createTimeline: fix viewport and dupelication

src/masto/timelines.ts

@@ -11,114 +11,19 @@ import {
 } from "solid-js";
 import { createStore } from "solid-js/store";
 
-type TimelineFetchTips = {
-  direction?: "new" | "old";
-};
-
 type Timeline = {
   list(params: {
+    /** Return results older than this ID. */
+    readonly maxId?: string;
+    /** Return results newer than this ID. */
+    readonly sinceId?: string;
+    /** Get a list of items with ID greater than this value excluding this ID */
+    readonly minId?: string;
+    /** Maximum number of results to return per page. Defaults to 40. NOTE: Pagination is done with the Link header from the response. */
     readonly limit?: number;
   }): mastodon.Paginator<mastodon.v1.Status[], unknown>;
 };
 
-export function useTimeline(
-  timeline: Accessor<Timeline>,
-  cfg?: {
-    /**
-     * Use full refresh mode. This mode ignores paging, it will refetch the specified number
-     * of toots at every refetch().
-     */
-    fullRefresh?: number;
-  },
-) {
-  let otl: Timeline | undefined;
-  let npager: mastodon.Paginator<mastodon.v1.Status[], unknown> | undefined;
-  let opager: mastodon.Paginator<mastodon.v1.Status[], unknown> | undefined;
-  const [snapshot, { refetch }] = createResource<
-    {
-      records: mastodon.v1.Status[];
-      direction: "new" | "old" | "items";
-      tlChanged: boolean;
-    },
-    [Timeline],
-    TimelineFetchTips | undefined
-  >(
-    () => [timeline()] as const,
-    async ([tl], info) => {
-      let tlChanged = false;
-      if (otl !== tl) {
-        npager = opager = undefined;
-        otl = tl;
-        tlChanged = true;
-      }
-      const fullRefresh = cfg?.fullRefresh;
-      if (typeof fullRefresh !== "undefined") {
-        const records = await tl
-          .list({
-            limit: fullRefresh,
-          })
-          .next();
-        return {
-          direction: "items",
-          records: records.value ?? [],
-          end: records.done,
-          tlChanged,
-        };
-      }
-      const direction =
-        typeof info.refetching !== "boolean"
-          ? (info.refetching?.direction ?? "old")
-          : "old";
-      if (direction === "old") {
-        if (!opager) {
-          opager = tl.list({}).setDirection("next");
-        }
-        const next = await opager.next();
-        return {
-          direction,
-          records: next.value ?? [],
-          end: next.done,
-          tlChanged,
-        };
-      } else {
-        if (!npager) {
-          npager = tl.list({}).setDirection("prev");
-        }
-        const next = await npager.next();
-        const page = next.value ?? [];
-        return { direction, records: page, end: next.done, tlChanged };
-      }
-    },
-  );
-
-  const [store, setStore] = createStore([] as mastodon.v1.Status[]);
-
-  createEffect(() => {
-    const shot = snapshot();
-    if (!shot) return;
-    const { direction, records, tlChanged } = shot;
-    if (tlChanged) {
-      setStore(() => []);
-    }
-    if (direction === "new") {
-      setStore((x) => [...records, ...x]);
-    } else if (direction === "old") {
-      setStore((x) => [...x, ...records]);
-    } else if (direction === "items") {
-      setStore(() => records);
-    }
-  });
-
-  return [
-    store,
-    snapshot,
-    {
-      refetch,
-      mutate: setStore,
-    },
-  ] as const;
-}
-
 export function createTimelineSnapshot(
   timeline: Accessor<Timeline>,
   limit: Accessor<number>,
@@ -176,30 +81,13 @@ export function createTimelineSnapshot(
 export type TimelineFetchDirection = mastodon.Direction;
 
 export type TimelineChunk = {
-  pager: mastodon.Paginator<mastodon.v1.Status[], unknown>;
+  tl: Timeline;
   chunk: readonly mastodon.v1.Status[];
   done?: boolean;
   direction: TimelineFetchDirection;
   limit: number;
 };
 
-function checkOrCreatePager(
-  timeline: Timeline,
-  limit: number,
-  lastPager: TimelineChunk["pager"] | undefined,
-  newDirection: TimelineFetchDirection,
-) {
-  if (!lastPager) {
-    return timeline.list({}).setDirection(newDirection);
-  } else {
-    let pager = lastPager;
-    if (pager.getDirection() !== newDirection) {
-      pager = pager.setDirection(newDirection);
-    }
-    return pager;
-  }
-}
-
 type TreeNode<T> = {
   parent?: TreeNode<T>;
   value: T;
@@ -226,6 +114,38 @@ export function createTimeline(
   const lookup = new ReactiveMap<string, TreeNode<mastodon.v1.Status>>();
   const [threads, setThreads] = createStore([] as mastodon.v1.Status["id"][]);
 
+  let vpMaxId: string | undefined, vpMinId: string | undefined;
+
+  const fetchExtendingPage = async (
+    tl: Timeline,
+    direction: TimelineFetchDirection,
+    limit: number,
+  ) => {
+    switch (direction) {
+      case "next": {
+        const page = await tl
+          .list({ limit, sinceId: vpMaxId })
+          .setDirection(direction)
+          .next();
+        if ((page.value?.length ?? 0) > 0) {
+          vpMaxId = page.value![0].id;
+        }
+        return page;
+      }
+
+      case "prev": {
+        const page = await tl
+          .list({ limit, maxId: vpMinId })
+          .setDirection(direction)
+          .next();
+        if ((page.value?.length ?? 0) > 0) {
+          vpMinId = page.value![page.value!.length - 1].id;
+        }
+        return page;
+      }
+    }
+  };
+
   const [chunk, { refetch }] = createResource(
     () => [timeline(), limit()] as const,
     async (
@@ -237,17 +157,16 @@ export function createTimeline(
     ) => {
       const direction =
         typeof info.refetching === "boolean" ? "prev" : info.refetching;
-      const rebuildTimeline = limit !== info.value?.limit;
-      const pager = rebuildTimeline
-        ? checkOrCreatePager(tl, limit, undefined, direction)
-        : checkOrCreatePager(tl, limit, info.value?.pager, direction);
+      const rebuildTimeline = tl !== info.value?.tl;
       if (rebuildTimeline) {
+        vpMaxId = undefined;
+        vpMinId = undefined;
         lookup.clear();
         setThreads([]);
       }
-      const posts = await pager.next();
+      const posts = await fetchExtendingPage(tl, direction, limit);
       return {
-        pager,
+        tl,
         chunk: posts.value ?? [],
         done: posts.done,
         direction,
@@ -262,33 +181,39 @@ export function createTimeline(
       return;
     }
 
-    console.debug("fetched chunk", chk);
+    const existence = [] as boolean[];
 
-    batch(() => {
-      for (const status of chk.chunk) {
-        lookup.set(status.id, {
-          value: status,
-        });
-      }
+    for (const [idx, status] of chk.chunk.entries()) {
+      existence[idx] = !!untrack(() => lookup.get(status.id));
+      lookup.set(status.id, {
+        value: status,
+      });
+    }
 
-      for (const status of chk.chunk) {
-        const node = lookup.get(status.id)!;
-        if (status.inReplyToId) {
-          const parent = lookup.get(status.inReplyToId);
-          if (parent) {
-            const children = parent.children ?? [];
-            if (!children.find((x) => x.value.id == status.id)) {
-              children.push(node);
-            }
-            parent.children = children;
-            node.parent = parent;
+    for (const status of chk.chunk) {
+      const node = untrack(() => lookup.get(status.id))!;
+      if (status.inReplyToId) {
+        const parent = lookup.get(status.inReplyToId);
+        if (parent) {
+          const children = parent.children ?? [];
+          if (!children.find((x) => x.value.id == status.id)) {
+            children.push(node);
           }
+          parent.children = children;
+          node.parent = parent;
         }
       }
-      if (chk.direction === "next") {
-        setThreads((threads) => [...threads, ...chk.chunk.map((x) => x.id)]);
-      } else if (chk.direction === "prev") {
-        setThreads((threads) => [...chk.chunk.map((x) => x.id), ...threads]);
+    }
+
+    const nThreadIds = chk.chunk
+      .filter((x, i) => !existence[i])
+      .map((x) => x.id);
+
+    batch(() => {
+      if (chk.direction === "prev") {
+        setThreads((threads) => [...threads, ...nThreadIds]);
+      } else if (chk.direction === "next") {
+        setThreads((threads) => [...nThreadIds, ...threads]);
       }
 
       setThreads((threads) =>