// Main function to initialise plemp
function init_plemp(base_url) {
  setup_pu();
  document.onkeyup=key_handler;
}

// Creates a Draggable for each div with the given ID.
function setup_draggables() {
  $$('.draggable').each(function(d) { setup_draggable(d.id); });
}

function setup_draggable(id) {
  drag = new Draggable(id, { scroll: window });
  old_endeffect = drag.options.endeffect;
  drag.options.endeffect = function(element) { 
    old_endeffect(element); 
    element.style.zIndex = new_ZIndex();
  }
  drag_obs = new DragRegObserver($(id));
  Draggables.addObserver(drag_obs);
  $(id).dirty = false;
  $(id).appear();
}

// Observer for draggables that commits the drag changes to the server.
var DragRegObserver = Class.create();
DragRegObserver.prototype = {
  initialize: function(element) {
    this.element = $(element);
  },
  onStart: function(eventName, draggable, event) {
    draggable.element.dirty = true;
  },
  onEnd: function (eventName, draggable, event) {
    if (Draggables.activeDraggable.element == this.element) {
      elem = draggable.element;
      new Ajax.Request(document.baseURI + 'savepos/' + elem.id + 
                       '/' + elem.style.top + '/' + elem.style.left, {
        onSuccess: function(response) { elem.dirty = false; }
      });
    }
  }
}

// Global function to handle key presses.
function key_handler(e) {
  var key_code = e.keyCode;

  switch(key_code) {
    case 27: /* Escape */
      hide_add_dialog();
      break;
    case 187: /* Plus */
      show_add_dialog();
      break;
  }
}

//// Helper functions

// Shows the upload/add dialog.
function show_add_dialog() {
  if (!$('add_dialog').visible()) {
    $('text').clear();
    $('add_dialog').appear({duration: 0.25});
  }
}

// Hides and clears the upload/add dialog.
function hide_add_dialog() {
  if ($('add_dialog').visible()) {
    $('add_dialog').fade({duration: 0.25});
    $('add_form').reset();
  }
}

// Returns a Z-index higher with respect to the Z-index of all existing
// draggables.
function new_ZIndex() {
  cur_indices = $$('.draggable').map(function(d) { return d.getStyle("z-index") })
  max_index = cur_indices.max();
  return parseInt(max_index) + 1;
}

// Moves a draggable with the given ID to a position unless:
// it is currently being dragged, or it has been dragged but not this is
// not registered at the server side yet, or it is already on the right spot.
function move_draggable_if_needed(id, left, top) {
  var actDrag = Draggables.activeDraggable;
  if ($(id).dirty || (actDrag && actDrag.element == $(id))) { 
    return false;
  }
  if ($(id).style.left != left || $(id).style.top != top) {
    new Effect.Move(id, { x: left, y: top, mode: 'absolute' });
  }
}

// Sets up an Ajax periodical updater to retrieve the current global
// state from the server.  Moves the draggables accordingly.
var pu = null;
function setup_pu() {
  if (!pu) {
    pu = new Ajax.PeriodicalUpdater('', document.baseURI + "current/", {
           method: 'get',
           frequency: 5,
           evalJSON: 'force',
           onSuccess: function(t) { 
             var json = t.responseJSON;
             if (json) {
               $H(json).each(function(pair) {
                 move_draggable_if_needed(pair.key, pair.value[0],
                                                    pair.value[1]);
               });
             }
           },
           onFailure: function() { alert("Something went wrong!") }
         });
  }
}