feat: Optimize caption sort order (#1661)

* choose best caption

* add comments

* fix linter issue

src/renderer/components/ft-video-player/ft-video-player.js

@@ -140,6 +140,10 @@ export default Vue.extend({
       return this.$store.getters.getUsingElectron
     },
 
+    currentLocale: function () {
+      return this.$store.getters.getCurrentLocale
+    },
+
     defaultPlayback: function () {
       return this.$store.getters.getDefaultPlayback
     },
@@ -1100,6 +1104,47 @@ export default Vue.extend({
       this.determineDefaultQualityDash()
     },
 
+    sortCaptions: function (captionList) {
+      return captionList.sort((captionA, captionB) => {
+        const aCode = captionA.languageCode.split('-') // ex. [en,US]
+        const bCode = captionB.languageCode.split('-')
+        const aName = (captionA.label || captionA.name.simpleText) // ex: english (auto-generated)
+        const bName = (captionB.label || captionB.name.simpleText)
+        const userLocale = this.currentLocale.split(/-|_/) // ex. [en,US]
+        if (aCode[0] === userLocale[0]) { // caption a has same language as user's locale
+          if (bCode[0] === userLocale[0]) { // caption b has same language as user's locale
+            if (bName.search('auto') !== -1) {
+              // prefer caption a: b is auto-generated captions
+              return -1
+            } else if (aName.search('auto') !== -1) {
+              // prefer caption b: a is auto-generated captions
+              return 1
+            } else if (aCode[1] === userLocale[1]) {
+              // prefer caption a: caption a has same county code as user's locale
+              return -1
+            } else if (bCode[1] === userLocale[1]) {
+              // prefer caption b: caption b has same county code as user's locale
+              return 1
+            } else if (aCode[1] === undefined) {
+              // prefer caption a: no country code is better than wrong country code
+              return -1
+            } else if (bCode[1] === undefined) {
+              // prefer caption b: no country code is better than wrong country code
+              return 1
+            }
+          } else {
+            // prefer caption a: b does not match user's language
+            return -1
+          }
+        } else if (bCode[0] === userLocale[0]) {
+          // prefer caption b: a does not match user's language
+          return 1
+        }
+        // sort alphabetically
+        return aName.localeCompare(bName)
+      })
+    },
+
     transformAndInsertCaptions: async function() {
       let captionList
       if (this.captionHybridList[0] instanceof Promise) {
@@ -1109,7 +1154,7 @@ export default Vue.extend({
         captionList = this.captionHybridList
       }
 
-      for (const caption of captionList) {
+      for (const caption of this.sortCaptions(captionList)) {
         this.player.addRemoteTextTrack({
           kind: 'subtitles',
           src: caption.baseUrl || caption.url,