/*
    * SPDX-FileCopyrightText: none
    * SPDX-License-Identifier: CC0-1.0
    */
   
   package dev.metaschema.core.metapath.cst.logic;
   
   import dev.metaschema.core.metapath.DynamicContext;
   import dev.metaschema.core.metapath.IExpression;
  import dev.metaschema.core.metapath.cst.IExpressionVisitor;
  import dev.metaschema.core.metapath.function.ComparisonFunctions;
  import dev.metaschema.core.metapath.item.ISequence;
  import dev.metaschema.core.metapath.item.atomic.IAnyAtomicItem;
  import dev.metaschema.core.metapath.item.atomic.IBooleanItem;
  import edu.umd.cs.findbugs.annotations.NonNull;
  import edu.umd.cs.findbugs.annotations.Nullable;
  
  /**
   * Supports Metapath
   * <a href="https://www.w3.org/TR/xpath-31/#id-value-comparisons">value
   * comparisons</a>.
   */
  public class ValueComparison
      extends AbstractComparison {
  
    /**
     * Create a new value comparison expression.
     *
     * @param text
     *          the parsed text of the expression
     * @param left
     *          the expression to compare against
     * @param operator
     *          the comparison operator
     * @param right
     *          the expression to compare with
     */
    public ValueComparison(
        @NonNull String text,
        @NonNull IExpression left,
        @NonNull ComparisonFunctions.Operator operator,
        @NonNull IExpression right) {
      super(text, left, operator, right);
    }
  
    @Override
    public <RESULT, CONTEXT> RESULT accept(IExpressionVisitor<RESULT, CONTEXT> visitor, CONTEXT context) {
      return visitor.visitValueComparison(this, context);
    }
  
    @Override
    protected ISequence<? extends IBooleanItem> evaluate(DynamicContext dynamicContext, ISequence<?> focus) {
      IAnyAtomicItem left = ISequence.of(getLeft().accept(dynamicContext, focus).atomize()).getFirstItem(false);
      IAnyAtomicItem right = ISequence.of(getRight().accept(dynamicContext, focus).atomize()).getFirstItem(false);
      return resultOrEmpty(left, right, dynamicContext);
    }
  
    /**
     * Compare the two atomic items.
     *
     * @param leftItem
     *          the first item to compare
     * @param rightItem
     *          the second item to compare
     * @param dynamicContext
     *          used to get the implicit timezone from the evaluation context
     * @return a or an empty {@link ISequence} if either item is {@code null}
     */
    @NonNull
    private ISequence<? extends IBooleanItem> resultOrEmpty(
        @Nullable IAnyAtomicItem leftItem,
        @Nullable IAnyAtomicItem rightItem,
        @NonNull DynamicContext dynamicContext) {
      ISequence<? extends IBooleanItem> retval;
      if (leftItem == null || rightItem == null) {
        retval = ISequence.empty();
      } else {
        IBooleanItem result = ComparisonFunctions.valueCompairison(leftItem, getOperator(), rightItem, dynamicContext);
        retval = ISequence.of(result);
      }
      return retval;
    }
  }