Provide a way to prevent closing Webamp

Fixes #653

docs/usage.md

@@ -216,6 +216,21 @@ const unsubscribe = webamp.onTrackDidChange((track => {
 unsubscribe();
 ```
 
+### `onWillClose(callback)`
+
+A callback which will be called when Webamp is _about to_ closed. Returns an "unsubscribe" function. The callback will be passed a `cancel` function which you can use to conditionally prevent Webamp from being closed.
+
+```JavaScript
+const unsubscribe = webamp.onClose((cancel) => {
+    if (!window.confirm("Are you sure you want to close Webamp?")) {
+        cancel();
+    }
+});
+
+// If at some point in the future you want to stop listening to these events:
+unsubscribe();
+```
+
 ### `onClose(callback)`
 
 A callback which will be called when Webamp is closed. Returns an "unsubscribe" function.

index.d.ts

@@ -160,6 +160,15 @@ export default class Webamp {
    */
   public onTrackDidChange(callback: (track: Track) => any): () => void;
 
+  /**
+   * A callback which will be called when Webamp is _about to_ closed. Returns an
+   * "unsubscribe" function. The callback will be passed a `cancel` function
+   * which you can use to conditionally prevent Webamp from being closed.
+   *
+   * @returns An "unsubscribe" function. Useful if at some point in the future you want to stop listening to these events.
+   */
+  public onWillClose(callback: (cancel: () => void) => any): () => void;
+
   /**
    * A callback which will be called when Webamp is closed.
    *

js/actionCreators/index.ts

@@ -1,4 +1,9 @@
-import { CLOSE_WINAMP, STOP, TOGGLE_VISUALIZER_STYLE } from "../actionTypes";
+import {
+  CLOSE_WINAMP,
+  STOP,
+  TOGGLE_VISUALIZER_STYLE,
+  CLOSE_REQUESTED
+} from "../actionTypes";
 import { Dispatchable } from "../types";
 
 export {
@@ -71,8 +76,17 @@ export {
 
 export function close(): Dispatchable {
   return dispatch => {
-    dispatch({ type: STOP });
-    dispatch({ type: CLOSE_WINAMP });
+    // TODO: This could probably be improved by adding a "PREVENT_CLOSE" action
+    // or something, but this works okay for now.
+    let defaultPrevented = false;
+    const cancel = () => {
+      defaultPrevented = true;
+    };
+    dispatch({ type: CLOSE_REQUESTED, cancel });
+    if (!defaultPrevented) {
+      dispatch({ type: STOP });
+      dispatch({ type: CLOSE_WINAMP });
+    }
   };
 }
 

js/actionTypes.ts

@@ -70,3 +70,4 @@ export const DISABLE_MARQUEE = "DISABLE_MARQUEE";
 export const SET_DUMMY_VIZ_DATA = "SET_DUMMY_VIZ_DATA";
 export const SET_WINDOW_VISIBILITY = "SET_WINDOW_VISIBILITY";
 export const LOADING = "LOADING";
+export const CLOSE_REQUESTED = "CLOSE_REQUESTED";

js/index.js

@@ -262,6 +262,12 @@ Raven.context(() => {
     });
   }
 
+  webamp.onWillClose(cancel => {
+    if (!window.confirm("Are you sure you want to close Webamp?")) {
+      cancel();
+    }
+  });
+
   webamp.renderWhenReady(document.getElementById("app"));
 
   // Expose webamp instance for debugging and integration tests.

js/types.ts

@@ -327,6 +327,10 @@ export type Action =
     }
   | {
       type: "MINIMIZE_WINAMP";
+    }
+  | {
+      type: "CLOSE_REQUESTED";
+      cancel: () => void;
     };
 
 export interface SettingsState {

js/webampLazy.js

@@ -27,7 +27,8 @@ import {
   LOADED,
   REGISTER_VISUALIZER,
   SET_Z_INDEX,
-  SET_MEDIA
+  SET_MEDIA,
+  CLOSE_REQUESTED
 } from "./actionTypes";
 import Emitter from "./emitter";
 
@@ -182,6 +183,12 @@ class Winamp {
     this.store.dispatch(loadMediaFiles(tracks, LOAD_STYLE.PLAY));
   }
 
+  onWillClose(cb) {
+    return this._actionEmitter.on(CLOSE_REQUESTED, action => {
+      cb(action.cancel);
+    });
+  }
+
   onClose(cb) {
     return this._actionEmitter.on(CLOSE_WINAMP, cb);
   }