Prefetch YouTube video info on hover

Speed up loading of YouTube videos by downloading and parsing their info before video is dropped into player.

src/player.js

@@ -26,6 +26,7 @@ class ClapperPlayer extends PlayerBase
         this.needsTocUpdate = true;
 
         this.keyPressCount = 0;
+        this.ytClient = null;
 
         const keyController = new Gtk.EventControllerKey();
         keyController.connect('key-pressed', this._onWidgetKeyPressed.bind(this));
@@ -78,8 +79,10 @@ class ClapperPlayer extends PlayerBase
 
     async getYouTubeUriAsync(videoId)
     {
-        const client = new YouTube.YouTubeClient();
-        const info = await client.getVideoInfoPromise(videoId).catch(debug);
+        if(!this.ytClient)
+            this.ytClient = new YouTube.YouTubeClient();
+
+        const info = await this.ytClient.getVideoInfoPromise(videoId).catch(debug);
 
         if(!info)
             throw new Error('no YouTube video info');
@@ -87,7 +90,7 @@ class ClapperPlayer extends PlayerBase
         const dash = Dash.generateDash(info);
         const videoUri = (dash)
             ? await Dash.saveDashPromise(dash).catch(debug)
-            : client.getBestCombinedUri(info);
+            : this.ytClient.getBestCombinedUri(info);
 
         if(!videoUri)
             throw new Error('no YouTube video URI');

src/widget.js

@@ -4,6 +4,7 @@ const Debug = imports.src.debug;
 const Dialogs = imports.src.dialogs;
 const Misc = imports.src.misc;
 const { Player } = imports.src.player;
+const YouTube = imports.src.youtube;
 const Revealers = imports.src.revealers;
 
 const { debug } = Debug;
@@ -721,9 +722,11 @@ class ClapperWidget extends Gtk.Grid
     {
         const dropTarget = new Gtk.DropTarget({
             actions: Gdk.DragAction.COPY,
+            preload: true,
         });
         dropTarget.set_gtypes([GObject.TYPE_STRING]);
         dropTarget.connect('drop', this._onDataDrop.bind(this));
+        dropTarget.connect('notify::value', this._onDropValueNotify.bind(this));
 
         return dropTarget;
     }
@@ -897,6 +900,31 @@ class ClapperWidget extends Gtk.Grid
         this.posY = posY;
     }
 
+    _onDropValueNotify(dropTarget)
+    {
+        if(!dropTarget.value)
+            return;
+
+        const uris = dropTarget.value.split(/\r?\n/);
+        const firstUri = uris[0];
+
+        if(uris.length > 1 || !Gst.uri_is_valid(firstUri))
+            return;
+
+        /* Check if user is dragging a YouTube link */
+        const [isYouTubeUri, videoId] = YouTube.checkYouTubeUri(firstUri);
+        if(!isYouTubeUri) return;
+
+        /* Since this is a YouTube video,
+         * create YT client if it was not created yet */
+        if(!this.player.ytClient)
+            this.player.ytClient = new YouTube.YouTubeClient();
+
+        /* Speed up things by prefetching new video info before drop */
+        if(!this.player.ytClient.compareLastVideoId(videoId))
+            this.player.ytClient.getVideoInfoPromise(videoId).catch(debug);
+    }
+
     _onDataDrop(dropTarget, value, x, y)
     {
         const playlist = value.split(/\r?\n/).filter(uri => {

src/youtube.js

@@ -4,27 +4,54 @@ const Debug = imports.src.debug;
 
 const { debug } = Debug;
 
-var YouTubeClient = GObject.registerClass(
-class ClapperYouTubeClient extends Soup.Session
+var YouTubeClient = GObject.registerClass({
+    Signals: {
+        'info-resolved': {
+            param_types: [GObject.TYPE_BOOLEAN]
+        }
+    }
+}, class ClapperYouTubeClient extends Soup.Session
 {
     _init()
     {
         super._init({
             timeout: 5,
         });
+
+        /* videoID of current active download */
+        this.downloadingVideoId = null;
+
+        this.downloadAborted = false;
+        this.lastInfo = null;
     }
 
     getVideoInfoPromise(videoId)
     {
-        return new Promise(async (resolve, reject) => {
-            const url = `https://www.youtube.com/get_video_info?video_id=${videoId}&el=embedded`;
-            let tries = 2;
+        /* If in middle of download and same videoID,
+         * resolve to current download */
+        if(
+            this.downloadingVideoId
+            && this.downloadingVideoId === videoId
+        )
+            return this._getCurrentDownloadPromise();
 
+        return new Promise(async (resolve, reject) => {
+            /* Do not redownload info for the same video */
+            if(this.compareLastVideoId(videoId))
+                return resolve(this.lastInfo);
+
+            this.abort();
+
+            let tries = 2;
             while(tries--) {
                 debug(`obtaining YouTube video info: ${videoId}`);
+                this.downloadingVideoId = videoId;
 
-                const info = await this._getInfoPromise(url).catch(debug);
+                const info = await this._getInfoPromise(videoId).catch(debug);
                 if(!info) {
+                    if(this.downloadAborted)
+                        return reject(new Error('download aborted'));
+
                     debug(`failed, remaining tries: ${tries}`);
                     continue;
                 }
@@ -33,16 +60,31 @@ class ClapperYouTubeClient extends Soup.Session
                 if(
                     !info.playabilityStatus
                     || !info.playabilityStatus.status === 'OK'
-                )
+                ) {
+                    this.emit('info-resolved', false);
+                    this.downloadingVideoId = null;
+
                     return reject(new Error('video is not playable'));
+                }
 
                 /* Check if data contains streaming URIs */
-                if(!info.streamingData)
+                if(!info.streamingData) {
+                    this.emit('info-resolved', false);
+                    this.downloadingVideoId = null;
+
                     return reject(new Error('video response data is missing URIs'));
+                }
+
+                this.lastInfo = info;
+                this.emit('info-resolved', true);
+                this.downloadingVideoId = null;
 
                 return resolve(info);
             }
 
+            this.emit('info-resolved', false);
+            this.downloadingVideoId = null;
+
             reject(new Error('could not obtain YouTube video info'));
         });
     }
@@ -65,9 +107,45 @@ class ClapperYouTubeClient extends Soup.Session
         return combinedStream.url;
     }
 
-    _getInfoPromise(url)
+    compareLastVideoId(videoId)
+    {
+        if(!this.lastInfo)
+            return false;
+
+        if(
+            !this.lastInfo
+            || !this.lastInfo.videoDetails
+            || this.lastInfo.videoDetails.videoId !== videoId
+            /* TODO: check if video expired */
+        )
+            return false;
+
+        return true;
+    }
+
+    _getCurrentDownloadPromise()
+    {
+        debug('resolving after current download finishes');
+
+        return new Promise((resolve, reject) => {
+            const infoResolvedSignal = this.connect('info-resolved', (self, success) => {
+                this.disconnect(infoResolvedSignal);
+
+                debug('current download finished, resolving');
+
+                if(!success)
+                    return reject(new Error('info resolve was unsuccessful'));
+
+                /* At this point new video info is set */
+                resolve(this.lastInfo);
+            });
+        });
+    }
+
+    _getInfoPromise(videoId)
     {
         return new Promise((resolve, reject) => {
+            const url = `https://www.youtube.com/get_video_info?video_id=${videoId}&el=embedded`;
             const message = Soup.Message.new('GET', url);
             let data = '';
 
@@ -85,8 +163,14 @@ class ClapperYouTubeClient extends Soup.Session
 
                 debug('got message response');
 
-                if(msg.status_code !== 200)
-                    return reject(new Error(`response code: ${msg.status_code}`));
+                const statusCode = msg.status_code;
+
+                /* Internal Soup codes mean download abort
+                 * or some other error that cannot be handled */
+                this.downloadAborted = (statusCode < 10);
+
+                if(statusCode !== 200)
+                    return reject(new Error(`response code: ${statusCode}`));
 
                 debug('parsing video info JSON');