uses step

Showcard.after.js

Showcard.prototype.ensureHasUrls = function(cb) {
	
	// If they have urls in the corresponding meta record, 
	// then add them. Otherwise, grab them from google and save
	// the meta object for later. 
	
	// For now, lazily aggregate the urls. Never do this automatically when finding a showcard
	// it needs to be clear when you are joining/proxying data, and callers need control	

	// Ignore google API Abuse errors so it can still finish 
	// if Google limits us. 
	
	// We store them on meta.showcards because we don't want them to get wiped out
	// between imports. 
	
	
	// EXPERIMENT: (sean) I'm experimenting with flow control here, using Step. 
	// it lets you describe what you're doing. With a sort of inline comment
	// It automatically handles if (err) return cb(err), as well as flattens
	// asynchronous stuff so you can lay it out in order. 
	
	// If an error occurs, it will tell you which step you were on. 
	
	// We could add a log that dumps out what step you're on too. 
	
	// Let me know what you think.
	
	var self = this
	var step = new Step(cb)
	
	step('look in meta.showcards for the urls', function(done) {
		meta.findOne({_id: self.showcardId()}, done)
	})
	
	step('if we dont find one then go get it', function(done, info) {
		if (info) return done(null, info.wikipediaUrl, info.imdbUrl, false)
		
		var step = new Step(done)
		
		step('get wikipedia url', function(done, info) {
			google.wikipediaUrl(self.title(), function(err, wikipediaUrl) {
				if (err && !err.message.match(/Abuse/)) return done(err)	
				done(null, wikipediaUrl)
			})
		})

		step('get imdb url', function(done, wikipediaUrl) {
			google.imdbUrl(self.title(), function(err, imdbUrl) {
				if (err && !err.message.match(/Abuse/)) return cb(err)
				done(null, wikipediaUrl, imdbUrl)
			})
		})

		step('cache the urls to meta.showcards', function(done, wikipediaUrl, imdbUrl) {
			if (!wikipediaUrl || !imdbUrl) return done()
			meta.save({_id: self.showcardId(), wikipediaUrl: wikipediaUrl, imdbUrl: imdbUrl}, function(err) {
				done(err, wikipediaUrl, imdbUrl, true)
			})
		})
	})
	
	step('set urls on showcard and finish', function(done, wikipediaUrl, imdbUrl, wasGenerated) {
		self.wikipediaUrl(wikipediaUrl)
		self.imdbUrl(imdbUrl)
		done(null, wasGenerated)
	})

})

Showcard.before.js

Showcard.prototype.ensureHasUrls = function(cb) {
	
	// If they have urls in the corresponding meta record, 
	// then add them. Otherwise, grab them from google and save
	// the meta object for later. 
	
	// For now, lazily aggregate the urls. Never do this automatically when finding a showcard
	// it needs to be clear when you are joining/proxying data, and callers need control	

	// Ignore google API Abuse errors so it can still finish 
	// if Google limits us. 
	
	// We store them on meta.showcards because we don't want them to get wiped out
	// between imports. 
	
	function setUrlsAndFinish(wikipediaUrl, imdbUrl, wasGenerated) {
		self.wikipediaUrl(wikipediaUrl)
		self.imdbUrl(imdbUrl)
		cb(null, wasGenerated)
	}
	
	function saveUrls(wikipediaUrl, imdbUrl, innerCb) {
		if (wikipediaUrl && imdbUrl) {
			meta.save({_id: self.showcardId(), wikipediaUrl: wikipediaUrl, imdbUrl: imdbUrl}, function(err) {
				innerCb(err)
			})
		}
			
		else {
			innerCb()
		}
	}
	
	meta.findOne({_id: self.showcardId()}, function(err, info) {
		if (err) return cb(err)
		if (info) return setUrlsAndFinish(info.wikipediaUrl, info.imdbUrl, false)
	
		google.wikipediaUrl(self.title(), function(err, wikipediaUrl) {
			if (err && !err.message.match(/Abuse/)) return cb(err)	
			google.imdbUrl(self.title(), function(err, imdbUrl) {
				if (err && !err.message.match(/Abuse/)) return cb(err)
				saveUrls(wikipediaUrl, imdbUrl, function(err) {
					if (err) return cb(err)
					setUrlsAndFinish(wikipediaUrl, imdbUrl, true)					
				})
			})
		})
	})
	
}

Step.js

module.exports = function Step(cb) {

	// generates a "step" function, which executes stuff in sequence
	// see testStep. Used for flow control. 
	
	var actions = []
	var action = null
	
	function step(description, work) {
		actions.push({description: description, work: work})
		process.nextTick(function() {
			start()
		})
	}
	
	function start(args) {
		if (action) return
		action = actions.shift()
		args = args || []
		args = [done].concat(args)
		action.work.apply(null, args)
	}
	
	function handleError(err) {
		err.message = "Step '" + action.description + "': " + err.message
		return cb(err)
	}
	
	function done(err) {
		if (err) return handleError(err)
		var args = Array.prototype.slice.call(arguments, 1)		
		if (actions.length == 0) return cb.apply(null, arguments)
		action = null		
		start(args)
	}
	
	return step
}