/*
    * SPDX-FileCopyrightText: none
    * SPDX-License-Identifier: CC0-1.0
    */
   
   package dev.metaschema.core.metapath.cst.items;
   
   import java.util.List;
   
  import dev.metaschema.core.metapath.DynamicContext;
  import dev.metaschema.core.metapath.IExpression;
  import dev.metaschema.core.metapath.cst.IExpressionVisitor;
  import dev.metaschema.core.metapath.item.ICollectionValue;
  import dev.metaschema.core.metapath.item.IItem;
  import dev.metaschema.core.metapath.item.ISequence;
  import dev.metaschema.core.metapath.item.function.IArrayItem;
  import dev.metaschema.core.metapath.item.function.IKeySpecifier;
  import dev.metaschema.core.metapath.item.function.IMapItem;
  import dev.metaschema.core.util.ObjectUtils;
  import edu.umd.cs.findbugs.annotations.NonNull;
  
  /**
   * An implementation of
   * <a href="https://www.w3.org/TR/xpath-31/#id-unary-lookup">Unary Lookup
   * Operators</a> supporting access to items in Metapath maps and arrays.
   * <p>
   * Provides support for various types of key- and index-based lookups related to
   * {@link IMapItem} and {@link IArrayItem} objects.
   */
  public class UnaryLookup
      extends AbstractLookup {
    /**
     * Construct a new unary lookup expression that uses the provided key specifier.
     *
     * @param text
     *          the parsed text of the expression
     * @param keySpecifier
     *          the key specifier used to determine matching entries
     */
    public UnaryLookup(@NonNull String text, @NonNull IKeySpecifier keySpecifier) {
      super(text, keySpecifier);
    }
  
    @SuppressWarnings("null")
    @Override
    public List<? extends IExpression> getChildren() {
      return List.of();
    }
  
    @Override
    protected ISequence<? extends IItem> evaluate(DynamicContext dynamicContext, ISequence<?> focus) {
      IKeySpecifier specifier = getKeySpecifier();
  
      return ISequence.of(ObjectUtils.notNull(focus.stream()
          .flatMap(item -> {
            assert item != null;
            return specifier.lookup(item, dynamicContext, focus);
          })
          .flatMap(ICollectionValue::normalizeAsItems)));
    }
  
    @Override
    public <RESULT, CONTEXT> RESULT accept(@NonNull IExpressionVisitor<RESULT, CONTEXT> visitor, CONTEXT context) {
      return visitor.visitUnaryLookup(this, context);
    }
  }