snapshot of https://github.com/raimohanska/ourboard.git (master, 2026-09-23; blobs > 131072B omitted)

common/src/action-folding.ts

@@ -0,0 +1,87 @@
+import { arrayEquals, arrayIdAndKeysMatch, arrayIdMatch, idsOf } from "./arrays"
+import {
+    AppEvent,
+    BoardHistoryEntry,
+    CURSOR_POSITIONS_ACTION_TYPE,
+    MoveItem,
+    isBoardHistoryEntry,
+    isSameUser,
+} from "./domain"
+
+type FoldOptions = {
+    cursorsOnly?: boolean
+}
+
+const defaultOptions = {
+    foldAddUpdate: true,
+    cursorsOnly: false,
+}
+
+export const CURSORS_ONLY: FoldOptions = { cursorsOnly: true }
+
+export function foldActions(a: AppEvent, b: AppEvent, options: FoldOptions = defaultOptions): AppEvent | null {
+    if (isBoardHistoryEntry(a) && isBoardHistoryEntry(b)) {
+        if (options.cursorsOnly) return null
+        if (!isSameUser(a.user, b.user)) return null
+        const folded = foldActions_(a, b, options)
+        if (!folded) return null
+        const firstSerial = a.firstSerial ? a.firstSerial : a.serial
+        const serial = b.serial
+        return { ...(folded as BoardHistoryEntry), serial, firstSerial } as BoardHistoryEntry
+    } else {
+        return foldActions_(a, b, options)
+    }
+}
+/*
+Folding can be done if in any given state S, applying actions A and B consecutively can be replaced with a single action C.
+This function should return that composite action or null if folding is not possible.
+*/
+export function foldActions_(a: AppEvent, b: AppEvent, options: FoldOptions = defaultOptions): AppEvent | null {
+    if (a.action === CURSOR_POSITIONS_ACTION_TYPE && b.action === CURSOR_POSITIONS_ACTION_TYPE) {
+        return b
+    }
+    if (a.action === "cursor.move" && b.action === "cursor.move" && b.boardId === a.boardId) {
+        return b // This is a local cursor move
+    }
+    if (options.cursorsOnly) return null
+
+    if (isBoardHistoryEntry(a) && isBoardHistoryEntry(b)) {
+        if (!isSameUser(a.user, b.user)) return null
+    }
+    if (a.action === "item.front") {
+        if (b.action === "item.front" && b.boardId === a.boardId && arrayEquals(b.itemIds, a.itemIds)) return b
+    } else if (a.action === "item.move") {
+        if (b.action === "item.move" && b.boardId === a.boardId && everyMovedItemMatches(b, a)) return b
+    } else if (a.action === "item.update") {
+        if (
+            b.action === "item.update" &&
+            b.boardId === a.boardId &&
+            arrayIdAndKeysMatch(b.items, a.items) &&
+            arrayIdAndKeysMatch(b.connections ?? [], a.connections ?? [])
+        ) {
+            return b
+        }
+    } else if (a.action === "item.lock" || a.action === "item.unlock") {
+        if (b.action === a.action && b.boardId === a.boardId && b.itemId === a.itemId) return b
+    } else if (a.action === "connection.modify" && b.action === "connection.modify") {
+        if (arrayIdMatch(a.connections, b.connections)) return b
+    } else if (a.action === "connection.modify" && b.action === "connection.delete") {
+        if (arrayEquals(b.connectionIds, idsOf(a.connections))) return b
+    }
+    return null
+}
+
+function everyMovedItemMatches(evt: MoveItem, evt2: MoveItem) {
+    return arrayIdMatch(evt.items, evt2.items) && arrayIdMatch(evt.connections, evt2.connections)
+}
+
+export function addOrReplaceEvent<E extends AppEvent>(event: E, q: E[], options: FoldOptions = defaultOptions): E[] {
+    for (let i = 0; i < q.length; i++) {
+        let eventInQueue = q[i]
+        const folded = foldActions(eventInQueue, event, options)
+        if (folded) {
+            return [...q.slice(0, i), folded, ...q.slice(i + 1)] as E[]
+        }
+    }
+    return q.concat(event)
+}