From fb9ed3ed073c21948a93bf49c1baca7ce76eb8e0 Mon Sep 17 00:00:00 2001
From: Igor Zolotarenko <zolotarenko.i.r@gmail.com>
Date: Mon, 18 Dec 2023 20:07:27 +0200
Subject: [PATCH] Fix bug.

---
 .../p2p-media-loader-core/src/linked-map.ts   |  9 +++
 packages/p2p-media-loader-core/src/types.d.ts |  2 +-
 .../src/segment-manager.ts                    | 60 ++++++++++++-------
 .../src/stream-utils.ts                       |  9 ++-
 4 files changed, 52 insertions(+), 28 deletions(-)

diff --git a/packages/p2p-media-loader-core/src/linked-map.ts b/packages/p2p-media-loader-core/src/linked-map.ts
index f1827daf..3af745ec 100644
--- a/packages/p2p-media-loader-core/src/linked-map.ts
+++ b/packages/p2p-media-loader-core/src/linked-map.ts
@@ -68,6 +68,15 @@ export class LinkedMap<K, V extends object> {
     }
   }
 
+  *valuesBackwards(key?: K) {
+    let value = key ? this.map.get(key) : this._last;
+    if (value === undefined) return;
+    while (value?.item !== undefined) {
+      yield value.item[1];
+      value = value.prev;
+    }
+  }
+
   *keys(): Generator<K> {
     let value = this._first;
     if (value === undefined) return;
diff --git a/packages/p2p-media-loader-core/src/types.d.ts b/packages/p2p-media-loader-core/src/types.d.ts
index d555a881..e03ab496 100644
--- a/packages/p2p-media-loader-core/src/types.d.ts
+++ b/packages/p2p-media-loader-core/src/types.d.ts
@@ -26,7 +26,7 @@ export type Stream = {
 
 export type ReadonlyLinkedMap<K, V extends object> = Pick<
   LinkedMap<K, V>,
-  "has" | "keys" | "values" | "size"
+  "has" | "keys" | "values" | "valuesBackwards" | "size"
 >;
 
 export type StreamWithSegments<
diff --git a/packages/p2p-media-loader-shaka/src/segment-manager.ts b/packages/p2p-media-loader-shaka/src/segment-manager.ts
index 2a3c2185..870b56a5 100644
--- a/packages/p2p-media-loader-shaka/src/segment-manager.ts
+++ b/packages/p2p-media-loader-shaka/src/segment-manager.ts
@@ -5,6 +5,7 @@ import {
   StreamWithReadonlySegments,
   SegmentBase,
   StreamType,
+  ReadonlyLinkedMap,
 } from "p2p-media-loader-core";
 
 export class SegmentManager {
@@ -72,6 +73,7 @@ export class SegmentManager {
       staleSegmentsIds.delete(segmentLocalId);
     }
 
+    if (!newSegments.length && !staleSegmentsIds.size) return;
     this.core.updateStream(managerStream.localId, newSegments, [
       ...staleSegmentsIds,
     ]);
@@ -81,52 +83,66 @@ export class SegmentManager {
     managerStream: StreamWithReadonlySegments<Stream>,
     segmentReferences: shaka.media.SegmentReference[]
   ) {
-    const segments = [...managerStream.segments.values()];
+    const { segments } = managerStream;
     const lastMediaSequence = Utils.getStreamLastMediaSequence(managerStream);
 
     const newSegments: SegmentBase[] = [];
-    if (segments.length === 0) {
+    if (segments.size === 0) {
       const firstReferenceMediaSequence =
         lastMediaSequence === undefined
           ? 0
           : lastMediaSequence - segmentReferences.length + 1;
-      segmentReferences.forEach((reference, index) => {
+
+      for (const [index, reference] of segmentReferences.entries()) {
         const segment = Utils.createSegment({
           segmentReference: reference,
           externalId: firstReferenceMediaSequence + index,
         });
         newSegments.push(segment);
-      });
+      }
       this.core.updateStream(managerStream.localId, newSegments);
       return;
     }
 
-    let index = lastMediaSequence ?? 0;
-    const startSize = managerStream.segments.size;
+    if (!lastMediaSequence) return;
+    let mediaSequence = lastMediaSequence;
 
-    for (let i = segmentReferences.length - 1; i >= 0; i--) {
-      const reference = segmentReferences[i];
+    for (const reference of itemsBackwards(segmentReferences)) {
       const localId = Utils.getSegmentLocalIdFromReference(reference);
-      if (!managerStream.segments.has(localId)) {
-        const segment = Utils.createSegment({
-          localId,
-          segmentReference: reference,
-          externalId: index,
-        });
-        newSegments.push(segment);
-        index--;
-      } else {
-        break;
-      }
+      if (segments.has(localId)) break;
+      const segment = Utils.createSegment({
+        localId,
+        segmentReference: reference,
+        externalId: mediaSequence,
+      });
+      newSegments.push(segment);
+      mediaSequence--;
     }
     newSegments.reverse();
 
-    const deleteCount = managerStream.segments.size - startSize;
     const staleSegmentIds: string[] = [];
-    for (let i = 0; i < deleteCount; i++) {
-      const segment = segments[i];
+    const amountToDelete = newSegments.length;
+    for (const segment of nSegmentsBackwards(segments, amountToDelete)) {
       staleSegmentIds.push(segment.localId);
     }
+
+    if (!newSegments.length && !staleSegmentIds.length) return;
     this.core.updateStream(managerStream.localId, newSegments, staleSegmentIds);
   }
 }
+
+function* itemsBackwards<T>(items: T[]) {
+  for (let i = items.length - 1; i >= 0; i--) yield items[i];
+}
+
+function* nSegmentsBackwards(
+  segments: ReadonlyLinkedMap<string, SegmentBase>,
+  amount: number
+) {
+  let i = 0;
+  for (const segment of segments.valuesBackwards()) {
+    if (i >= amount) break;
+    yield segment;
+    i--;
+  }
+}
diff --git a/packages/p2p-media-loader-shaka/src/stream-utils.ts b/packages/p2p-media-loader-shaka/src/stream-utils.ts
index a0a955a1..4a84c8a7 100644
--- a/packages/p2p-media-loader-shaka/src/stream-utils.ts
+++ b/packages/p2p-media-loader-shaka/src/stream-utils.ts
@@ -80,10 +80,9 @@ export function getStreamLastMediaSequence(
 ): number | undefined {
   const { shakaStream } = stream;
   const map = shakaStream.mediaSequenceTimeMap;
+  if (!map) return;
 
-  if (map) {
-    const firstMediaSequence = map.keys().next().value as number | undefined;
-    if (firstMediaSequence === undefined) return;
-    return firstMediaSequence + map.size - 1;
-  }
+  const firstMediaSequence = map.keys().next().value as number | undefined;
+  if (firstMediaSequence === undefined) return;
+  return firstMediaSequence + map.size - 1;
 }