'use strict';

/**
 * Handles generic caching of JSON objects in a lawnchair adapter
 */
app.dao.LawnchairDAO = function(window) {
	
	/**
	 * Create or update an object
	 */
	this.persist = function(key, object, callback) {
		Lawnchair(function() {
			this.save({ key:key, object:object }, callback);
		});
	};
	
	/**
	 * Persist a bunch of items at once
	 */
	this.batch = function(list, callback) {
		Lawnchair(function() {
			this.batch(list, callback);
		});
	};
	
	/**
	 * Read a single item by its key
	 */
	this.read = function(key, callback) {
		Lawnchair(function() {
			this.get(key, function(o) {
				if (o) {
					callback(o.object);
				} else {
					callback(null);
				}
			});
		});
	};
	
	/**
	 * List all the items of a certain type
	 * @param type [String] The type of item e.g. 'email'
	 * @param offset [Number] The offset of items to fetch (0 is the last stored item)
	 * @param num [Number] The number of items to fetch (null means fetch all)
	 */
	this.list = function(type, offset, num, callback) {	
		var i, list = [], matchingKeys = [], parts, timeStr, time;
		
		Lawnchair(function() {
			var self = this;
			
			// get all keys
			this.keys(function(keys) {
				
				// check if key begins with type
				for (i = 0; i < keys.length; i++) {
					if (keys[i].indexOf(type) === 0) {
						matchingKeys.push(keys[i]);
					}
				}					
				
				// sort keys by type and date								
				matchingKeys = _.sortBy(matchingKeys, function(key) {
					parts = key.split('_');
					timeStr = parts[parts.length-2];
					time = parseInt(timeStr, 10);
					return time;
				});			
				
				// if num is null, list all items
				num = (num !== null) ? num : matchingKeys.length;

				// set window of items to fetch
				if (offset + num < matchingKeys.length) {
					matchingKeys = matchingKeys.splice(matchingKeys.length - offset - num, num);
				} else if (offset + num >= matchingKeys.length && offset < matchingKeys.length) {
					matchingKeys = matchingKeys.splice(0, matchingKeys.length - offset);
				} else {
					matchingKeys = [];
				}							
				
				// return if there are no matching keys
				if (matchingKeys.length === 0) {
					callback(list);
					return;
				}
				
				// fetch all items from data-store with matching key
				self.get(matchingKeys, function(matchingList) {
					for (i = 0; i < matchingList.length; i++) {
						list.push(matchingList[i].object);
					}					
					
					// return only the interval between offset and num
					callback(list);
				});			
					
			});
		});
	};
	
	/**
	 * Removes an object liter from local storage by its key (delete)
	 */
	this.remove = function(key, callback) {
		Lawnchair(function() {
			this.remove(key, callback);
		});
	};
	
	/**
	 * Clears the whole local storage cache
	 */
	this.clear = function(callback) {
		Lawnchair(function() {
			this.nuke(callback);
		});
	};
	
};