Move automatic text track selection code to AutomaticTrackSelection helper

Source/core/html/track/AutomaticTrackSelection.cpp

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+#include "core/html/track/AutomaticTrackSelection.h"
+
+#include "core/html/track/TextTrack.h"
+#include "core/html/track/TextTrackList.h"
+#include "platform/Language.h"
+
+namespace blink {
+
+class TrackGroup {
+    STACK_ALLOCATED();
+public:
+    enum GroupKind {
+        CaptionsAndSubtitles,
+        Description,
+        Chapter,
+        Metadata
+    };
+
+    explicit TrackGroup(GroupKind kind)
+        : visibleTrack(nullptr)
+        , defaultTrack(nullptr)
+        , kind(kind)
+        , hasSrcLang(false)
+    {
+    }
+
+    WillBeHeapVector<RefPtrWillBeMember<TextTrack>> tracks;
+    RefPtrWillBeMember<TextTrack> visibleTrack;
+    RefPtrWillBeMember<TextTrack> defaultTrack;
+    GroupKind kind;
+    bool hasSrcLang;
+};
+
+static int textTrackLanguageSelectionScore(const TextTrack& track)
+{
+    if (track.language().isEmpty())
+        return 0;
+
+    Vector<AtomicString> languages = userPreferredLanguages();
+    size_t languageMatchIndex = indexOfBestMatchingLanguageInList(track.language(), languages);
+    if (languageMatchIndex >= languages.size())
+        return 0;
+
+    return languages.size() - languageMatchIndex;
+}
+
+static int textTrackSelectionScore(const TextTrack& track)
+{
+    if (track.kind() != TextTrack::captionsKeyword() && track.kind() != TextTrack::subtitlesKeyword())
+        return 0;
+
+    return textTrackLanguageSelectionScore(track);
+}
+
+AutomaticTrackSelection::AutomaticTrackSelection(const Configuration& configuration)
+    : m_configuration(configuration)
+{
+}
+
+void AutomaticTrackSelection::performAutomaticTextTrackSelection(const TrackGroup& group)
+{
+    ASSERT(group.tracks.size());
+
+    // First, find the track in the group that should be enabled (if any).
+    WillBeHeapVector<RefPtrWillBeMember<TextTrack>> currentlyEnabledTracks;
+    RefPtrWillBeRawPtr<TextTrack> trackToEnable = nullptr;
+    RefPtrWillBeRawPtr<TextTrack> defaultTrack = nullptr;
+    RefPtrWillBeRawPtr<TextTrack> fallbackTrack = nullptr;
+    int highestTrackScore = 0;
+    for (size_t i = 0; i < group.tracks.size(); ++i) {
+        RefPtrWillBeRawPtr<TextTrack> textTrack = group.tracks[i];
+
+        if (m_configuration.disableCurrentlyEnabledTracks && textTrack->mode() == TextTrack::showingKeyword())
+            currentlyEnabledTracks.append(textTrack);
+
+        int trackScore = textTrackSelectionScore(*textTrack);
+        if (trackScore) {
+            // * If the text track kind is { [subtitles or captions] [descriptions] } and the user has indicated an interest in having a
+            // track with this text track kind, text track language, and text track label enabled, and there is no
+            // other text track in the media element's list of text tracks with a text track kind of either subtitles
+            // or captions whose text track mode is showing
+            // ...
+            // * If the text track kind is chapters and the text track language is one that the user agent has reason
+            // to believe is appropriate for the user, and there is no other text track in the media element's list of
+            // text tracks with a text track kind of chapters whose text track mode is showing
+            //    Let the text track mode be showing.
+            if (trackScore > highestTrackScore) {
+                highestTrackScore = trackScore;
+                trackToEnable = textTrack;
+            }
+
+            if (!defaultTrack && textTrack->isDefault())
+                defaultTrack = textTrack;
+            if (!defaultTrack && !fallbackTrack)
+                fallbackTrack = textTrack;
+        } else if (!group.visibleTrack && !defaultTrack && textTrack->isDefault()) {
+            // * If the track element has a default attribute specified, and there is no other text track in the media
+            // element's list of text tracks whose text track mode is showing or showing by default
+            //    Let the text track mode be showing by default.
+            defaultTrack = textTrack;
+        }
+    }
+
+    if (!trackToEnable && defaultTrack)
+        trackToEnable = defaultTrack;
+
+    // If no track matches the user's preferred language and non was marked 'default', enable the first track
+    // because the user has explicitly stated a preference for this kind of track.
+    if (!fallbackTrack && m_configuration.forceEnableSubtitleOrCaptionTrack && group.kind == TrackGroup::CaptionsAndSubtitles)
+        fallbackTrack = group.tracks[0];
+
+    if (!trackToEnable && fallbackTrack)
+        trackToEnable = fallbackTrack;
+
+    if (currentlyEnabledTracks.size()) {
+        for (size_t i = 0; i < currentlyEnabledTracks.size(); ++i) {
+            RefPtrWillBeRawPtr<TextTrack> textTrack = currentlyEnabledTracks[i];
+            if (textTrack != trackToEnable)
+                textTrack->setMode(TextTrack::disabledKeyword());
+        }
+    }
+
+    if (trackToEnable)
+        trackToEnable->setMode(TextTrack::showingKeyword());
+}
+
+void AutomaticTrackSelection::enableDefaultMetadataTextTracks(const TrackGroup& group)
+{
+    ASSERT(group.tracks.size());
+
+    // https://html.spec.whatwg.org/multipage/embedded-content.html#honor-user-preferences-for-automatic-text-track-selection
+
+    // 4. If there are any text tracks in the media element's list of text
+    // tracks whose text track kind is metadata that correspond to track
+    // elements with a default attribute set whose text track mode is set to
+    // disabled, then set the text track mode of all such tracks to hidden
+    for (auto& textTrack : group.tracks) {
+        if (textTrack->mode() != TextTrack::disabledKeyword())
+            continue;
+        if (!textTrack->isDefault())
+            continue;
+        textTrack->setMode(TextTrack::hiddenKeyword());
+    }
+}
+
+void AutomaticTrackSelection::perform(TextTrackList& textTracks)
+{
+    TrackGroup captionAndSubtitleTracks(TrackGroup::CaptionsAndSubtitles);
+    TrackGroup descriptionTracks(TrackGroup::Description);
+    TrackGroup chapterTracks(TrackGroup::Chapter);
+    TrackGroup metadataTracks(TrackGroup::Metadata);
+
+    for (size_t i = 0; i < textTracks.length(); ++i) {
+        RefPtrWillBeRawPtr<TextTrack> textTrack = textTracks.item(i);
+        if (!textTrack)
+            continue;
+
+        String kind = textTrack->kind();
+        TrackGroup* currentGroup;
+        if (kind == TextTrack::subtitlesKeyword() || kind == TextTrack::captionsKeyword()) {
+            currentGroup = &captionAndSubtitleTracks;
+        } else if (kind == TextTrack::descriptionsKeyword()) {
+            currentGroup = &descriptionTracks;
+        } else if (kind == TextTrack::chaptersKeyword()) {
+            currentGroup = &chapterTracks;
+        } else {
+            ASSERT(kind == TextTrack::metadataKeyword());
+            currentGroup = &metadataTracks;
+        }
+
+        if (!currentGroup->visibleTrack && textTrack->mode() == TextTrack::showingKeyword())
+            currentGroup->visibleTrack = textTrack;
+        if (!currentGroup->defaultTrack && textTrack->isDefault())
+            currentGroup->defaultTrack = textTrack;
+
+        // Do not add this track to the group if it has already been automatically configured
+        // as we only want to perform selection once per track so that adding another track
+        // after the initial configuration doesn't reconfigure every track - only those that
+        // should be changed by the new addition. For example all metadata tracks are
+        // disabled by default, and we don't want a track that has been enabled by script
+        // to be disabled automatically when a new metadata track is added later.
+        if (textTrack->hasBeenConfigured())
+            continue;
+
+        if (textTrack->language().length())
+            currentGroup->hasSrcLang = true;
+        currentGroup->tracks.append(textTrack);
+    }
+
+    if (captionAndSubtitleTracks.tracks.size())
+        performAutomaticTextTrackSelection(captionAndSubtitleTracks);
+    if (descriptionTracks.tracks.size())
+        performAutomaticTextTrackSelection(descriptionTracks);
+    if (chapterTracks.tracks.size())
+        performAutomaticTextTrackSelection(chapterTracks);
+    if (metadataTracks.tracks.size())
+        enableDefaultMetadataTextTracks(metadataTracks);
+}
+
+} // namespace blink