// Klient-adapter: kernel-transport (@siax/collaboration CollaborationTransport)
// över 0pts host-API (/api/admin/order-notes). Admin-ytan pratar ALDRIG med
// fetch direkt — allt går genom denna adapter, så offline-läge och
// versionskonflikter hanteras på ETT ställe:
//  - offline: send() är ett medvetet NO-OP som kastar OfflineError — utkastet
//    behålls i UI:t och användaren får en varning. Ingen tyst förlust.
//  - 409: ConflictError med serverns aktuella version -> UI laddar om.
// Presence går via kernelns upsertPresence (status offline/online per författare).
import {
  nextLamportClock,
  upsertPresence,
  type CollaborationOperation,
  type CollaborationTransport,
  type PresenceState,
} from "@siax/collaboration";

export interface OrderNoteDto {
  note_id: string;
  order_id: string;
  author_id: string;
  body: string;
  version: number;
  clock: number;
  updated_at: string;
}

export class OfflineError extends Error {
  constructor() {
    super("Offline: note change was NOT sent — draft kept locally, nothing lost");
    this.name = "OfflineError";
  }
}

export class ConflictError extends Error {
  constructor(
    public readonly noteId: string,
    public readonly currentVersion: number,
  ) {
    super(`Note ${noteId} changed server-side (current version ${currentVersion})`);
    this.name = "ConflictError";
  }
}

export class OrderNotesTransport implements CollaborationTransport<{ body: string }> {
  private listeners = new Set<(op: CollaborationOperation<{ body: string }>) => void>();
  private presenceListeners = new Set<(p: PresenceState) => void>();
  private presence = new Map<string, PresenceState>();
  private localClock = 0;
  private offline = false;

  constructor(readonly actorId: string) {}

  setOffline(offline: boolean): void {
    this.offline = offline;
    this.setPresence({ participantId: this.actorId, status: offline ? "offline" : "online" });
  }

  isOffline(): boolean {
    return this.offline;
  }

  getPresence(): PresenceState[] {
    return [...this.presence.values()];
  }

  setPresence(presence: PresenceState): void {
    this.presence = upsertPresence(this.presence, presence);
    for (const l of this.presenceListeners) l(presence);
  }

  async connect(): Promise<void> {
    this.setOffline(false);
  }

  async disconnect(): Promise<void> {
    this.setOffline(true);
  }

  onOperation(listener: (op: CollaborationOperation<{ body: string }>) => void): () => void {
    this.listeners.add(listener);
    return () => this.listeners.delete(listener);
  }

  onPresence(listener: (p: PresenceState) => void): () => void {
    this.presenceListeners.add(listener);
    return () => this.presenceListeners.delete(listener);
  }

  /** Replay a server op into local listeners + advance the Lamport clock. */
  observeRemote(operation: CollaborationOperation<{ body: string }>): void {
    this.localClock = nextLamportClock(this.localClock, operation.clock);
    this.setPresence({
      participantId: operation.actorId,
      status: this.presence.get(operation.actorId)?.status ?? "online",
    });
    for (const l of this.listeners) l(operation);
  }

  async send(operation: CollaborationOperation<{ body: string }>): Promise<void> {
    if (this.offline) throw new OfflineError();
    this.localClock = nextLamportClock(this.localClock, operation.clock);
    for (const l of this.listeners) l(operation);
  }
}

export interface NotesApiResult {
  notes: OrderNoteDto[];
  /** Version per note — the optimistic-concurrency handle the UI PATCHes with. */
  versions: Map<string, number>;
}

export class OrderNotesClient {
  readonly transport: OrderNotesTransport;

  constructor(actorId: string) {
    this.transport = new OrderNotesTransport(actorId);
  }

  async load(orderId: string): Promise<NotesApiResult> {
    const res = await fetch(`/api/admin/order-notes?order_id=${encodeURIComponent(orderId)}`, {
      cache: "no-store",
    });
    if (!res.ok) throw new Error(`load failed: ${res.status}`);
    const body = (await res.json()) as { notes: OrderNoteDto[] };
    const versions = new Map<string, number>();
    for (const note of body.notes) {
      versions.set(note.note_id, note.version);
      this.transport.observeRemote({
        id: note.note_id,
        actorId: note.author_id,
        clock: note.clock,
        type: "note.upsert",
        payload: { body: note.body },
      });
    }
    return { notes: body.notes, versions };
  }

  async add(orderId: string, body: string): Promise<OrderNoteDto> {
    const op: CollaborationOperation<{ body: string }> = {
      id: `local_${crypto.randomUUID()}`,
      actorId: this.transport.actorId,
      clock: 0,
      type: "note.create",
      payload: { body },
    };
    await this.transport.send(op);
    const res = await fetch("/api/admin/order-notes", {
      method: "POST",
      headers: { "content-type": "application/json" },
      body: JSON.stringify({ order_id: orderId, body }),
    });
    if (!res.ok) throw new Error(`add failed: ${res.status}`);
    return (await res.json()) as OrderNoteDto;
  }

  async update(note: OrderNoteDto, body: string, expectedVersion: number): Promise<OrderNoteDto> {
    await this.transport.send({
      id: note.note_id,
      actorId: "self",
      clock: note.clock,
      type: "note.update",
      payload: { body },
    });
    const res = await fetch("/api/admin/order-notes", {
      method: "PATCH",
      headers: { "content-type": "application/json" },
      body: JSON.stringify({ note_id: note.note_id, body, version: expectedVersion }),
    });
    if (res.status === 409) {
      const err = (await res.json()) as { current_version?: number };
      throw new ConflictError(note.note_id, err.current_version ?? 0);
    }
    if (!res.ok) throw new Error(`update failed: ${res.status}`);
    return (await res.json()) as OrderNoteDto;
  }
}