feat(modeling): add feedback on invalid modeling action

This commit adds the ModelingFeedback component. It hooks into
modeling action rejected events and displays error messages
to the user.

The current behavior is to show an error message when dropping
a flow node outside a participant in a collaboration.

Related to #203

lib/features/modeling/behavior/ModelingFeedback.js

@@ -0,0 +1,36 @@
+'use strict';
+
+var is = require('../../../util/ModelUtil').is;
+
+
+function ModelingFeedback(eventBus, tooltips) {
+
+  function showError(position, message) {
+    tooltips.add({
+      position: {
+        x: position.x + 5,
+        y: position.y + 5
+      },
+      type: 'error',
+      timeout: 2000,
+      html: '<div>' + message + '</div>'
+    });
+  }
+
+  eventBus.on([ 'shape.move.rejected', 'create.rejected' ], function(event) {
+
+    var context = event.context,
+        shape = context.shape,
+        target = context.target;
+
+    if (is(target, 'bpmn:Collaboration') && is(shape, 'bpmn:FlowNode')) {
+      showError(event, 'flow elements must be children of pools/participants');
+    }
+  });
+
+}
+
+
+ModelingFeedback.$inject = [ 'eventBus', 'tooltips' ];
+
+module.exports = ModelingFeedback;

lib/features/modeling/behavior/index.js

@@ -1,7 +1,14 @@
 module.exports = {
-  __init__: [ 'appendBehavior', 'dropBehavior', 'createBehavior', 'removeBehavior' ],
+  __init__: [
+    'appendBehavior',
+    'createBehavior',
+    'dropBehavior',
+    'removeBehavior',
+    'modelingFeedback'
+  ],
   appendBehavior: [ 'type', require('./AppendBehavior') ],
+  dropBehavior: [ 'type', require('./DropBehavior') ],
   createBehavior: [ 'type', require('./CreateBehavior') ],
   removeBehavior: [ 'type', require('./RemoveBehavior') ],
-  dropBehavior: [ 'type', require('./DropBehavior') ]
+  modelingFeedback: [ 'type', require('./ModelingFeedback') ]
 };

lib/features/modeling/index.js

@@ -5,6 +5,7 @@ module.exports = {
     require('./rules'),
     require('./behavior'),
     require('diagram-js/lib/command'),
+    require('diagram-js/lib/features/tooltips'),
     require('diagram-js/lib/features/change-support')
   ],
   bpmnFactory: [ 'type', require('./BpmnFactory') ],