions = new ArrayList<>();
+    this.constantFunctionValues = new HashMap<>();
   }
 
   /**

core/src/main/java/org/opensearch/sql/analysis/ExpressionAnalyzer.java

@@ -24,6 +24,7 @@
 import org.opensearch.sql.ast.expression.Case;
 import org.opensearch.sql.ast.expression.Cast;
 import org.opensearch.sql.ast.expression.Compare;
+import org.opensearch.sql.ast.expression.ConstantFunction;
 import org.opensearch.sql.ast.expression.EqualTo;
 import org.opensearch.sql.ast.expression.Field;
 import org.opensearch.sql.ast.expression.Function;
@@ -169,6 +170,19 @@ public Expression visitRelevanceFieldList(RelevanceFieldList node, AnalysisConte
         ImmutableMap.copyOf(node.getFieldList())));
   }
 
+  @Override
+  public Expression visitConstantFunction(ConstantFunction node, AnalysisContext context) {
+    var valueName = node.getFuncName();
+    if (context.getConstantFunctionValues().containsKey(valueName)) {
+      return context.getConstantFunctionValues().get(valueName);
+    }
+
+    var value = visitFunction(node, context);
+    value = DSL.literal(value.valueOf(null));
+    context.getConstantFunctionValues().put(valueName, value);
+    return value;
+  }
+
   @Override
   public Expression visitFunction(Function node, AnalysisContext context) {
     FunctionName functionName = FunctionName.of(node.getFuncName());

core/src/main/java/org/opensearch/sql/ast/AbstractNodeVisitor.java

@@ -15,6 +15,7 @@
 import org.opensearch.sql.ast.expression.Case;
 import org.opensearch.sql.ast.expression.Cast;
 import org.opensearch.sql.ast.expression.Compare;
+import org.opensearch.sql.ast.expression.ConstantFunction;
 import org.opensearch.sql.ast.expression.EqualTo;
 import org.opensearch.sql.ast.expression.Field;
 import org.opensearch.sql.ast.expression.Function;
@@ -116,6 +117,10 @@ public T visitRelevanceFieldList(RelevanceFieldList node, C context) {
     return visitChildren(node, context);
   }
 
+  public T visitConstantFunction(ConstantFunction node, C context) {
+    return visitChildren(node, context);
+  }
+
   public T visitUnresolvedAttribute(UnresolvedAttribute node, C context) {
     return visitChildren(node, context);
   }

core/src/main/java/org/opensearch/sql/ast/dsl/AstDSL.java

@@ -19,6 +19,7 @@
 import org.opensearch.sql.ast.expression.Case;
 import org.opensearch.sql.ast.expression.Cast;
 import org.opensearch.sql.ast.expression.Compare;
+import org.opensearch.sql.ast.expression.ConstantFunction;
 import org.opensearch.sql.ast.expression.DataType;
 import org.opensearch.sql.ast.expression.EqualTo;
 import org.opensearch.sql.ast.expression.Field;
@@ -234,6 +235,10 @@ public static Function function(String funcName, UnresolvedExpression... funcArg
     return new Function(funcName, Arrays.asList(funcArgs));
   }
 
+  public static Function constantFunction(String funcName, UnresolvedExpression... funcArgs) {
+    return new ConstantFunction(funcName, Arrays.asList(funcArgs));
+  }
+
   /**
    * CASE
    *     WHEN search_condition THEN result_expr

core/src/main/java/org/opensearch/sql/ast/expression/ConstantFunction.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+
+package org.opensearch.sql.ast.expression;
+
+import java.util.List;
+import lombok.EqualsAndHashCode;
+import org.opensearch.sql.ast.AbstractNodeVisitor;
+
+/**
+ * Expression node that holds a function which should be replaced by its constant[1] value.
+ * [1] Constant at execution time.
+ */
+@EqualsAndHashCode(callSuper = false)
+public class ConstantFunction extends Function {
+
+  public ConstantFunction(String funcName, List<UnresolvedExpression> funcArgs) {
+    super(funcName, funcArgs);
+  }
+
+  @Override
+  public <R, C> R accept(AbstractNodeVisitor<R, C> nodeVisitor, C context) {
+    return nodeVisitor.visitConstantFunction(this, context);
+  }
+}

core/src/main/java/org/opensearch/sql/expression/DSL.java

@@ -682,6 +682,42 @@ public FunctionExpression match_bool_prefix(Expression... args) {
     return compile(BuiltinFunctionName.MATCH_BOOL_PREFIX, args);
   }
 
+  public FunctionExpression now(Expression... args) {
+    return compile(BuiltinFunctionName.NOW, args);
+  }
+
+  public FunctionExpression current_timestamp(Expression... args) {
+    return compile(BuiltinFunctionName.CURRENT_TIMESTAMP, args);
+  }
+
+  public FunctionExpression localtimestamp(Expression... args) {
+    return compile(BuiltinFunctionName.LOCALTIMESTAMP, args);
+  }
+
+  public FunctionExpression localtime(Expression... args) {
+    return compile(BuiltinFunctionName.LOCALTIME, args);
+  }
+
+  public FunctionExpression sysdate(Expression... args) {
+    return compile(BuiltinFunctionName.SYSDATE, args);
+  }
+
+  public FunctionExpression curtime(Expression... args) {
+    return compile(BuiltinFunctionName.CURTIME, args);
+  }
+
+  public FunctionExpression current_time(Expression... args) {
+    return compile(BuiltinFunctionName.CURRENT_TIME, args);
+  }
+
+  public FunctionExpression curdate(Expression... args) {
+    return compile(BuiltinFunctionName.CURDATE, args);
+  }
+
+  public FunctionExpression current_date(Expression... args) {
+    return compile(BuiltinFunctionName.CURRENT_DATE, args);
+  }
+
   private FunctionExpression compile(BuiltinFunctionName bfn, Expression... args) {
     return (FunctionExpression) repository.compile(bfn.getName(), Arrays.asList(args.clone()));
   }

core/src/main/java/org/opensearch/sql/expression/datetime/DateTimeFunction.java

@@ -19,12 +19,16 @@
 import static org.opensearch.sql.expression.function.FunctionDSL.impl;
 import static org.opensearch.sql.expression.function.FunctionDSL.nullMissingHandling;
 
+import java.math.BigDecimal;
+import java.math.RoundingMode;
 import java.time.LocalDate;
+import java.time.LocalDateTime;
 import java.time.LocalTime;
 import java.time.format.DateTimeFormatter;
 import java.time.format.TextStyle;
 import java.util.Locale;
 import java.util.concurrent.TimeUnit;
+import javax.annotation.Nullable;
 import lombok.experimental.UtilityClass;
 import org.opensearch.sql.data.model.ExprDateValue;
 import org.opensearch.sql.data.model.ExprDatetimeValue;
@@ -85,6 +89,84 @@ public void register(BuiltinFunctionRepository repository) {
     repository.register(to_days());
     repository.register(week());
     repository.register(year());
+
+    repository.register(now());
+    repository.register(current_timestamp());
+    repository.register(localtimestamp());
+    repository.register(localtime());
+    repository.register(sysdate());
+    repository.register(curtime());
+    repository.register(current_time());
+    repository.register(curdate());
+    repository.register(current_date());
+  }
+
+  /**
+   * NOW() returns a constant time that indicates the time at which the statement began to execute.
+   * `fsp` argument support is removed until refactoring to avoid bug where `now()`, `now(x)` and
+   * `now(y) return different values.
+   */
+  private FunctionResolver now(FunctionName functionName) {
+    return define(functionName,
+        impl(() -> new ExprDatetimeValue(formatNow(null)), DATETIME)
+    );
+  }
+
+  private FunctionResolver now() {
+    return now(BuiltinFunctionName.NOW.getName());
+  }
+
+  private FunctionResolver current_timestamp() {
+    return now(BuiltinFunctionName.CURRENT_TIMESTAMP.getName());
+  }
+
+  private FunctionResolver localtimestamp() {
+    return now(BuiltinFunctionName.LOCALTIMESTAMP.getName());
+  }
+
+  private FunctionResolver localtime() {
+    return now(BuiltinFunctionName.LOCALTIME.getName());
+  }
+
+  /**
+   * SYSDATE() returns the time at which it executes.
+   */
+  private FunctionResolver sysdate() {
+    return define(BuiltinFunctionName.SYSDATE.getName(),
+        impl(() -> new ExprDatetimeValue(formatNow(null)), DATETIME),
+        impl((v) -> new ExprDatetimeValue(formatNow(v.integerValue())), DATETIME, INTEGER)
+    );
+  }
+
+  /**
+   * Synonym for @see `now`.
+   */
+  private FunctionResolver curtime(FunctionName functionName) {
+    return define(functionName,
+        impl(() -> new ExprTimeValue(formatNow(null).toLocalTime()), TIME)
+    );
+  }
+
+  private FunctionResolver curtime() {
+    return curtime(BuiltinFunctionName.CURTIME.getName());
+  }
+
+  private FunctionResolver current_time() {
+    return curtime(BuiltinFunctionName.CURRENT_TIME.getName());
+  }
+
+  private FunctionResolver curdate(FunctionName functionName) {
+    return define(functionName,
+        impl(() -> new ExprDateValue(formatNow(null).toLocalDate()), DATE)
+    );
+  }
+
+  private FunctionResolver curdate() {
+    return curdate(BuiltinFunctionName.CURDATE.getName());
+  }
+
+  private FunctionResolver current_date() {
+    return curdate(BuiltinFunctionName.CURRENT_DATE.getName());
   }
 
   /**
@@ -742,4 +824,24 @@ private ExprValue exprYear(ExprValue date) {
     return new ExprIntegerValue(date.dateValue().getYear());
   }
 
+  /**
+   * Prepare LocalDateTime value. Truncate fractional second part according to the argument.
+   * @param fsp argument is given to specify a fractional seconds precision from 0 to 6,
+   *            the return value includes a fractional seconds part of that many digits.
+   * @return LocalDateTime object.
+   */
+  private LocalDateTime formatNow(@Nullable Integer fsp) {
+    var res = LocalDateTime.now();
+    if (fsp == null) {
+      fsp = 0;
+    }
+    var defaultPrecision = 9; // There are 10^9 nanoseconds in one second
+    if (fsp < 0 || fsp > 6) { // Check that the argument is in the allowed range [0, 6]
+      throw new IllegalArgumentException(
+          String.format("Invalid `fsp` value: %d, allowed 0 to 6", fsp));
+    }
+    var nano = new BigDecimal(res.getNano())
+        .setScale(fsp - defaultPrecision, RoundingMode.DOWN).intValue();
+    return res.withNano(nano);
+  }
 }

core/src/main/java/org/opensearch/sql/expression/function/BuiltinFunctionName.java

@@ -84,7 +84,16 @@ public enum BuiltinFunctionName {
   TO_DAYS(FunctionName.of("to_days")),
   WEEK(FunctionName.of("week")),
   YEAR(FunctionName.of("year")),
-
+  // `now`-like functions
+  NOW(FunctionName.of("now")),
+  CURDATE(FunctionName.of("curdate")),
+  CURRENT_DATE(FunctionName.of("current_date")),
+  CURTIME(FunctionName.of("curtime")),
+  CURRENT_TIME(FunctionName.of("current_time")),
+  LOCALTIME(FunctionName.of("localtime")),
+  CURRENT_TIMESTAMP(FunctionName.of("current_timestamp")),
+  LOCALTIMESTAMP(FunctionName.of("localtimestamp")),
+  SYSDATE(FunctionName.of("sysdate")),
   /**
    * Text Functions.
    */