SJS Channel vs Emitter 01

@ = require(['mho:std', 'mho:app']);


// channel.sjs
;(function (exports) {
  exports.pending_limit = 1024

  exports.closed = {}


  function wake(array, value) {
    var f = array.shift()
    return f(value)
  }

  function sleep(chan_this, value) {
    if (chan_this.length < exports.pending_limit) {
      // TODO why doesn't this hold work ?
      // hold(0)
      waitfor (var result) {
        function done(x) {
          // TODO is this a good spot for this ?
          // TODO is there a better way than using hold(0) ?
          hold(0)
          resume(x)
          return value
        }
        chan_this.push(done)
      } retract {
        var index = chan_this.indexOf(done)
        console.log("RETRACTED", index)
        @assert.isNot(index, -1) // TODO test if this is ever possible
        if (index !== -1) {
          chan_this.splice(index, 1)
        }
      }
      return result
    } else {
      throw new Error("cannot have more than #{exports.pending_limit} pending operations on a channel")
    }
  }


  // The behavior is the same as Clojure's core.async channels (http://clojure.github.io/core.async/)
  exports.Channel = function () {
    // TODO what about pending receiver/sender when retracted ?
    var o = @Stream(function (emit) {
      while (true) {
        // TODO I would like to use `exports.take(this)`, but I can't
        var v = exports.take(o)
        if (v === exports.closed) {
          break
        } else {
          emit(v)
        }
      }
    })

    o.closed   = false
    o.receiver = []
    o.sender   = []

    return o
  }

  exports.take = function (channel) {
    if (channel.sender.length) {
      return wake(channel.sender, null)
    } else if (channel.closed) {
      return exports.closed
    } else {
      return sleep(channel.receiver, null)
    }
  }

  // TODO this used to return something even though it didn't use return! find out why
  exports.put = function (channel, value) {
    if (channel.closed) {
      return false
    } else if (channel.receiver.length) {
      wake(channel.receiver, value)
      return true
    } else {
      sleep(channel.sender, value)
      return true
    }
  }

  exports.close = function (channel) {
    channel.closed = true

    while (channel.receiver.length) {
      wake(channel.receiver, exports.closed)
    }
  }

  exports.isClosed = function (channel) {
    return channel.closed
  }
})(@)


// event.sjs
;(function (exports) {
  exports.Emitter = function () {
    var o = @Stream(function (emit) {
      // TODO I would like to use `this` rather than `o`
      var c = exports.on(o)
      try {
        c ..@each(emit)
      } finally {
        exports.off(o, c)
      }
    })

    o.listeners = []

    return o
  }

  exports.on = function (emitter) {
    var c = @Channel()
    emitter.listeners.push(c)
    return c
  }

  exports.off = function (emitter, c) {
    emitter.listeners ..@remove(c)
  }

  exports.emit = function (emitter, value) {
    // TODO use each.par instead ?
    emitter.listeners ..@each(function (listener) {
      listener ..@put(value)
    })
  }
})(@)


// dom.sjs
;(function (exports) {
  exports.events = function (elem, name, info) {
    var o = @Emitter()
    elem.addEventListener(name, function (e) {
      if (info != null) {
        if (info.preventDefault) {
          e.preventDefault()
        }
      }
      o ..@emit(e)
    }, true)
    return o
  }
})(@)


function getUpdateFromServer() {
  hold(1000); // simulate server round trip
  return @Div('This is an update from the server');
}

@mainContent .. @appendContent(@Btn('default', 'Get status update from server')) {
  |button|

  button .. @events('click') ..@buffer(1, { drop: true }) .. @each {
    ||
    waitfor {
      @mainContent .. @appendContent(getUpdateFromServer());
    }
    or {
      hold(100); // wait a little while before showing feedback

      // actually want to append to status bar here or something, but this is for demo only
      @mainContent .. @appendContent('waiting for server...') { || hold() }
    }
  }
}