Refactor ExportPlaylist to use more idiomatic kotlin code

Author: Yevhen Babiichuk (DustDFG)

app/src/main/java/org/schabi/newpipe/local/playlist/ExportPlaylist.kt

@@ -1,3 +1,8 @@
+/*
+ * SPDX-FileCopyrightText: 2025 NewPipe contributors <https://newpipe.net>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
 package org.schabi.newpipe.local.playlist
 
 import android.content.Context
@@ -21,11 +26,7 @@ fun export(
     }
 }
 
-fun exportWithTitles(
-    playlist: List<PlaylistStreamEntry>,
-    context: Context
-): String {
-
+private fun exportWithTitles(playlist: List<PlaylistStreamEntry>, context: Context): String {
     return playlist.asSequence()
         .map { it.streamEntity }
         .map { entity ->
@@ -38,18 +39,14 @@ fun exportWithTitles(
         .joinToString(separator = "\n")
 }
 
-fun exportJustUrls(playlist: List<PlaylistStreamEntry>): String {
-
-    return playlist.asSequence()
-        .map { it.streamEntity.url }
-        .joinToString(separator = "\n")
+private fun exportJustUrls(playlist: List<PlaylistStreamEntry>): String {
+    return playlist.joinToString(separator = "\n") { it.streamEntity.url }
 }
 
-fun exportAsYoutubeTempPlaylist(playlist: List<PlaylistStreamEntry>): String {
+private fun exportAsYoutubeTempPlaylist(playlist: List<PlaylistStreamEntry>): String {
 
     val videoIDs = playlist.asReversed().asSequence()
-        .map { it.streamEntity.url }
-        .mapNotNull(::getYouTubeId)
+        .mapNotNull { getYouTubeId(it.streamEntity.url) }
         .take(50) // YouTube limitation: temp playlists can't have more than 50 items
         .toList()
         .asReversed()
@@ -58,15 +55,15 @@ fun exportAsYoutubeTempPlaylist(playlist: List<PlaylistStreamEntry>): String {
     return "https://www.youtube.com/watch_videos?video_ids=$videoIDs"
 }
 
-val linkHandler: YoutubeStreamLinkHandlerFactory = YoutubeStreamLinkHandlerFactory.getInstance()
+private val linkHandler: YoutubeStreamLinkHandlerFactory = YoutubeStreamLinkHandlerFactory.getInstance()
 
 /**
  * Gets the video id from a YouTube URL.
  *
  * @param url YouTube URL
  * @return the video id
  */
-fun getYouTubeId(url: String): String? {
+private fun getYouTubeId(url: String): String? {
 
     return try { linkHandler.getId(url) } catch (e: ParsingException) { null }
 }

app/src/test/java/org/schabi/newpipe/local/playlist/ExportPlaylistTest.kt

@@ -1,3 +1,8 @@
+/*
+ * SPDX-FileCopyrightText: 2025 NewPipe contributors <https://newpipe.net>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
 package org.schabi.newpipe.local.playlist
 
 import android.content.Context
@@ -9,7 +14,6 @@ import org.schabi.newpipe.database.stream.model.StreamEntity
 import org.schabi.newpipe.extractor.stream.StreamType
 import org.schabi.newpipe.local.playlist.PlayListShareMode.JUST_URLS
 import org.schabi.newpipe.local.playlist.PlayListShareMode.YOUTUBE_TEMP_PLAYLIST
-import java.util.stream.Stream
 
 class ExportPlaylistTest {
 
@@ -41,9 +45,7 @@ class ExportPlaylistTest {
          */
 
         val playlist = asPlaylist(
-            (10..70)
-                .map { id -> "https://www.youtube.com/watch?v=aaaaaaaaa$id" } // YouTube video IDs are 11 characters long
-                .stream()
+            (10..70).map { id -> "https://www.youtube.com/watch?v=aaaaaaaaa$id" } // YouTube video IDs are 11 characters long
         )
 
         val url = export(YOUTUBE_TEMP_PLAYLIST, playlist, mock(Context::class.java))
@@ -78,13 +80,11 @@ class ExportPlaylistTest {
 }
 
 fun asPlaylist(vararg urls: String): List<PlaylistStreamEntry> {
-    return asPlaylist(Stream.of(*urls))
+    return asPlaylist(listOf(*urls))
 }
 
-fun asPlaylist(urls: Stream<String>): List<PlaylistStreamEntry> {
-    return urls
-        .map { url: String -> newPlaylistStreamEntry(url) }
-        .toList()
+fun asPlaylist(urls: List<String>): List<PlaylistStreamEntry> {
+    return urls.map { newPlaylistStreamEntry(it) }
 }
 
 fun newPlaylistStreamEntry(url: String): PlaylistStreamEntry {