/**
 *    Copyright (C) 2019-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#pragma once

#include "mongo/db/pipeline/expression.h"
#include "mongo/db/pipeline/javascript_execution.h"

namespace mongo {

/**
 * This expression takes in a JavaScript function and a "this" reference, and returns an array of
 * key/value objects which are the results of calling emit() from the provided JS function.
 */
class ExpressionInternalJsEmit final : public Expression {
public:
    static constexpr auto kExpressionName = "$_internalJsEmit"_sd;

    static boost::intrusive_ptr<Expression> parse(ExpressionContext* expCtx,
                                                  BSONElement expr,
                                                  const VariablesParseState& vps);

    static boost::intrusive_ptr<ExpressionInternalJsEmit> create(
        ExpressionContext* const expCtx,
        boost::intrusive_ptr<Expression> thisRef,
        std::string funcSourceString) {
        return new ExpressionInternalJsEmit{expCtx, thisRef, std::move(funcSourceString)};
    }

    Value evaluate(const Document& root, Variables* variables) const final;

    Value serialize(bool explain) const final;

    void acceptVisitor(ExpressionMutableVisitor* visitor) final {
        return visitor->visit(this);
    }

    void acceptVisitor(ExpressionConstVisitor* visitor) const final {
        return visitor->visit(this);
    }

    // For a given invocation of the user-defined function, this struct holds the results of each
    // call to emit(). Mark as mutable since it needs to be modified for each call to evaluate().
    mutable struct EmitState {
        void emit(Document&& doc) {
            bytesUsed += doc.getApproximateSize();
            uassert(31292,
                    str::stream() << "Size of emitted values exceeds the set size limit of "
                                  << byteLimit << " bytes",
                    bytesUsed < byteLimit);
            emittedObjects.emplace_back(std::move(doc));
        }

        auto reset() {
            emittedObjects.clear();
            bytesUsed = 0;
        }

        std::vector<Value> emittedObjects;
        int byteLimit;
        int bytesUsed;
    } _emitState;

private:
    ExpressionInternalJsEmit(ExpressionContext* expCtx,
                             boost::intrusive_ptr<Expression> thisRef,
                             std::string funcSourceString);

    void _doAddDependencies(DepsTracker* deps) const final override;

    const boost::intrusive_ptr<Expression>& _thisRef;
    std::string _funcSource;
};
}  // namespace mongo