// # Update Database
// Handles migrating a database between two different database versions
var Promise = require('bluebird'),
    _ = require('lodash'),
    backup = require('./backup'),
    fixtures = require('./fixtures'),
    errors = require('../../errors'),
    logging = require('../../logging'),
    i18n = require('../../i18n'),
    db = require('../../data/db'),
    versioning = require('../schema').versioning,
    sequence = function sequence(tasks, modelOptions, logger) {
        // utils/sequence.js does not offer an option to pass cloned arguments
        return Promise.reduce(tasks, function (results, task) {
            return task(_.cloneDeep(modelOptions), logger)
                .then(function (result) {
                    results.push(result);
                    return results;
                });
        }, []);
    },
    updateDatabaseSchema,
    migrateToDatabaseVersion,
    execute, logger, isDatabaseOutOfDate;

logger = {
    info: function info(message) {
        logging.info('Migrations:' + message);
    },
    warn: function warn(message) {
        logging.warn('Skipping Migrations:' + message);
    }
};

/**
 * update database schema for one single version
 */
updateDatabaseSchema = function (tasks, logger, modelOptions) {
    if (!tasks.length) {
        return Promise.resolve();
    }

    return sequence(tasks, modelOptions, logger);
};

/**
 * update each database version as one transaction
 * if a version fails, rollback
 * if a version fails, stop updating more versions
 */
migrateToDatabaseVersion = function migrateToDatabaseVersion(version, logger, modelOptions) {
    return new Promise(function (resolve, reject) {
        db.knex.transaction(function (transaction) {
            var migrationTasks = versioning.getUpdateDatabaseTasks(version, logger),
                fixturesTasks = versioning.getUpdateFixturesTasks(version, logger);

            logger.info('Updating database to ' + version);

            modelOptions.transacting = transaction;

            updateDatabaseSchema(migrationTasks, logger, modelOptions)
                .then(function () {
                    return fixtures.update(fixturesTasks, logger, modelOptions);
                })
                .then(function () {
                    return versioning.setDatabaseVersion(transaction, version);
                })
                .then(function () {
                    transaction.commit();
                    resolve();
                })
                .catch(function (err) {
                    logger.warn('rolling back because of: ' + err.stack);

                    transaction.rollback();
                });
        }).catch(function () {
            reject();
        });
    });
};

/**
 * ## Update
 * Does a backup, then updates the database and fixtures
 */
execute = function execute(options) {
    options = options || {};

    var fromVersion = options.fromVersion,
        toVersion = options.toVersion,
        forceMigration = options.forceMigration,
        versionsToUpdate,
        modelOptions = {
            context: {
                internal: true
            }
        };

    fromVersion = forceMigration ? versioning.canMigrateFromVersion : fromVersion;

    // Figure out which versions we're updating through.
    // This shouldn't include the from/current version (which we're already on)
    versionsToUpdate = versioning.getMigrationVersions(fromVersion, toVersion).slice(1);

    return backup(logger)
        .then(function () {
            logger.info('Migration required from ' + fromVersion + ' to ' + toVersion);
            return Promise.mapSeries(versionsToUpdate, function (versionToUpdate) {
                return migrateToDatabaseVersion(versionToUpdate, logger, modelOptions);
            });
        })
        .then(function () {
            logger.info('Finished!');
        });
};

isDatabaseOutOfDate = function isDatabaseOutOfDate(options) {
    options = options || {};

    var fromVersion = options.fromVersion,
        toVersion = options.toVersion,
        forceMigration = options.forceMigration;

    // CASE: current database version is lower then we support
    if (fromVersion < versioning.canMigrateFromVersion) {
        return {
            error: new errors.DatabaseVersionError({
                message: i18n.t('errors.data.versioning.index.cannotMigrate.error'),
                context: i18n.t('errors.data.versioning.index.cannotMigrate.context'),
                help: i18n.t('common.seeLinkForInstructions', {link: 'http://support.ghost.org/how-to-upgrade/'})
            })
        };
    }
    // CASE: the database exists but is out of date
    else if (fromVersion < toVersion || forceMigration) {
        return {migrate: true};
    }
    // CASE: database is up-to-date
    else if (fromVersion === toVersion) {
        return {migrate: false};
    }
    // CASE: we don't understand the version
    else {
        return {error: new errors.DatabaseVersionError({message: i18n.t('errors.data.versioning.index.dbVersionNotRecognized')})};
    }
};

exports.execute = execute;
exports.isDatabaseOutOfDate = isDatabaseOutOfDate;