import { assertRealtimeRoomName, createRealtimeMessage, type RealtimeMessage } from "./messages.ts";

export interface SequencedRealtimeMessage<T = unknown> {
  sequence: number;
  message: RealtimeMessage<T>;
}
export interface RealtimeHistorySnapshot {
  rooms: number;
  messages: number;
  acknowledgements: number;
  oldestSequence?: number;
  latestSequence?: number;
}
export interface RealtimeHistoryOptions {
  limitPerRoom?: number;
  maxClients?: number;
}
export interface RealtimeHistory {
  publish<T>(room: string, message: RealtimeMessage<T>): SequencedRealtimeMessage<T>;
  replay(room: string, afterSequence?: number, limit?: number): SequencedRealtimeMessage[];
  acknowledge(room: string, clientId: string, sequence: number): void;
  acknowledged(room: string, clientId: string): number;
  resume(room: string, clientId: string, limit?: number): SequencedRealtimeMessage[];
  snapshot(): RealtimeHistorySnapshot;
  clear(room?: string): void;
}

export function createRealtimeHistory(options: RealtimeHistoryOptions = {}): RealtimeHistory {
  const limitPerRoom = options.limitPerRoom ?? 100;
  const maxClients = options.maxClients ?? 10_000;
  if (!Number.isInteger(limitPerRoom) || limitPerRoom < 1)
    throw new RangeError("realtime history limitPerRoom must be positive");
  if (!Number.isInteger(maxClients) || maxClients < 1)
    throw new RangeError("realtime history maxClients must be positive");
  const rooms = new Map<string, SequencedRealtimeMessage[]>();
  const acknowledgements = new Map<string, number>();
  let sequence = 0;
  const publishMonitor = () => {
    const values = [...rooms.values()].flat();
    (
      globalThis as typeof globalThis & { __wrnexusRealtimeMonitor?: RealtimeHistorySnapshot }
    ).__wrnexusRealtimeMonitor = {
      rooms: rooms.size,
      messages: values.length,
      acknowledgements: acknowledgements.size,
      oldestSequence: values.length
        ? Math.min(...values.map((entry) => entry.sequence))
        : undefined,
      latestSequence: values.length
        ? Math.max(...values.map((entry) => entry.sequence))
        : undefined,
    };
  };
  const ackKey = (room: string, clientId: string) => `${room}\0${clientId}`;
  return {
    publish(roomName, message) {
      const room = assertRealtimeRoomName(roomName);
      if (message.room && message.room !== room)
        throw new Error("WRN-REALTIME-HISTORY-ROOM: message room mismatch.");
      const entry = { sequence: ++sequence, message: structuredClone(message) };
      const values = rooms.get(room) ?? [];
      values.push(entry);
      if (values.length > limitPerRoom) values.splice(0, values.length - limitPerRoom);
      rooms.set(room, values);
      publishMonitor();
      return structuredClone(entry);
    },
    replay(roomName, afterSequence = 0, limit = limitPerRoom) {
      const room = assertRealtimeRoomName(roomName);
      if (!Number.isInteger(afterSequence) || afterSequence < 0)
        throw new RangeError("realtime replay sequence must be non-negative");
      if (!Number.isInteger(limit) || limit < 1 || limit > limitPerRoom)
        throw new RangeError(`realtime replay limit must be between 1 and ${limitPerRoom}`);
      return (rooms.get(room) ?? [])
        .filter((entry) => entry.sequence > afterSequence)
        .slice(0, limit)
        .map((entry) => structuredClone(entry));
    },
    acknowledge(roomName, clientId, value) {
      const room = assertRealtimeRoomName(roomName);
      if (!clientId.trim() || clientId.length > 256)
        throw new TypeError("invalid realtime client id");
      if (!Number.isInteger(value) || value < 0 || value > sequence)
        throw new RangeError("invalid realtime acknowledgement sequence");
      const key = ackKey(room, clientId);
      if (!acknowledgements.has(key) && acknowledgements.size >= maxClients)
        throw new Error("WRN-REALTIME-ACK-CAPACITY");
      acknowledgements.set(key, Math.max(acknowledgements.get(key) ?? 0, value));
      publishMonitor();
    },
    acknowledged(roomName, clientId) {
      return acknowledgements.get(ackKey(assertRealtimeRoomName(roomName), clientId)) ?? 0;
    },
    resume(roomName, clientId, limit) {
      const room = assertRealtimeRoomName(roomName);
      return this.replay(room, this.acknowledged(room, clientId), limit);
    },
    snapshot() {
      const values = [...rooms.values()].flat();
      return {
        rooms: rooms.size,
        messages: values.length,
        acknowledgements: acknowledgements.size,
        oldestSequence: values.length
          ? Math.min(...values.map((entry) => entry.sequence))
          : undefined,
        latestSequence: values.length
          ? Math.max(...values.map((entry) => entry.sequence))
          : undefined,
      };
    },
    clear(roomName) {
      if (!roomName) {
        rooms.clear();
        acknowledgements.clear();
        publishMonitor();
        return;
      }
      const room = assertRealtimeRoomName(roomName);
      rooms.delete(room);
      for (const key of acknowledgements.keys())
        if (key.startsWith(`${room}\0`)) acknowledgements.delete(key);
      publishMonitor();
    },
  };
}

export function createAcknowledgement(
  room: string,
  sequence: number,
  clientId: string,
): RealtimeMessage<{ sequence: number; clientId: string }> {
  return createRealtimeMessage({ type: "ack", room, data: { sequence, clientId } });
}

export function realtimeSseResponse(
  stream: ReadableStream<SequencedRealtimeMessage>,
  signal?: AbortSignal,
): Response {
  const encoder = new TextEncoder();
  const output = new TransformStream<SequencedRealtimeMessage, Uint8Array>({
    transform(entry, controller) {
      controller.enqueue(
        encoder.encode(
          `id: ${entry.sequence}\nevent: ${entry.message.type}\ndata: ${JSON.stringify(entry.message)}\n\n`,
        ),
      );
    },
  });
  signal?.addEventListener("abort", () => void output.writable.abort(signal.reason), {
    once: true,
  });
  return new Response(stream.pipeThrough(output), {
    headers: {
      "content-type": "text/event-stream; charset=utf-8",
      "cache-control": "no-cache, no-transform",
      connection: "keep-alive",
    },
  });
}