/**
 *    Copyright (C) 2015 MongoDB Inc.
 *
 *    This program is free software: you can redistribute it and/or  modify
 *    it under the terms of the GNU Affero General Public License, version 3,
 *    as published by the Free Software Foundation.
 *
 *    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
 *    GNU Affero General Public License for more details.
 *
 *    You should have received a copy of the GNU Affero General Public License
 *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *    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 GNU Affero General 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 <memory>
#include <string>
#include <utility>
#include <vector>

#include "mongo/base/disallow_copying.h"
#include "mongo/base/status.h"
#include "mongo/base/status_with.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/repl/oplog_entry.h"
#include "mongo/db/repl/replication_executor.h"
#include "mongo/stdx/condition_variable.h"
#include "mongo/stdx/functional.h"
#include "mongo/stdx/mutex.h"

namespace mongo {
namespace repl {

class Applier {
    MONGO_DISALLOW_COPYING(Applier);

public:
    /**
     * Operations sorted by timestamp in ascending order.
     */
    using Operations = std::vector<OplogEntry>;

    /**
     * Callback function to report final status of applying operations along with
     * list of operations (if applicable) that were not successfully applied.
     * On success, returns the timestamp of the last operation applied together with an empty
     * list of operations.
     */
    using CallbackFn = stdx::function<void(const StatusWith<Timestamp>&, const Operations&)>;

    /**
     * Type of function to to apply a single operation. In production, this function
     * would have the same outcome as calling SyncTail::syncApply() ('convertUpdatesToUpserts'
     * value will be embedded in the function implementation).
     */
    using ApplyOperationFn = stdx::function<Status(OperationContext*, const OplogEntry&)>;

    /**
     * Creates Applier in inactive state.
     *
     * Accepts list of oplog entries to apply in 'operations'.
     *
     * The callback function will be invoked (after schedule()) when the applied has
     * successfully applied all the operations or encountered a failure. Failures may occur if
     * we failed to apply an operation; or if the underlying scheduled work item
     * on the replication executor was canceled.
     *
     * It is an error for 'operations' to be empty but individual oplog entries
     * contained in 'operations' are not validated.
     */
    Applier(ReplicationExecutor* executor,
            const Operations& operations,
            const ApplyOperationFn& applyOperation,
            const CallbackFn& onCompletion);

    /**
     * Blocks while applier is active.
     */
    virtual ~Applier();

    /**
     * Returns diagnostic information.
     */
    std::string getDiagnosticString() const;

    /**
     * Returns true if the applier has been started (but has not completed).
     */
    bool isActive() const;

    /**
     * Starts applier by scheduling initial db work to be run by the executor.
     */
    Status start();

    /**
     * Cancels current db work request.
     * Returns immediately if applier is not active.
     *
     * Callback function may be invoked with an ErrorCodes::CallbackCanceled status.
     */
    void cancel();

    /**
     * Waits for active database worker to complete.
     * Returns immediately if applier is not active.
     */
    void wait();

private:
    /**
     * DB worker callback function - applies all operations.
     */
    void _callback(const ReplicationExecutor::CallbackArgs& cbd);
    void _finishCallback(const StatusWith<Timestamp>& result, const Operations& operations);

    // Not owned by us.
    ReplicationExecutor* _executor;

    Operations _operations;
    ApplyOperationFn _applyOperation;
    CallbackFn _onCompletion;

    // Protects member data of this Applier.
    mutable stdx::mutex _mutex;

    stdx::condition_variable _condition;

    // _active is true when Applier is scheduled to be run by the executor.
    bool _active;

    ReplicationExecutor::CallbackHandle _dbWorkCallbackHandle;
};


/**
 * Applies operations (sorted by timestamp) up to and including 'lastTimestampToApply'.
 * If 'lastTimestampToApply' is found in  'operations':
 *     - The applier will be given a subset of 'operations' (includes 'lastTimestampToApply').
 *     - On success, the applier will invoke the 'pause' function just before reporting
 *       completion status.
 * Otherwise, all entries in 'operations' before 'lastTimestampToApply' will be forwarded to
 * the applier and the 'pause' function will be ignored.
 * If the applier is successfully created, returns the applier and a list of operations that
 * are skipped (operations with 'ts' field value after 'lastTimestampToApply).
 */
using PauseDataReplicatorFn = stdx::function<void()>;

StatusWith<std::pair<std::unique_ptr<Applier>, Applier::Operations>> applyUntilAndPause(
    ReplicationExecutor* executor,
    const Applier::Operations& operations,
    const Applier::ApplyOperationFn& applyOperation,
    const Timestamp& lastTimestampToApply,
    const PauseDataReplicatorFn& pauseDataReplicator,
    const Applier::CallbackFn& onCompletion);

}  // namespace repl
}  // namespace mongo