[YouTube] Add base implementation for show InfoItems

As there are multiple show UI elements which share a lot of common data, a base
implementation, an abstract class named YoutubeBaseShowInfoItemExtractor, has
been created to handle common cases.

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/extractors/YoutubeBaseShowInfoItemExtractor.java

@@ -0,0 +1,65 @@
+package org.schabi.newpipe.extractor.services.youtube.extractors;
+
+import com.grack.nanojson.JsonObject;
+import org.schabi.newpipe.extractor.Image;
+import org.schabi.newpipe.extractor.exceptions.ParsingException;
+import org.schabi.newpipe.extractor.playlist.PlaylistInfoItemExtractor;
+import org.schabi.newpipe.extractor.utils.Utils;
+
+import javax.annotation.Nonnull;
+import java.util.List;
+
+import static org.schabi.newpipe.extractor.services.youtube.YoutubeParsingHelper.getTextFromObject;
+import static org.schabi.newpipe.extractor.services.youtube.YoutubeParsingHelper.getThumbnailsFromInfoItem;
+import static org.schabi.newpipe.extractor.services.youtube.YoutubeParsingHelper.getUrlFromNavigationEndpoint;
+
+/**
+ * The base {@link PlaylistInfoItemExtractor} for shows playlists UI elements.
+ */
+abstract class YoutubeBaseShowInfoItemExtractor implements PlaylistInfoItemExtractor {
+
+    @Nonnull
+    protected final JsonObject showRenderer;
+
+    YoutubeBaseShowInfoItemExtractor(@Nonnull final JsonObject showRenderer) {
+        this.showRenderer = showRenderer;
+    }
+
+    @Override
+    public String getName() throws ParsingException {
+        return showRenderer.getString("title");
+    }
+
+    @Override
+    public String getUrl() throws ParsingException {
+        return getUrlFromNavigationEndpoint(showRenderer.getObject("navigationEndpoint"));
+    }
+
+    @Nonnull
+    @Override
+    public List<Image> getThumbnails() throws ParsingException {
+        return getThumbnailsFromInfoItem(showRenderer.getObject("thumbnailRenderer")
+                .getObject("showCustomThumbnailRenderer"));
+    }
+
+    @Override
+    public long getStreamCount() throws ParsingException {
+        // The stream count should be always returned in the first text object for English
+        // localizations, but the complete text is parsed for reliability purposes
+        final String streamCountText = getTextFromObject(
+                showRenderer.getObject("thumbnailOverlays")
+                        .getObject("thumbnailOverlayBottomPanelRenderer")
+                        .getObject("text"));
+        if (streamCountText == null) {
+            throw new ParsingException("Could not get stream count");
+        }
+
+        try {
+            // The data returned could be a human/shortened number, but no show with more than 1000
+            // videos has been found at the time this code was written
+            return Long.parseLong(Utils.removeNonDigitCharacters(streamCountText));
+        } catch (final NumberFormatException e) {
+            throw new ParsingException("Could not convert stream count to a long", e);
+        }
+    }
+}