Add opening images in a modal window

app/assets/javascripts/components/reducers/modal.jsx

@@ -0,0 +1,21 @@
+import { MEDIA_OPEN, MODAL_CLOSE } from '../actions/modal';
+import Immutable                   from 'immutable';
+
+const initialState = Immutable.Map({
+  url: '',
+  open: false
+});
+
+export default function modal(state = initialState, action) {
+  switch(action.type) {
+    case MEDIA_OPEN:
+      return state.withMutations(map => {
+        map.set('url', action.url);
+        map.set('open', true);
+      });
+    case MODAL_CLOSE:
+      return state.set('open', false);
+    default:
+      return state;
+  }
+};