"use strict";

// external modules
var Sequelize = require("sequelize");
var LZString = require('lz-string');
var async = require('async');
var moment = require('moment');
var childProcess = require('child_process');
var shortId = require('shortid');

// core
var config = require("../config.js");
var logger = require("../logger.js");

var dmpWorker = createDmpWorker();
var dmpCallbackCache = {};

function createDmpWorker() {
    var worker = childProcess.fork("./lib/workers/dmpWorker.js", {
        stdio: 'ignore'
    });
    if (config.debug) logger.info('dmp worker process started');
    worker.on('message', function (data) {
        if (!data || !data.msg || !data.cacheKey) {
            return logger.error('dmp worker error: not enough data on message');
        }
        var cacheKey = data.cacheKey;
        switch(data.msg) {
            case 'error':
                dmpCallbackCache[cacheKey](data.error, null);
                break;
            case 'check':
                dmpCallbackCache[cacheKey](null, data.result);
                break;
        }
        delete dmpCallbackCache[cacheKey];
    });
    worker.on('close', function (code) {
        dmpWorker = null;
        if (config.debug) logger.info('dmp worker process exited with code ' + code);
    });
    return worker;
}

function sendDmpWorker(data, callback) {
    if (!dmpWorker) dmpWorker = createDmpWorker();
    var cacheKey = Date.now() + '_' + shortId.generate();
    dmpCallbackCache[cacheKey] = callback;
    data = Object.assign(data, {
        cacheKey: cacheKey
    });
    dmpWorker.send(data);
}

module.exports = function (sequelize, DataTypes) {
    var Revision = sequelize.define("Revision", {
        id: {
            type: DataTypes.UUID,
            primaryKey: true,
            defaultValue: Sequelize.UUIDV4
        },
        patch: {
            type: DataTypes.TEXT
        },
        lastContent: {
            type: DataTypes.TEXT
        },
        content: {
            type: DataTypes.TEXT
        },
        length: {
            type: DataTypes.INTEGER
        },
        authorship: {
            type: DataTypes.TEXT
        }
    }, {
        classMethods: {
            associate: function (models) {
                Revision.belongsTo(models.Note, {
                    foreignKey: "noteId",
                    as: "note",
                    constraints: false
                });
            },
            getNoteRevisions: function (note, callback) {
                Revision.findAll({
                    where: {
                        noteId: note.id
                    },
                    order: '"createdAt" DESC'
                }).then(function (revisions) {
                    var data = [];
                    for (var i = 0, l = revisions.length; i < l; i++) {
                        var revision = revisions[i];
                        data.push({
                            time: moment(revision.createdAt).valueOf(),
                            length: revision.length
                        });
                    }
                    callback(null, data);
                }).catch(function (err) {
                    callback(err, null);
                });
            },
            getPatchedNoteRevisionByTime: function (note, time, callback) {
                // find all revisions to prepare for all possible calculation
                Revision.findAll({
                    where: {
                        noteId: note.id
                    },
                    order: '"createdAt" DESC'
                }).then(function (revisions) {
                    if (revisions.length <= 0) return callback(null, null);
                    // measure target revision position 
                    Revision.count({
                        where: {
                            noteId: note.id,
                            createdAt: {
                                $gte: time
                            }
                        },
                        order: '"createdAt" DESC'
                    }).then(function (count) {
                        if (count <= 0) return callback(null, null);
                        sendDmpWorker({
                            msg: 'get revision',
                            revisions: revisions,
                            count: count
                        }, callback);
                    }).catch(function (err) {
                        return callback(err, null);
                    });
                }).catch(function (err) {
                    return callback(err, null);
                });
            },
            checkAllNotesRevision: function (callback) {
                Revision.saveAllNotesRevision(function (err, notes) {
                    if (err) return callback(err, null);
                    if (!notes || notes.length <= 0) {
                        return callback(null, notes);
                    } else {
                        Revision.checkAllNotesRevision(callback);
                    }
                });
            },
            saveAllNotesRevision: function (callback) {
                sequelize.models.Note.findAll({
                    // query all notes that need to save for revision
                    where: {
                        $and: [
                            {
                                lastchangeAt: {
                                    $or: {
                                        $eq: null,
                                        $and: {
                                            $ne: null,
                                            $gt: sequelize.col('createdAt')
                                        }
                                    }
                                }
                            },
                            {
                                savedAt: {
                                    $or: {
                                        $eq: null,
                                        $lt: sequelize.col('lastchangeAt')
                                    }
                                }
                            }
                        ]
                    }
                }).then(function (notes) {
                    if (notes.length <= 0) return callback(null, notes);
                    var savedNotes = [];
                    async.each(notes, function (note, _callback) {
                        // revision saving policy: note not been modified for 5 mins or not save for 10 mins
                        if (note.lastchangeAt && note.savedAt) {
                            var lastchangeAt = moment(note.lastchangeAt);
                            var savedAt = moment(note.savedAt);
                            if (moment().isAfter(lastchangeAt.add(5, 'minutes'))) {
                                savedNotes.push(note);
                                Revision.saveNoteRevision(note, _callback);
                            } else if (lastchangeAt.isAfter(savedAt.add(10, 'minutes'))) {
                                savedNotes.push(note);
                                Revision.saveNoteRevision(note, _callback);
                            } else {
                                return _callback(null, null);
                            }
                        } else {
                            savedNotes.push(note);
                            Revision.saveNoteRevision(note, _callback);
                        }
                    }, function (err) {
                        if (err) return callback(err, null);
                        // return null when no notes need saving at this moment but have delayed tasks to be done 
                        var result = ((savedNotes.length == 0) && (notes.length > savedNotes.length)) ? null : savedNotes;
                        return callback(null, result);
                    });
                }).catch(function (err) {
                    return callback(err, null);
                });
            },
            saveNoteRevision: function (note, callback) {
                Revision.findAll({
                    where: {
                        noteId: note.id
                    },
                    order: '"createdAt" DESC'
                }).then(function (revisions) {
                    if (revisions.length <= 0) {
                        // if no revision available
                        Revision.create({
                            noteId: note.id,
                            lastContent: note.content,
                            length: LZString.decompressFromBase64(note.content).length,
                            authorship: note.authorship
                        }).then(function (revision) {
                            Revision.finishSaveNoteRevision(note, revision, callback);
                        }).catch(function (err) {
                            return callback(err, null);
                        });
                    } else {
                        var latestRevision = revisions[0];
                        var lastContent = LZString.decompressFromBase64(latestRevision.content || latestRevision.lastContent);
                        var content = LZString.decompressFromBase64(note.content);
                        sendDmpWorker({
                            msg: 'create patch',
                            lastDoc: lastContent,
                            currDoc: content,
                        }, function (err, patch) {
                            if (err) logger.error('save note revision error', err);
                            if (!patch) {
                                // if patch is empty (means no difference) then just update the latest revision updated time 
                                latestRevision.changed('updatedAt', true); 
                                latestRevision.update({
                                    updatedAt: Date.now()
                                }).then(function (revision) {
                                    Revision.finishSaveNoteRevision(note, revision, callback);
                                }).catch(function (err) {
                                    return callback(err, null);
                                });
                            } else {
                                Revision.create({
                                    noteId: note.id,
                                    patch: LZString.compressToBase64(patch),
                                    content: note.content,
                                    length: LZString.decompressFromBase64(note.content).length,
                                    authorship: note.authorship
                                }).then(function (revision) {
                                    // clear last revision content to reduce db size
                                    latestRevision.update({
                                        content: null
                                    }).then(function () {
                                        Revision.finishSaveNoteRevision(note, revision, callback);
                                    }).catch(function (err) {
                                        return callback(err, null);
                                    });
                                }).catch(function (err) {
                                    return callback(err, null);
                                });
                            }
                        });
                    }
                }).catch(function (err) {
                    return callback(err, null);
                });
            },
            finishSaveNoteRevision: function (note, revision, callback) {
                note.update({
                    savedAt: revision.updatedAt
                }).then(function () {
                    return callback(null, revision);
                }).catch(function (err) {
                    return callback(err, null);
                });
            }
        }
    });

    return Revision;
};