feat(LocalFeedRepository): throttle feed extraction

Throttles the local feed extration in-order to avoid rate-limiting.
This is done, similary to NewPipe, by introducting an articificial
delay every 50 fetched feeds of on average 1 second. These values
may have to be changed in the future.

Ref: #6941 (comment)

app/src/main/java/com/github/libretube/repo/LocalFeedRepository.kt

@@ -12,13 +12,15 @@ import com.github.libretube.extensions.parallelMap
 import com.github.libretube.helpers.NewPipeExtractorInstance
 import com.github.libretube.helpers.PreferenceHelper
 import com.github.libretube.ui.dialogs.ShareDialog.Companion.YOUTUBE_FRONTEND_URL
+import kotlinx.coroutines.delay
 import org.schabi.newpipe.extractor.channel.ChannelInfo
 import org.schabi.newpipe.extractor.channel.tabs.ChannelTabInfo
 import org.schabi.newpipe.extractor.channel.tabs.ChannelTabs
 import org.schabi.newpipe.extractor.feed.FeedInfo
 import org.schabi.newpipe.extractor.stream.StreamInfoItem
 import java.time.Duration
 import java.time.Instant
+import java.util.concurrent.atomic.AtomicInteger
 
 class LocalFeedRepository : FeedRepository {
     private val relevantTabs =
@@ -59,6 +61,7 @@ class LocalFeedRepository : FeedRepository {
     }
 
     private suspend fun refreshFeed(channelIds: List<String>, minimumDateMillis: Long) {
+        val extractionCount = AtomicInteger()
         for (channelIdChunk in channelIds.chunked(CHUNK_SIZE)) {
             val collectedFeedItems = channelIdChunk.parallelMap { channelId ->
                 try {
@@ -70,6 +73,12 @@ class LocalFeedRepository : FeedRepository {
             }.filterNotNull().flatten().map(StreamItem::toFeedItem)
 
             DatabaseHolder.Database.feedDao().insertAll(collectedFeedItems)
+
+            // throttle feed extraction to avoid rate limiting
+            val count = extractionCount.getAndIncrement()
+            if (count != 0 && count % BATCH_SIZE == 0) {
+                delay(BATCH_DELAY.random())
+            }
         }
     }
 
@@ -106,6 +115,14 @@ class LocalFeedRepository : FeedRepository {
 
     companion object {
         private const val CHUNK_SIZE = 2
+        /**
+         * Maximum amount of feeds that should be fetched together, before a delay should be applied.
+         */
+        private const val BATCH_SIZE = 50
+        /**
+         * Millisecond delay between two consecutive batches to avoid throttling.
+         */
+        private val BATCH_DELAY = (500L..1500L)
         private const val MAX_FEED_AGE_DAYS = 30L // 30 days
     }
 }