1 files changed, 82 insertions, 0 deletions
diff --git a/lib/epub.js/src/utils/hook.js b/lib/epub.js/src/utils/hook.js
new file mode 100644
index 0000000..ea1b901
--- /dev/null
+++ b/lib/epub.js/src/utils/hook.js
@@ -0,0 +1,82 @@
+/**
+ * Hooks allow for injecting functions that must all complete in order before finishing
+ * They will execute in parallel but all must finish before continuing
+ * Functions may return a promise if they are asycn.
+ * @param {any} context scope of this
+ * @example this.content = new EPUBJS.Hook(this);
+ */
+class Hook {
+	constructor(context){
+		this.context = context || this;
+		this.hooks = [];
+	}
+
+	/**
+	 * Adds a function to be run before a hook completes
+	 * @example this.content.register(function(){...});
+	 */
+	register(){
+		for(var i = 0; i < arguments.length; ++i) {
+			if (typeof arguments[i]  === "function") {
+				this.hooks.push(arguments[i]);
+			} else {
+				// unpack array
+				for(var j = 0; j < arguments[i].length; ++j) {
+					this.hooks.push(arguments[i][j]);
+				}
+			}
+		}
+	}
+
+	/**
+	 * Removes a function
+	 * @example this.content.deregister(function(){...});
+	 */
+	deregister(func){
+		let hook;
+		for (let i = 0; i < this.hooks.length; i++) {
+			hook = this.hooks[i];
+			if (hook === func) {
+				this.hooks.splice(i, 1);
+				break;
+			}
+		}
+	}
+
+	/**
+	 * Triggers a hook to run all functions
+	 * @example this.content.trigger(args).then(function(){...});
+	 */
+	trigger(){
+		var args = arguments;
+		var context = this.context;
+		var promises = [];
+
+		this.hooks.forEach(function(task) {
+			try {
+				var executing = task.apply(context, args);
+			} catch (err) {
+				console.log(err);
+			}
+
+			if(executing && typeof executing["then"] === "function") {
+				// Task is a function that returns a promise
+				promises.push(executing);
+			}
+			// Otherwise Task resolves immediately, continue
+		});
+
+
+		return Promise.all(promises);
+	}
+
+	// Adds a function to be run before a hook completes
+	list(){
+		return this.hooks;
+	}
+
+	clear(){
+		return this.hooks = [];
+	}
+}
+export default Hook;