Namespaced and "stateful" event emitter.

namespaced-events.coffee

###
# Kris Walker <[email protected]>
# Copyright 2011 Licensed under the MIT License http://opensource.org/licenses/mit-license.php
#
# Namespaced and Stateful events

# * Event names are namespaced
# * Event name specificity is separated by a dot "."
# * Event names get more specific from left to right.
#
# - So when the event named "foo.bar" is emitted handlers attached to "foo" and "foo.bar"
#   will be triggered. But if the "foo" event is emitted, only the handler attached to
#   "foo" will be triggered. If the event "bar" is emitted, neither will be triggered.
#
#  * Also, the emitter is stateful; it remembers the last data fired on each event.
#
# - So, when you attach a handler to the event "foo.bar" after it has already been fired,
#   your handler will be triggered even though it technically missed the event.
#
# Gotcha: These events are not emitted or triggered on another event loop, which
# can wreak havoc on existing architecture. .emit() should default to async and there
# should be another method created called .emitSync() to avoid confusion.
#
# This code depends on jQuery ($) and a locally contrived "require()" system... but you
# can easily replace that code.
#
# And this could probably be optimized too.
###
 
declare (require, exports) ->   
    logging = require 'logging'

    walkPath = (path, callback) ->
        agg = []
        for part in path.split('.')
            agg.push(part)
            callback(agg.join('.'))
        return

    invoke = (fn, data, context) ->
        data = $.isArray(data) and data or (data and [data] or [])
        try
            fn.apply(context or {}, data)
        catch e
            return e
        return

    class Registry
        dict: {}

        bind: (path, fn) ->
            if not $.isArray(@dict[path])
                @dict[path] = []

            @dict[path].push(fn)
            return @

        broadcast: (path, data, context) ->
            callbacks = @dict[path]

            if $.isArray(callbacks)
                for fn in callbacks
                    err = invoke(fn, data, context)
                    if err
                        logging.log("callback error on '#{ path }'")
                        logging.log(err)

    class Emitter
        constructor: ->
            @callbackRegistry = new Registry()
            @eventMemo = {}

        emit: (path, data, context) ->
            context or= @
            walkPath path, (namespace) =>
                @callbackRegistry.broadcast(namespace, data, context)
                @eventMemo[namespace] = {data: data, context: context}

        on: (path, fn) ->
            @callbackRegistry.bind(path, fn)
            history = @eventMemo[path]
            if history
                {data, context} = history
                err = invoke(fn, data, context)
                if err
                    logging.log("callback error on '#{ path }'")
                    logging.log(err)


    exports.Emitter = Emitter
    return