Prefetch trickplay images (#445)

Prefetch trickplay images and cache them so that quick scrolling doesn't
require network calls and images will appear significantly faster

Fixes #432

app/src/main/java/com/github/damontecres/wholphin/ui/CoilConfig.kt

@@ -8,8 +8,12 @@ import coil3.compose.setSingletonImageLoaderFactory
 import coil3.disk.DiskCache
 import coil3.disk.directory
 import coil3.memory.MemoryCache
+import coil3.network.CacheStrategy
+import coil3.network.NetworkRequest
+import coil3.network.NetworkResponse
 import coil3.network.cachecontrol.CacheControlCacheStrategy
 import coil3.network.okhttp.OkHttpNetworkFetcherFactory
+import coil3.request.Options
 import coil3.request.crossfade
 import coil3.util.DebugLogger
 import okhttp3.OkHttpClient
@@ -67,10 +71,39 @@ fun CoilConfig(
             .components {
                 add(
                     OkHttpNetworkFetcherFactory(
-                        cacheStrategy = { CacheControlCacheStrategy() },
+                        cacheStrategy = { WholphinCacheStrategy(CacheControlCacheStrategy()) },
                         callFactory = { client },
                     ),
                 )
             }.build()
     }
 }
+
+/**
+ * This [CacheStrategy] always prefers the cached response for Trickplay images,
+ * otherwise the decision is delegated to the provided [CacheStrategy]
+ *
+ * The expectation is that Trickplay images will be prefetched so the cache will always be warm
+ */
+@OptIn(ExperimentalCoilApi::class)
+private class WholphinCacheStrategy(
+    private val delegate: CacheStrategy,
+) : CacheStrategy {
+    override suspend fun read(
+        cacheResponse: NetworkResponse,
+        networkRequest: NetworkRequest,
+        options: Options,
+    ): CacheStrategy.ReadResult =
+        if (networkRequest.url.contains("/Trickplay/")) {
+            CacheStrategy.ReadResult(cacheResponse)
+        } else {
+            delegate.read(cacheResponse, networkRequest, options)
+        }
+
+    override suspend fun write(
+        cacheResponse: NetworkResponse?,
+        networkRequest: NetworkRequest,
+        networkResponse: NetworkResponse,
+        options: Options,
+    ): CacheStrategy.WriteResult = delegate.write(cacheResponse, networkRequest, networkResponse, options)
+}

app/src/main/java/com/github/damontecres/wholphin/ui/playback/PlaybackViewModel.kt

@@ -21,6 +21,8 @@ import androidx.media3.exoplayer.DecoderCounters
 import androidx.media3.exoplayer.DecoderReuseEvaluation
 import androidx.media3.exoplayer.ExoPlayer
 import androidx.media3.exoplayer.analytics.AnalyticsListener
+import coil3.imageLoader
+import coil3.request.ImageRequest
 import com.github.damontecres.wholphin.data.ItemPlaybackDao
 import com.github.damontecres.wholphin.data.ItemPlaybackRepository
 import com.github.damontecres.wholphin.data.ServerRepository
@@ -92,6 +94,7 @@ import org.jellyfin.sdk.model.api.PlayMethod
 import org.jellyfin.sdk.model.api.PlaybackInfoDto
 import org.jellyfin.sdk.model.api.PlaystateCommand
 import org.jellyfin.sdk.model.api.PlaystateMessage
+import org.jellyfin.sdk.model.api.TrickplayInfo
 import org.jellyfin.sdk.model.extensions.inWholeTicks
 import org.jellyfin.sdk.model.extensions.ticks
 import org.jellyfin.sdk.model.serializer.toUUIDOrNull
@@ -99,6 +102,7 @@ import timber.log.Timber
 import java.util.Date
 import java.util.UUID
 import javax.inject.Inject
+import kotlin.time.Duration
 import kotlin.time.Duration.Companion.milliseconds
 import kotlin.time.Duration.Companion.seconds
 
@@ -404,6 +408,13 @@ class PlaybackViewModel
                         ?.get(mediaSource.id)
                         ?.values
                         ?.firstOrNull()
+                trickPlayInfo?.let { trickplayInfo ->
+                    mediaSource.runTimeTicks?.ticks?.let { duration ->
+                        viewModelScope.launchIO {
+                            prefetchTrickplay(duration, trickplayInfo)
+                        }
+                    }
+                }
 
                 val chapters = Chapter.fromDto(base, api)
                 withContext(Dispatchers.Main) {
@@ -723,18 +734,39 @@ class PlaybackViewModel
                 )
             }
 
-        fun getTrickplayUrl(index: Int): String? {
-            val itemId = item.id
-            val mediaSourceId = currentItemPlayback.value?.sourceId
-            val trickPlayInfo = currentMediaInfo.value?.trickPlayInfo ?: return null
-            return api.trickplayApi.getTrickplayTileImageUrl(
-                itemId,
-                trickPlayInfo.width,
-                index,
-                mediaSourceId,
-            )
+        private suspend fun prefetchTrickplay(
+            duration: Duration,
+            trickplayInfo: TrickplayInfo,
+        ) {
+            val tilesPerImage = trickplayInfo.tileWidth * trickplayInfo.tileHeight
+            val totalCount =
+                (duration.inWholeMilliseconds / trickplayInfo.interval).toInt() / tilesPerImage + 1
+            (0..<totalCount).forEach {
+                val url = getTrickplayUrl(it, trickplayInfo)
+                context.imageLoader.enqueue(
+                    ImageRequest
+                        .Builder(context)
+                        .data(url)
+                        .build(),
+                )
+            }
         }
 
+        fun getTrickplayUrl(
+            index: Int,
+            trickPlayInfo: TrickplayInfo? = currentMediaInfo.value?.trickPlayInfo,
+        ): String? =
+            trickPlayInfo?.let {
+                val itemId = item.id
+                val mediaSourceId = currentItemPlayback.value?.sourceId
+                return api.trickplayApi.getTrickplayTileImageUrl(
+                    itemId,
+                    trickPlayInfo.width,
+                    index,
+                    mediaSourceId,
+                )
+            }
+
         override fun onPlaybackStateChanged(playbackState: Int) {
             if (playbackState == Player.STATE_ENDED) {
                 viewModelScope.launchIO {

app/src/main/java/com/github/damontecres/wholphin/ui/playback/SeekPreviewImage.kt

@@ -15,7 +15,6 @@ import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.unit.dp
 import androidx.tv.material3.MaterialTheme
 import coil3.compose.AsyncImage
-import coil3.request.CachePolicy
 import coil3.request.ImageRequest
 import coil3.request.transformations
 import com.github.damontecres.wholphin.ui.CoilTrickplayTransformation
@@ -104,7 +103,6 @@ fun SeekPreviewImage(
                 ImageRequest
                     .Builder(context)
                     .data(previewImageUrl)
-                    .memoryCachePolicy(CachePolicy.ENABLED)
                     .transformations(
                         CoilTrickplayTransformation(
                             widthPx,