[YouTube] Support pageHeaderRenderer and interactiveTabbedHeaderRenderer channel headers

The addition of this support required to turn the isCarouselHeader boolean into
an enum containing all supported channel headers named HeaderType.

Also assert that the page has been fetched where needed to avoid
NullPointerExceptions when the channel page has been not fetched and remove the
getChannelHeaderJson method in YoutubeChannelExtractor, method for which its
code has been moved to its sole usage after the new headers support changes.

Author: AudricV

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubeChannelHelper.java

@@ -219,24 +219,68 @@ private static void checkIfChannelResponseIsValid(@Nonnull final JsonObject json
      */
     public static final class ChannelHeader {
 
+        /**
+         * Types of supported YouTube channel headers.
+         */
+        public enum HeaderType {
+
+            /**
+             * A {@code c4TabbedHeaderRenderer} channel header type.
+             *
+             * <p>
+             * This header is returned on the majority of channels and contains the channel's name,
+             * its banner and its avatar and its subscriber count in most cases.
+             * </p>
+             */
+            C4_TABBED,
+
+            /**
+             * An {@code interactiveTabbedHeaderRenderer} channel header type.
+             *
+             * <p>
+             * This header is returned for gaming topic channels, and only contains the channel's
+             * name, its banner and a poster as its "avatar".
+             * </p>
+             */
+            INTERACTIVE_TABBED,
+
+            /**
+             * A {@code carouselHeaderRenderer} channel header type.
+             *
+             * <p>
+             * This header returns only the channel's name, its avatar and its subscriber count.
+             * </p>
+             */
+            CAROUSEL,
+
+            /**
+             * A {@code pageHeaderRenderer} channel header type.
+             *
+             * <p>
+             * This header returns only the channel's name and its avatar.
+             * </p>
+             */
+            PAGE
+        }
+
         /**
          * The channel header JSON response.
          */
         @Nonnull
         public final JsonObject json;
 
         /**
-         * Whether the header is a {@code carouselHeaderRenderer}.
+         * The type of the channel header.
          *
          * <p>
-         * See the class documentation for more details.
+         * See the documentation of the {@link HeaderType} class for more details.
          * </p>
          */
-        public final boolean isCarouselHeader;
+        public final HeaderType headerType;
 
-        private ChannelHeader(@Nonnull final JsonObject json, final boolean isCarouselHeader) {
+        private ChannelHeader(@Nonnull final JsonObject json, final HeaderType headerType) {
             this.json = json;
-            this.isCarouselHeader = isCarouselHeader;
+            this.headerType = headerType;
         }
     }
 
@@ -254,7 +298,7 @@ public static Optional<ChannelHeader> getChannelHeader(
 
         if (header.has("c4TabbedHeaderRenderer")) {
             return Optional.of(header.getObject("c4TabbedHeaderRenderer"))
-                    .map(json -> new ChannelHeader(json, false));
+                    .map(json -> new ChannelHeader(json, ChannelHeader.HeaderType.C4_TABBED));
         } else if (header.has("carouselHeaderRenderer")) {
             return header.getObject("carouselHeaderRenderer")
                     .getArray("contents")
@@ -264,7 +308,14 @@ public static Optional<ChannelHeader> getChannelHeader(
                     .filter(item -> item.has("topicChannelDetailsRenderer"))
                     .findFirst()
                     .map(item -> item.getObject("topicChannelDetailsRenderer"))
-                    .map(json -> new ChannelHeader(json, true));
+                    .map(json -> new ChannelHeader(json, ChannelHeader.HeaderType.CAROUSEL));
+        } else if (header.has("pageHeaderRenderer")) {
+            return Optional.of(header.getObject("pageHeaderRenderer"))
+                    .map(json -> new ChannelHeader(json, ChannelHeader.HeaderType.PAGE));
+        } else if (header.has("interactiveTabbedHeaderRenderer")) {
+            return Optional.of(header.getObject("interactiveTabbedHeaderRenderer"))
+                    .map(json -> new ChannelHeader(json,
+                            ChannelHeader.HeaderType.INTERACTIVE_TABBED));
         } else {
             return Optional.empty();
         }