document NewPlayerViewModel interface

new-player/src/main/java/net/newpipe/newplayer/uiModel/NewPlayerViewModel.kt

@@ -5,17 +5,65 @@ import androidx.media3.common.util.UnstableApi
 import kotlinx.coroutines.flow.SharedFlow
 import kotlinx.coroutines.flow.StateFlow
 import net.newpipe.newplayer.NewPlayer
+import net.newpipe.newplayer.ui.NewPlayerUI
 import net.newpipe.newplayer.ui.ContentScale
+import net.newpipe.newplayer.data.PlayMode.IDLE
 
+
+/**
+ * The NewPlayerViewModel must live and be owned by an Activity context.
+ */
 @OptIn(UnstableApi::class)
 interface NewPlayerViewModel {
+
+    /**
+     * The current instance of [NewPlayer]. If set to null the [NewPlayerUI] instance
+     * which the viewModel talks too will display the same as if [NewPlayer] was in [IDLE] mode.
+     *
+     * You can always add or remove the NewPlayer instance.
+     */
     var newPlayer: NewPlayer?
+
+    /**
+     * Depicts weather the picture of the video should be stretched, fit inside or be cropped.
+     * You can set it yourself, but [NewPlayerUI] can also change it.
+     */
     var contentFitMode: ContentScale
 
+    /**
+     * This represents the state the UI is in. [NewPlayerUI] will basically render out that state.
+     * You can make your UI also listen to changes to this state. This is especially helpful
+     * for switching to or from fullscreen or to or from PiP mode.
+     */
     val uiState: StateFlow<NewPlayerUIState>
 
+    /**
+     * If the user dragged down the embedded video or audio player. This callback will tell you
+     * how far the user dragged down. Keep in mind that the user can also decide to drag the
+     * [NewPlayerUI] up again. If the [NewPlayerUI] is not dragged up to its original position
+     * you should take over control and maybe make the [NewPlayerUI] snap to the bottom of the
+     * screen to make space for your UI.
+     */
     val embeddedPlayerDraggedDownBy: SharedFlow<Float>
+
+    /**
+     * [NewPlayerUI] will use some back press events for its own navigation purposes.
+     * If the viewModel decides that a back press event should not be handled by itself.
+     * It will forward the event to you through this callback.
+     */
     val onBackPressed: SharedFlow<Unit>
 
+    /**
+     * This is something you have to call in the Activity that should host the [NewPlayerUI].
+     * See the [example app's](https://github.com/TeamNewPipe/NewPlayer/blob/master/test-app/src/main/java/net/newpipe/newplayer/testapp/MainActivity.kt) main activity to find out how to use this.
+     *
+     * Long story short your activity should handle the `onPictureInPictureModeChanged` event.
+     * You can do this by adding this code to your Activity's `onCreate()` function:
+     * ```
+     *  addOnPictureInPictureModeChangedListener { mode ->
+     *      newPlayerViewModel.onPictureInPictureModeChanged(mode.isInPictureInPictureMode)
+     *  }
+     * ```
+     */
     fun onPictureInPictureModeChanged(isPictureInPictureMode: Boolean)
 }