/** @module cacheManager/caching */
/*jshint maxcomplexity:15*/
var domain = require('domain');
var CallbackFiller = require('./callback_filler');

/**
 * Generic caching interface that wraps any caching library with a compatible interface.
 *
 * @param {object} args
 * @param {object|string} args.store - The store must at least have `set` and a `get` functions.
 * @param {function} [args.isCacheableValue] - A callback function which is called
 *   with every value returned from cache or from a wrapped function. This lets you specify
 *   which values should and should not be cached. If the function returns true, it will be
 *   stored in cache. By default it caches everything except undefined.
 */
var caching = function(args) {
    args = args || {};
    var self = {};
    if (typeof args.store === 'object') {
        if (args.store.create) {
            self.store = args.store.create(args);
        } else {
            self.store = args.store;
        }
    } else {
        var storeName = args.store || 'memory';
        self.store = require('./stores/' + storeName).create(args);
    }

    // do we handle a cache error the same as a cache miss?
    self.ignoreCacheErrors = args.ignoreCacheErrors || false;

    var callbackFiller = new CallbackFiller();

    if (typeof args.isCacheableValue === 'function') {
        self._isCacheableValue = args.isCacheableValue;
    } else if (typeof self.store.isCacheableValue === 'function') {
        self._isCacheableValue = self.store.isCacheableValue;
    } else {
        self._isCacheableValue = function(value) {
            return value !== undefined;
        };
    }

    /**
     * Wraps a function in cache. I.e., the first time the function is run,
     * its results are stored in cache so subsequent calls retrieve from cache
     * instead of calling the function.
     *
     * @function
     * @name wrap
     *
     * @param {string} key - The cache key to use in cache operations
     * @param {function} work - The function to wrap
     * @param {object} [options] - options passed to `set` function
     * @param {function} cb
     *
     * @example
     *   var key = 'user_' + userId;
     *   cache.wrap(key, function(cb) {
     *       User.get(userId, cb);
     *   }, function(err, user) {
     *       console.log(user);
     *   });
     */
    self.wrap = function(key, work, options, cb) {
        if (typeof options === 'function') {
            cb = options;
            options = {};
        }

        if (!cb) {
            cb = Promise.defer();
            var work2 = work;
            work = function(cb) {
                Promise.resolve().then(work2).then(function(res) {
                    cb(null, res);
                })
                .catch(cb);
            };
        }

        var hasKey = callbackFiller.has(key);
        callbackFiller.add(key, {cb: cb, domain: process.domain});
        if (hasKey) { return; }

        self.store.get(key, options, function(err, result) {
            if (err && (!self.ignoreCacheErrors)) {
                callbackFiller.fill(key, err);
            } else if (self._isCacheableValue(result)) {
                callbackFiller.fill(key, null, result);
            } else {
                domain
                .create()
                .on('error', function(err) {
                    callbackFiller.fill(key, err);
                })
                .bind(work)(function(err, data) {
                    if (err) {
                        callbackFiller.fill(key, err);
                        return;
                    }

                    if (!self._isCacheableValue(data)) {
                        if (typeof cb === 'object') {
                            return cb.resolve(data);
                        }
                        return cb();
                    }

                    self.store.set(key, data, options, function(err) {
                        if (err && (!self.ignoreCacheErrors)) {
                            callbackFiller.fill(key, err);
                        } else {
                            callbackFiller.fill(key, null, data);
                        }
                    });
                });
            }
        });

        if (typeof cb === 'object') {
            return cb.promise;
        }
    };

    /**
     * Binds to the underlying store's `get` function.
     * @function
     * @name get
     */
    self.get = self.store.get.bind(self.store);

    /**
     * Binds to the underlying store's `set` function.
     * @function
     * @name set
     */
    self.set = self.store.set.bind(self.store);

    /**
     * Binds to the underlying store's `del` function if it exists.
     * @function
     * @name del
     */
    if (typeof self.store.del === 'function') {
        self.del = self.store.del.bind(self.store);
    }

    /**
     * Binds to the underlying store's `setex` function if it exists.
     * @function
     * @name setex
     */
    if (typeof self.store.setex === 'function') {
        self.setex = self.store.setex.bind(self.store);
    }

    /**
     * Binds to the underlying store's `reset` function if it exists.
     * @function
     * @name reset
     */
    if (typeof self.store.reset === 'function') {
        self.reset = self.store.reset.bind(self.store);
    }

    /**
     * Binds to the underlying store's `keys` function if it exists.
     * @function
     * @name keys
     */
    if (typeof self.store.keys === 'function') {
        self.keys = self.store.keys.bind(self.store);
    }

    /**
     * Binds to the underlying store's `ttl` function if it exists.
     * @function
     * @name ttl
     */
    if (typeof self.store.ttl === 'function') {
        self.ttl = self.store.ttl.bind(self.store);
    }

    return self;
};

module.exports = caching;