/**
 * Include mixin for ./model.js
 */
module.exports = Inclusion;

function Inclusion() {
}

/**
 * Allows you to load relations of several objects and optimize numbers of requests.
 *
 * @param {Array} objects - array of instances
 * @param {String}, {Object} or {Array} include - which relations you want to load.
 * @param {Function} cb - Callback called when relations are loaded
 *
 * Examples:
 *
 * - User.include(users, 'posts', function() {}); will load all users posts with only one additional request.
 * - User.include(users, ['posts'], function() {}); // same
 * - User.include(users, ['posts', 'passports'], function() {}); // will load all users posts and passports with two
 *     additional requests.
 * - Passport.include(passports, {owner: 'posts'}, function() {}); // will load all passports owner (users), and all
 *     posts of each owner loaded
 * - Passport.include(passports, {owner: ['posts', 'passports']}); // ...
 * - Passport.include(passports, {owner: [{posts: 'images'}, 'passports']}); // ...
 *
 */
Inclusion.include = function (objects, include, cb) {
    var self = this;

    if (
        (include.constructor.name == 'Array' && include.length == 0) ||
        (include.constructor.name == 'Object' && Object.keys(include).length == 0)
        ) {
        cb(null, objects);
        return;
    }

    include = processIncludeJoin(include);

    var keyVals = {};
    var objsByKeys = {};

    var nbCallbacks = 0;
    for (var i = 0; i < include.length; i++) {
        var callback = processIncludeItem(objects, include[i], keyVals, objsByKeys);
        if (callback !== null) {
            nbCallbacks++;
            callback(function() {
                nbCallbacks--;
                if (nbCallbacks == 0) {
                    cb(null, objects);
                }
            });
        } else {
            cb(null, objects);
        }
    }

    function processIncludeJoin(ij) {
        if (typeof ij === 'string') {
            ij = [ij];
        }
        if (ij.constructor.name === 'Object') {
            var newIj = [];
            for (var key in ij) {
                var obj = {};
                obj[key] = ij[key];
                newIj.push(obj);
            }
            return newIj;
        }
        return ij;
    }

    function processIncludeItem(objs, include, keyVals, objsByKeys) {
        var relations = self.relations;

        if (include.constructor.name === 'Object') {
            var relationName = Object.keys(include)[0];
            var subInclude = include[relationName];
        } else {
            var relationName = include;
            var subInclude = [];
        }
        var relation = relations[relationName];

        if (!relation) {
            return function() {
                cb(new Error('Relation "' + relationName + '" is not defined for ' + self.modelName + ' model'));
            }
        }

        var req = {'where': {}};

        if (!keyVals[relation.keyFrom]) {
            objsByKeys[relation.keyFrom] = {};
            objs.filter(Boolean).forEach(function(obj) {
                if (!objsByKeys[relation.keyFrom][obj[relation.keyFrom]]) {
                    objsByKeys[relation.keyFrom][obj[relation.keyFrom]] = [];
                }
                objsByKeys[relation.keyFrom][obj[relation.keyFrom]].push(obj);
            });
            keyVals[relation.keyFrom] = Object.keys(objsByKeys[relation.keyFrom]);
        }

        if (keyVals[relation.keyFrom].length > 0) {
            // deep clone is necessary since inq seems to change the processed array
            var keysToBeProcessed = {};
            var inValues = [];
            for (var j = 0; j < keyVals[relation.keyFrom].length; j++) {
                keysToBeProcessed[keyVals[relation.keyFrom][j]] = true;
                if (keyVals[relation.keyFrom][j] !== 'null' && keyVals[relation.keyFrom][j] !== 'undefined') {
                    inValues.push(keyVals[relation.keyFrom][j]);
                }
            }

            req['where'][relation.keyTo] = {inq: inValues};
            req['include'] = subInclude;

            return function(cb) {
                relation.modelTo.all(req, function(err, objsIncluded) {
                    for (var i = 0; i < objsIncluded.length; i++) {
                        delete keysToBeProcessed[objsIncluded[i][relation.keyTo]];
                        var objectsFrom = objsByKeys[relation.keyFrom][objsIncluded[i][relation.keyTo]];
                        for (var j = 0; j < objectsFrom.length; j++) {
                            if (!objectsFrom[j].__cachedRelations) {
                                objectsFrom[j].__cachedRelations = {};
                            }
                            if (relation.multiple) {
                                if (!objectsFrom[j].__cachedRelations[relationName]) {
                                    objectsFrom[j].__cachedRelations[relationName] = [];
                                }
                                objectsFrom[j].__cachedRelations[relationName].push(objsIncluded[i]);
                            } else {
                                objectsFrom[j].__cachedRelations[relationName] = objsIncluded[i];
                            }
                        }
                    }

                    // No relation have been found for these keys
                    for (var key in keysToBeProcessed) {
                        var objectsFrom = objsByKeys[relation.keyFrom][key];
                        for (var j = 0; j < objectsFrom.length; j++) {
                            if (!objectsFrom[j].__cachedRelations) {
                                objectsFrom[j].__cachedRelations = {};
                            }
                            objectsFrom[j].__cachedRelations[relationName] = relation.multiple ? [] : null;
                        }
                    }
                    cb(err, objsIncluded);
                });
            };
        }


        return null;
    }
}