epub.js/fpjs/render/storage_indexeddb.js

FP.store = FP.store || {};

FP.store.indexedDB = function() {
	var _store = {},
		_blobs = {},
		_queue = new FP.Queue(loader, 6),
		_indexedDB = window.indexedDB || window.mozIndexedDB || window.webkitIndexedDB || window.msIndexedDB,
		_db;

	const DBNAME = "fpjs_db";

	//-- max of 6 concurrent requests: http://www.browserscope.org/?category=network
	function loader(msg, postMessage){
		var e = {"data":null},
			path = msg;

		request(msg, function(file){
				save(path, file);
				postMessage(e);
		});

	}

	function opendb(callback){
		var request;

		if(_db){
			callback(_db);
			return;
		}

		request = indexedDB.open(DBNAME);


		request.onsuccess = function(event) {
		  _db = request.result;

		  _db.onerror = function(event) {
			console.log("Database error: " + event.target.errorCode);
		  };


		  if(callback) callback(_db);

		};


		request.onerror = function(event) {
		  // Handle errors.
		};


		request.onupgradeneeded = function(event) {		
		  var db = event.target.result,
		  	  objectStore = db.createObjectStore("files", { keyPath: "path" }); //keyPath: "id", autoIncrement: true 

		  //objectStore.createIndex("path", "path", { unique: true });

		  //objectStore.createIndex("file", "file", { unique: false });

		};



	}

	function preload(path) {
		// var fromCache = check(path);
		// 
		// if(!fromCache){
		// 	_queue.add(path);
		// }
	}

	function batch(group, callback){
		_queue.addGroup(group, callback);
	}

	//-- Fetches url
	function get(path, callback) {

		if(typeof(_blobs[path]) != "undefined"){
			callback(_blobs[path]);
			return; 
		}

		check(path, function(fromCache){

			var url;

			if(fromCache){
				url = getURL(path, fromCache);
				if(typeof(callback) != "undefined"){
					callback(url);
				}
			}else{
				_queue.add(path, function(file){
					url = getURL(path, file);
					if(typeof(callback) != "undefined"){
						callback(url);
					}
				}, true);
			}

		});


	}

	function check(path, callback) {
		var request,
			objectStore;

		opendb(function(db){
			objectStore = db.transaction(["files"]).objectStore("files");
			request = objectStore.get(path);

			request.onerror = function(event) {
			  callback(false);
			};

			request.onsuccess = function(event) {
			  callback(request.result.file);
			};
		});

	}

	//-- should be in worker

	function request(path, callback) {
		var xhr = new FP.core.loadFile(path);

		xhr.succeeded = function(file) {
			if(typeof(callback) != "undefined"){
				callback(file);
			}
		}

		xhr.failed = _error;

		xhr.start();
	}

	function save(path, file) {
		var	entry = {"path" : path, "file": file},
			request;

		opendb(function(db){
			var transaction = db.transaction(["files"], "readwrite");
			var store = transaction.objectStore("files");	
			request = store.put(entry);

			request.onerror = function(event) {
			  console.log("failed: " + event.target.errorCode);
			};

			request.onsuccess = function(event) {
			  //-- Do nothing for now
			  console.log("saved", path);
			};
		});
	}

	//-- end worker

	function getURL(path, file){
		var url;

		if(typeof(_blobs[path]) != "undefined"){
			callback(_blobs[path]);
			return; 
		}

		url = this._URL.createObjectURL(file);

		//-- need to revokeObjectURL previous urls, but only when cleaning cache
		// this.createdURLs.forEach(function(url){
		// 	this._URL.revokeObjectURL(url);
		// });

		_blobs[path] = url;

		return url;
	}

	function _error(err){
		if(typeof(this.failed) == "undefined"){
			console.log("Error: ", err);
		}else{
			this.failed(err);
		}
	}



	return {
		"get" : get,
		"preload" : preload,
		"batch" : batch
	}	
}