'use strict';

const _ = require('lodash')
const async = require('async')
const deepExtend = require('deep-extend')
const moment = require('moment')

const config = require('../config').config
const Database = require('../db/database').db
const Logger = require('../logger')
const MailTemplateService = require('./mailTemplateService')
const Resources = require('../utils/resources')

const MAIL_QUEUE_DB_BATCH_SIZE = 50;
const MAIL_QUEUE_MAX_PARALLEL_SENDING = 3;

const transporter = require('nodemailer').createTransport(deepExtend(
    {},
    config.server.email.smtp,
    {
        transport: 'smtp',
        pool: true
    }
));

MailTemplateService.configureTransporter(transporter);

function sendMail(options, callback) {
    Logger
        .tag('mail', 'queue')
        .info(
            'Sending pending mail[%d] of type %s. ' +
            'Had %d failures before.',
            options.id, options.email, options.failures
        );

    MailTemplateService.render(options, function (err, renderedTemplate) {
            if (err) {
                return callback(err);
            }

            const mailOptions = {
                from: options.sender,
                to: options.recipient,
                subject: renderedTemplate.subject,
                html: renderedTemplate.body
            };

            transporter.sendMail(mailOptions, function (err) {
                if (err) {
                    return callback(err);
                }

                Logger.tag('mail', 'queue').info('Mail[%d] has been send.', options.id);

                callback(null);
            });
        }
    );
}

function findPendingMailsBefore(beforeMoment, limit, callback) {
    Database.all(
        'SELECT * FROM email_queue WHERE modified_at < ? AND failures < ? ORDER BY id ASC LIMIT ?',
        [beforeMoment.unix(), 5, limit],
        function (err, rows) {
            if (err) {
                return callback(err);
            }

            let pendingMails;
            try {
                pendingMails = _.map(rows, function (row) {
                    return deepExtend(
                        {},
                        row,
                        {
                            data: JSON.parse(row.data)
                        }
                    );
                });
            }
            catch (error) {
                return callback(error);
            }

            callback(null, pendingMails);
        }
    );
}

function removePendingMailFromQueue(id, callback) {
    Database.run('DELETE FROM email_queue WHERE id = ?', [id], callback);
}

function incrementFailureCounterForPendingEmail(id, callback) {
    const now = moment();
    Database.run(
        'UPDATE email_queue SET failures = failures + 1, modified_at = ? WHERE id = ?',
        [now.unix(), id],
        callback
    );
}

function sendPendingMail(pendingMail, callback) {
    sendMail(pendingMail, function (err) {
        if (err) {
            // we only log the error and increment the failure counter as we want to continue with pending mails
            Logger.tag('mail', 'queue').error('Error sending pending mail[' + pendingMail.id + ']:', err);

            return incrementFailureCounterForPendingEmail(pendingMail.id, function (err) {
                if (err) {
                    return callback(err);
                }
                return callback(null);
            });
        }

        removePendingMailFromQueue(pendingMail.id, callback);
    });
}

function doGetMail(id, callback) {
    Database.get('SELECT * FROM email_queue WHERE id = ?', [id], callback);
}

module.exports = {
    enqueue (sender, recipient, email, data, callback) {
        if (!_.isPlainObject(data)) {
            return callback(new Error('Unexpected data: ' + data));
        }
        Database.run(
            'INSERT INTO email_queue ' +
            '(failures, sender, recipient, email, data) ' +
            'VALUES (?, ?, ?, ?, ?)',
            [0, sender, recipient, email, JSON.stringify(data)],
            function (err, res) {
                callback(err, res);
            }
        );
    },

    getMail (id, callback) {
        doGetMail(id, callback);
    },

    getPendingMails (restParams, callback) {
        Database.get(
            'SELECT count(*) AS total FROM email_queue',
            [],
            function (err, row) {
                if (err) {
                    return callback(err);
                }

                const total = row.total;

                const filter = Resources.filterClause(
                    restParams,
                    'id',
                    ['id', 'failures', 'sender', 'recipient', 'email', 'created_at', 'modified_at'],
                    ['id', 'failures', 'sender', 'recipient', 'email']
                );

                Database.all(
                    'SELECT * FROM email_queue WHERE ' + filter.query,
                    _.concat([], filter.params),
                    function (err, rows) {
                        if (err) {
                            return callback(err);
                        }

                        callback(null, rows, total);
                    }
                );
            }
        );
    },

    deleteMail (id, callback) {
        removePendingMailFromQueue(id, callback);
    },

    resetFailures (id, callback) {
        Database.run(
            'UPDATE email_queue SET failures = 0, modified_at = ? WHERE id = ?',
            [moment().unix(), id],
            function (err) {
                if (err) {
                    return callback(err);
                }

                if (!this.changes) {
                    return callback('Error: could not reset failure count for mail: ' + id);
                }

                doGetMail(id, callback);
            }
        );
    },

    sendPendingMails (callback) {
        Logger.tag('mail', 'queue').debug('Start sending pending mails...');

        const startTime = moment();

        const sendNextBatch = function (err) {
            if (err) {
                return callback(err);
            }

            Logger.tag('mail', 'queue').debug('Sending next batch...');

            findPendingMailsBefore(startTime, MAIL_QUEUE_DB_BATCH_SIZE, function (err, pendingMails) {
                if (err) {
                    return callback(err);
                }

                if (_.isEmpty(pendingMails)) {
                    Logger.tag('mail', 'queue').debug('Done sending pending mails.');
                    return callback(null);
                }

                async.eachLimit(
                    pendingMails,
                    MAIL_QUEUE_MAX_PARALLEL_SENDING,
                    sendPendingMail,
                    sendNextBatch
                );
            });
        };

        sendNextBatch(null);
    }
}