Glenlivet

Glenlivet is a hook and plugin system that allows you to create flexible, reusable processing workflows.

Installation

npm install glenlivet

Overview

Glenlivet's job is to make it as easy as possible to write and implement plugins. Similar to Grunt, but for writing apps.

• Configure processing workflows declaratively with "bottles"
• Bundle bottles together using "barrels"
• Plugins automatically load based on configuration keys
• Use hooks to attach processing steps to bottles
• Add your own hooks to control processing flow
• Plugins are simple to create, and can be applied to barrels or bottles

Philosophy

Glenlivet is meant to be modular and flexible. Its goal is to allow a bunch of plugins to work together in a loosely coupled way.

How It's Used

So far, it's been used to create the mobile API for the Threadless iPhone App that is mostly backed by scraped data from their website. Plugins are used to layer in user sessions, caching, and HTML to JSON payload mapping.

Barrels and Bottles

Barrels create a logical grouping of bottles. Their purpose is to provide a way to create functionality on top of bottles. For example, you might want to create a web service that interfaces with a group of bottles.

Basic Usage

var glenlivet = require('glenlivet');

var myBarrel = glenlivet.createBarrel({});

var testBottle = myBarrel.createBottle('test', {
	fetch: { //Loads fetch plugin
		uri: 'http://www.prolificinteractive.com:page'
	}
});

testBottle.fetch({
	fetch: {
		page: '/about'
	}
}, function (result) {
	console.log(result.fetch.error || result.fetch.body);
});

Plugins

Plugins typically attach processing steps via bottle hooks. They're loaded using they configuration keys on barrels and bottles.

Creating a Plugin

Plugins are defined with named functions:

function myPlugin (context) {
	context.is(glenlivet.Bottle, function (bottle, myConfig) {
		console.log('I am in a bottle');
	});

	context.is(glenlivet.Barrel, function (bottle, myConfig) {
		console.log('I am in a barrel');
	});
}

Note: Plugins must be defined as named functions:

function correctWay () {}
var incorrectWay = function () {}
var thisWorksToo = function thisWorksToo () {}

Plugin Contexts

Plugins are passed a context object when they're called, which has several methods:

context.is(constructor|constructors, callback)

A single constructor or an array of constructors can be passed in as the first argument.

Tests if the plugin is currently called against an instance of the constructor, and runs the callback with two arguments:

• instance: An object the plugin is running against.
• pluginConfig: The config corresponding to the plugin.

context.using(pluginName, callback)

As a convenience, tests if another plugin is defined in the current context, and runs the callback if so with one argument:

• otherPluginConfig: The config corresponding to the other plugin.

Registering a Plugin

You can register a plugin at multiple scopes: glenlivet, barrels, and bottles.

glenlivet.plugins.register(myPlugin); //At the glenlivet scope
barrel.plugins.register(myPlugin); //At the barrel scope
bottle.plugins.register(myPlugin); //At the bottle scope

Using Hooks

Hooks allow plugins to get along with each other by inserting themselves at different parts of the processing workflow. In Glenlivet, hooks are defined as hierarchies, often by plugins.

Adding and Implementing Hooks

Hooks are added using bottle.hooks.add(hierarchy), and implemented with three methods:

• bottle.hooks.before(colonSeparatedPath, callback)
• bottle.hooks.when(colonSeparatedPath, callback)
• bottle.hooks.after(colonSeparatedPath, callback)

The callback receives:

• result: The object that gets decorated by plugins to yield a result
• next: Used with asynchronous processes. Tells Glenlivet to advance to the next step.
• done: Completes this step and prevents the processing of any further hooks.

If the callback includes only one argument in its signature, it will be run synchronously.

Example

function myPlugin (context) {
	context.is(glenlivet.Bottle, function (bottle, myConfig) {
		bottle.hooks.add({
			myPlugin: {
				setup: {}
			}
		});

		//Synchronous
		bottle.hooks.after('myPlugin:setup', function (result) {
			result.myPlugin.helloWorld = 'hello'
		});

		//Asynchronous
		bottle.hooks.when('myPlugin', function (result, next) {
			setTimeout(function () {
				result.myPlugin.helloWorld += 'world'
				next();
			}, 10);
		});

		//Using the done function
		bottle.hooks.before('myPlugin', function (result, next, done) {
			if (result.foo === 'bar') {
				done();
			}
		});
	});
}

Triggering Hooks

To trigger the hook cascade, use the .trigger() method.

Example

bottle.hooks.trigger('hook:subhook:etc', { foo: 'bar' }, callback);

.trigger() takes 3 arguments:

• hook: the path to the hook
• decorator (optional): an object passed through each hook and finally to the callback
• callback (optional): run after all hooks are triggered

Shortcut Methods

Glenlivet also adds convenience methods to bottles that trigger top-level hooks, like so:

function addition (context) {
	context.is(glenlivet.Bottle, function (bottle, myConfig) {
		bottle.hooks.add({
			addition: {}
		});

		bottle.hooks.when('addition', function (result) {
			result.addition.sum = result.addition.a + result.addition.b;
		});
	});
}

bottle.addition({
	addition: {
		a: 100,
		b: 50
	}
}, function (result) {
	console.log(result.addPlugin.sum); //Should output "150"
});

Joining Hooks

Hooks can be joined together using the .join() method. As a convenience, it can also map decorator values so that, for example, data from one plugin can be seamlessly piped into another.

Example

bottle.plugins.join('hookA', 'hookB', {
	'hookA:x': 'hookB:y'
});

.join() takes 3 arguments

• hookA: the path to the connecting hook
• hookB: the path to the hook that will be triggered after hookA
• map (optional): maps values from one part of the decorator object to another, and creates any part of the path that does not exist