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package net.thisptr.jackson.jq.internal.tree;

import java.util.ArrayList;
import java.util.List;
import java.util.Stack;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.node.NullNode;

import net.thisptr.jackson.jq.Expression;
import net.thisptr.jackson.jq.PathOutput;
import net.thisptr.jackson.jq.Scope;
import net.thisptr.jackson.jq.exception.JsonQueryException;
import net.thisptr.jackson.jq.internal.misc.Pair;
import net.thisptr.jackson.jq.internal.tree.matcher.PatternMatcher;
import net.thisptr.jackson.jq.path.Path;

public class ReduceExpression implements Expression {
	private Expression iterExpr;
	private Expression reduceExpr;
	private Expression initExpr;
	private PatternMatcher matcher;

	public ReduceExpression(final PatternMatcher matcher, final Expression initExpr, final Expression reduceExpr, final Expression iterExpr) {
		this.matcher = matcher;
		this.initExpr = initExpr;
		this.reduceExpr = reduceExpr;
		this.iterExpr = iterExpr;
	}

	// reduce iterExpr as matcher (initExpr; reduceExpr)

	@Override
	public void apply(final Scope scope, final JsonNode in, final Path ipath, final PathOutput output, final boolean requirePath) throws JsonQueryException {
		initExpr.apply(scope, in, (accumulator) -> {
			// Wrap in array to allow mutation inside lambda
			final JsonNode[] accumulators = new JsonNode[] { accumulator };

			final Scope childScope = Scope.newChildScope(scope);
			iterExpr.apply(scope, in, (item) -> {
				final Stack> stack = new Stack<>();
				matcher.match(scope, item, (final List> vars) -> {
					for (int i = vars.size() - 1; i >= 0; --i) {
						final Pair var = vars.get(i);
						childScope.setValue(var._1, var._2);
					}

					// We only use the last value from reduce expression.
					final List reduceResult = new ArrayList<>();
					reduceExpr.apply(childScope, accumulators[0], reduceResult::add);
					accumulators[0] = reduceResult.isEmpty() ? NullNode.getInstance() : reduceResult.get(reduceResult.size() - 1);
				}, stack);
			});

			output.emit(accumulators[0], null);
		});
	}

	@Override
	public String toString() {
		return String.format("(reduce %s as %s (%s; %s))", iterExpr, matcher, initExpr, reduceExpr);
	}
}