| 1 | /** |
| 2 | * The committed subset of a progressively mounted chat order. |
| 3 | * |
| 4 | * History data may arrive before its DOM nodes are revealed. Consumers such as |
| 5 | * the turn navigator subscribe here so every advertised target already exists |
| 6 | * in the document. This is ephemeral view state and is discarded with the |
| 7 | * active chat session. |
| 8 | */ |
| 9 | export class ChatMountedOrder { |
| 10 | private order: readonly string[] = []; |
| 11 | private listeners = new Set<() => void>(); |
| 12 | |
| 13 | getSnapshot = (): readonly string[] => this.order; |
| 14 | |
| 15 | subscribe = (listener: () => void): (() => void) => { |
| 16 | this.listeners.add(listener); |
| 17 | return () => this.listeners.delete(listener); |
| 18 | }; |
| 19 | |
| 20 | publish(next: readonly string[]): void { |
| 21 | if (this.order.length === next.length && this.order.every((key, index) => key === next[index])) return; |
| 22 | this.order = next; |
| 23 | // A synchronous external-store notification may unsubscribe and resubscribe |
| 24 | // while React renders. Iterate a snapshot so the new subscription cannot be |
| 25 | // visited again by the same publication. |
| 26 | for (const listener of [...this.listeners]) listener(); |
| 27 | } |
| 28 | |
| 29 | dispose(): void { |
| 30 | this.order = []; |
| 31 | this.listeners.clear(); |
| 32 | } |
| 33 | } |
| 34 | |
| 35 | export const CHAT_HISTORY_MOUNT_BATCH = 24; |
| 36 | |
| 37 | export function reconcileMountedOrder(current: readonly string[], order: readonly string[]): readonly string[] { |
| 38 | if (!current.length) return order; |
| 39 | const start = order.indexOf(current[0]); |
| 40 | const contiguous = start >= 0 && current.every((key, index) => order[start + index] === key); |
| 41 | if (!contiguous) return order; |
| 42 | const suffix = order.slice(start + current.length); |
| 43 | return suffix.length ? [...current, ...suffix] : current; |
| 44 | } |
| 45 | |
| 46 | /** Add the nearest leading history nodes while keeping the mounted suffix intact. */ |
| 47 | export function revealEarlierMountedOrder(current: readonly string[], order: readonly string[]): readonly string[] { |
| 48 | if (!current.length) return order; |
| 49 | const start = order.indexOf(current[0]); |
| 50 | const contiguous = start >= 0 && current.every((key, index) => order[start + index] === key); |
| 51 | if (!contiguous) return order; |
| 52 | const chunkStart = Math.max(0, start - CHAT_HISTORY_MOUNT_BATCH); |
| 53 | const suffix = order.slice(start + current.length); |
| 54 | if (chunkStart === start && !suffix.length) return current; |
| 55 | return [...order.slice(chunkStart, start), ...current, ...suffix]; |
| 56 | } |
| 57 |