'use strict';

const crypto = require('crypto');
const EventEmitter = require('events').EventEmitter;

class ImapNotifier extends EventEmitter {

    constructor(options) {
        super();

        this.database = options.database;

        let logfunc = (...args) => {
            let level = args.shift() || 'DEBUG';
            let message = args.shift() || '';

            console.log([level].concat(message || '').join(' '), ...args); // eslint-disable-line no-console
        };

        this.logger = options.logger || {
            info: logfunc.bind(null, 'INFO'),
            debug: logfunc.bind(null, 'DEBUG'),
            error: logfunc.bind(null, 'ERROR')
        };

        this._listeners = new EventEmitter();
        this._listeners.setMaxListeners(0);

        EventEmitter.call(this);
    }

    /**
     * Generates hashed event names for mailbox:username pairs
     *
     * @param {String} path
     * @param {String} username
     * @returns {String} md5 hex
     */
    _eventName(path, username) {
        return crypto.createHash('md5').update(username + ':' + path).digest('hex');
    }

    /**
     * Registers an event handler for path:username events
     *
     * @param {String} username
     * @param {String} path
     * @param {Function} handler Function to run once there are new entries in the journal
     */
    addListener(session, path, handler) {
        let eventName = this._eventName(session.user.username, path);
        this._listeners.addListener(eventName, handler);

        this.logger.debug('New journal listener for %s ("%s:%s")', eventName, session.user.username, path);
    }

    /**
     * Unregisters an event handler for path:username events
     *
     * @param {String} username
     * @param {String} path
     * @param {Function} handler Function to run once there are new entries in the journal
     */
    removeListener(session, path, handler) {
        let eventName = this._eventName(session.user.username, path);
        this._listeners.removeListener(eventName, handler);

        this.logger.debug('Removed journal listener from %s ("%s:%s")', eventName, session.user.username, path);
    }

    /**
     * Stores multiple journal entries to db
     *
     * @param {String} username
     * @param {String} path
     * @param {Array|Object} entries An array of entries to be journaled
     * @param {Function} callback Runs once the entry is either stored or an error occurred
     */
    addEntries(username, path, entries, callback) {
        if (entries && !Array.isArray(entries)) {
            entries = [entries];
        } else if (!entries || !entries.length) {
            return callback(null, false);
        }

        this.database.collection('mailboxes').findOneAndUpdate({
            username,
            path
        }, {
            $inc: {
                modifyIndex: entries.length
            }
        }, {}, (err, item) => {
            if (err) {
                return callback(err);
            }

            if (!item || !item.value) {
                // was not able to acquire a lock
                return callback(null, new Error('Selected mailbox does not exist'));
            }

            let mailbox = item.value;
            let startIndex = mailbox.modifyIndex;

            let updated = 0;
            let updateNext = () => {
                if (updated >= entries.length) {
                    return this.database.collection('journal').insertMany(entries, {
                        w: 1,
                        ordered: false
                    }, (err, r) => {
                        if (err) {
                            return callback(err);
                        }
                        return callback(null, r.insertedCount);
                    });
                }

                let entry = entries[updated++];

                entry.mailbox = mailbox._id;
                entry.modseq = ++startIndex;

                if (entry.message) {
                    this.database.collection('messages').findOneAndUpdate({
                        _id: entry.message,
                        modseq: {
                            $lt: entry.modseq
                        }
                    }, {
                        $set: {
                            modseq: entry.modseq
                        }
                    }, {}, err => {
                        if (err) {
                            this.logger.error('Error updating modseq for message %s. %s', entry.message, err.message);
                        }
                        updateNext();
                    });
                } else {
                    updateNext();
                }
            };

            updateNext();
        });
    }

    /**
     * Sends a notification that there are new updates in the selected mailbox
     *
     * @param {String} username
     * @param {String} path
     */
    fire(username, path, payload) {
        let eventName = this._eventName(username, path);
        setImmediate(() => {
            this._listeners.emit(eventName, payload);
        });
    }

    /**
     * Returns all entries from the journal that have higher than provided modification index
     *
     * @param {String} session
     * @param {String} path
     * @param {Number} modifyIndex Last known modification id
     * @param {Function} callback Returns update entries as an array
     */
    getUpdates(session, path, modifyIndex, callback) {
        modifyIndex = Number(modifyIndex) || 0;
        let username = session.user.username;

        this.database.collection('mailboxes').findOne({
            username,
            path
        }, (err, mailbox) => {
            if (err) {
                return callback(err);
            }
            if (!mailbox) {
                return callback(null, 'NONEXISTENT');
            }
            this.database.collection('journal').find({
                mailbox: mailbox._id,
                modseq: {
                    $gt: modifyIndex
                }
            }).toArray(callback);
        });
    }

}

module.exports = ImapNotifier;