// Client WebSocket multiplexé — UNE seule connexion pour toute l'app.
// Handshake hello/hello_ok, reconnexion avec backoff (ré-attache des terminaux
// ouverts + re-sub), corrélation FIFO des 'attached', flow control par ACK
// (cumul d'octets traités PAR CANAL, remis à zéro à chaque RESYNC).
import { ref, type Ref } from 'vue';
import {
  BINARY_FRAME,
  FLOW,
  PROTOCOL_VERSION,
  decodeBinaryFrame,
  type ClientMessage,
  type ServerMessage,
} from '@arboretum/shared';

export type WsStatus = 'idle' | 'connecting' | 'open' | 'reconnecting';

export type DetachReason = 'client' | 'session_exit' | 'replaced';

/** Interface minimale attendue côté terminal (implémentée par xterm). */
export interface TerminalSink {
  /** le callback est invoqué quand xterm a réellement traité le chunk (base du flow control) */
  write(data: Uint8Array, callback?: () => void): void;
  /** reset complet avant le replay d'une frame RESYNC */
  reset(): void;
  onDetached(reason: DetachReason): void;
  onControlChanged(controlling: boolean): void;
}

export type SessionEvent = Extract<ServerMessage, { type: 'session_update' | 'session_exit' }>;

export interface AttachOptions {
  sessionId: string;
  mode: 'interactive' | 'observer';
  cols: number;
  rows: number;
  sink: TerminalSink;
}

const BACKOFF_MIN_MS = 500;
const BACKOFF_MAX_MS = 10_000;

export class Attachment {
  /** canal courant — réassigné à chaque reconnexion, -1 tant que non attaché */
  channel = -1;
  controlling = false;
  closed = false;
  cols: number;
  rows: number;
  /** époque de resync : invalide les callbacks d'écritures encore en vol après un reset */
  epoch = 0;
  /** octets de payload réellement traités par le terminal depuis le dernier resync */
  processedBytes = 0;
  /** dernier cumul envoyé en ack (repart à 0 à chaque resync, comme côté serveur) */
  lastAckBytes = 0;
  /** ACK traînant : garantit l'envoi du reliquat même quand le flux s'arrête (anti-deadlock) */
  trailingAckTimer: ReturnType<typeof setTimeout> | null = null;
  /** résolution du premier 'attached' de ce canal (corrélation FIFO) */
  pending: { resolve: (a: Attachment) => void; reject: (err: Error) => void } | null = null;

  constructor(
    private readonly client: WsClient,
    readonly sessionId: string,
    readonly mode: 'interactive' | 'observer',
    readonly sink: TerminalSink,
    cols: number,
    rows: number,
  ) {
    this.cols = cols;
    this.rows = rows;
  }

  sendStdin(data: string): void {
    if (this.closed || this.channel < 0) return;
    this.client.sendControl({ type: 'stdin', channel: this.channel, data });
  }

  /** mémorise toujours la taille (réutilisée à la ré-attache) ; n'envoie que si controlling */
  resize(cols: number, rows: number): void {
    this.cols = cols;
    this.rows = rows;
    if (this.closed || this.channel < 0 || !this.controlling) return;
    this.client.sendControl({ type: 'resize', channel: this.channel, cols, rows });
  }

  detach(): void {
    if (this.closed) return;
    this.closed = true;
    this.pending = null;
    this.client.releaseAttachment(this);
  }
}

export class WsClient {
  readonly status: Ref<WsStatus> = ref('idle');

  private socket: WebSocket | null = null;
  private ready = false;
  private stopped = true;
  private backoffMs = BACKOFF_MIN_MS;
  private reconnectTimer: ReturnType<typeof setTimeout> | null = null;
  /** terminaux ouverts, ré-attachés à chaque reconnexion (ordre d'insertion = ordre FIFO) */
  private readonly attachments = new Set<Attachment>();
  private readonly byChannel = new Map<number, Attachment>();
  /** FIFO des attaches en attente : le serveur répond aux 'attach' dans l'ordre */
  private awaitingAttached: Attachment[] = [];
  private readonly sessionListeners = new Set<(e: SessionEvent) => void>();

  connect(): void {
    this.stopped = false;
    if (this.socket || this.reconnectTimer) return;
    if (this.status.value === 'idle') this.status.value = 'connecting';
    this.openSocket();
  }

  disconnect(): void {
    this.stopped = true;
    this.clearReconnectTimer();
    const socket = this.socket;
    this.socket = null;
    this.ready = false;
    this.status.value = 'idle';
    for (const att of this.attachments) {
      att.closed = true;
      att.pending?.reject(new Error('disconnected'));
      att.pending = null;
      att.sink.onDetached('client');
    }
    this.attachments.clear();
    this.byChannel.clear();
    this.awaitingAttached = [];
    socket?.close();
  }

  /** résout sur le prochain 'attached' corrélé ; rejette si la session est introuvable/terminée */
  attach(opts: AttachOptions): Promise<Attachment> {
    const att = new Attachment(this, opts.sessionId, opts.mode, opts.sink, opts.cols, opts.rows);
    const promise = new Promise<Attachment>((resolve, reject) => {
      att.pending = { resolve, reject };
    });
    this.attachments.add(att);
    this.connect();
    if (this.ready) this.sendAttach(att);
    return promise;
  }

  subscribeSessions(listener: (e: SessionEvent) => void): () => void {
    this.sessionListeners.add(listener);
    this.connect();
    if (this.sessionListeners.size === 1) this.sendControl({ type: 'sub', topics: ['sessions'] });
    return () => {
      this.sessionListeners.delete(listener);
      if (this.sessionListeners.size === 0) this.sendControl({ type: 'sub', topics: [] });
    };
  }

  sendControl(msg: ClientMessage): void {
    if (!this.ready || this.socket?.readyState !== WebSocket.OPEN) return;
    this.socket.send(JSON.stringify(msg));
  }

  /** détache côté serveur et oublie l'attache (appelé par Attachment.detach) */
  releaseAttachment(att: Attachment): void {
    this.attachments.delete(att);
    if (att.channel >= 0) {
      this.byChannel.delete(att.channel);
      this.sendControl({ type: 'detach', channel: att.channel });
      att.channel = -1;
    }
    // si l'attache attend encore son 'attached', elle reste dans la FIFO pour
    // préserver la corrélation : closed=true la fera détacher à la réception
  }

  // ---- interne ----

  private openSocket(): void {
    const socket = new WebSocket(`${location.origin.replace(/^http/, 'ws')}/ws`);
    socket.binaryType = 'arraybuffer';
    this.socket = socket;
    socket.onopen = () => {
      const hello: ClientMessage = { type: 'hello', protocol: PROTOCOL_VERSION };
      socket.send(JSON.stringify(hello));
    };
    socket.onmessage = (ev: MessageEvent) => this.handleMessage(ev);
    socket.onclose = () => this.handleClose(socket);
    socket.onerror = () => {
      // onclose suit systématiquement : la reconnexion se joue là-bas
    };
  }

  private handleClose(socket: WebSocket): void {
    if (this.socket !== socket) return;
    this.socket = null;
    this.ready = false;
    this.byChannel.clear();
    this.awaitingAttached = [];
    for (const att of this.attachments) {
      att.channel = -1;
      att.epoch += 1;
    }
    if (this.stopped) {
      this.status.value = 'idle';
      return;
    }
    this.status.value = 'reconnecting';
    this.scheduleReconnect();
  }

  private scheduleReconnect(): void {
    this.clearReconnectTimer();
    this.reconnectTimer = setTimeout(() => {
      this.reconnectTimer = null;
      if (!this.stopped) this.openSocket();
    }, this.backoffMs);
    this.backoffMs = Math.min(this.backoffMs * 2, BACKOFF_MAX_MS);
  }

  private clearReconnectTimer(): void {
    if (this.reconnectTimer !== null) {
      clearTimeout(this.reconnectTimer);
      this.reconnectTimer = null;
    }
  }

  private sendAttach(att: Attachment): void {
    this.awaitingAttached.push(att);
    this.sendControl({ type: 'attach', sessionId: att.sessionId, mode: att.mode, cols: att.cols, rows: att.rows });
  }

  private handleMessage(ev: MessageEvent): void {
    if (ev.data instanceof ArrayBuffer) {
      this.handleBinary(new Uint8Array(ev.data));
      return;
    }
    let msg: ServerMessage;
    try {
      msg = JSON.parse(String(ev.data)) as ServerMessage;
    } catch {
      return;
    }
    this.handleServerMessage(msg);
  }

  private handleBinary(data: Uint8Array): void {
    if (data.byteLength < BINARY_FRAME.HEADER_BYTES) return;
    const frame = decodeBinaryFrame(data);
    const att = this.byChannel.get(frame.channel);
    if (!att || att.closed) return;

    if (frame.type === BINARY_FRAME.RESYNC) {
      // le serveur repart de sentBytes=0 après un resync : reset terminal, replay
      // du ring, et compteurs d'octets remis à zéro (le payload du replay ne compte pas)
      att.epoch += 1;
      att.processedBytes = 0;
      att.lastAckBytes = 0;
      att.sink.reset();
      if (frame.payload.byteLength > 0) att.sink.write(frame.payload);
      return;
    }
    if (frame.type !== BINARY_FRAME.OUTPUT) return;

    const epoch = att.epoch;
    const length = frame.payload.byteLength;
    att.sink.write(frame.payload, () => {
      // compté seulement si aucun resync/reconnexion n'est passé entre temps
      if (att.closed || att.epoch !== epoch || att.channel < 0) return;
      att.processedBytes += length;
      if (att.processedBytes - att.lastAckBytes >= FLOW.ACK_EVERY_BYTES) {
        att.lastAckBytes = att.processedBytes;
        this.sendControl({ type: 'ack', channel: att.channel, bytes: att.processedBytes });
      }
      // ACK traînant débouncé : si le flux s'arrête avec un reliquat non-ACKé,
      // le serveur ne doit jamais rester en pause faute d'ACK suivant.
      if (att.trailingAckTimer) clearTimeout(att.trailingAckTimer);
      att.trailingAckTimer = setTimeout(() => {
        att.trailingAckTimer = null;
        if (att.closed || att.epoch !== epoch || att.channel < 0) return;
        if (att.processedBytes > att.lastAckBytes) {
          att.lastAckBytes = att.processedBytes;
          this.sendControl({ type: 'ack', channel: att.channel, bytes: att.processedBytes });
        }
      }, 200);
    });
  }

  private handleServerMessage(msg: ServerMessage): void {
    switch (msg.type) {
      case 'hello_ok': {
        this.ready = true;
        this.backoffMs = BACKOFF_MIN_MS;
        this.status.value = 'open';
        if (this.sessionListeners.size > 0) this.sendControl({ type: 'sub', topics: ['sessions'] });
        // ré-attache des terminaux encore ouverts (nouveaux canaux côté serveur)
        for (const att of this.attachments) {
          if (!att.closed) this.sendAttach(att);
        }
        return;
      }
      case 'attached': {
        const att = this.awaitingAttached.shift();
        if (!att) return;
        if (att.closed) {
          // détaché pendant l'attente : on libère le canal côté serveur
          this.sendControl({ type: 'detach', channel: msg.channel });
          return;
        }
        const wasControlling = att.controlling;
        att.channel = msg.channel;
        att.controlling = msg.controlling;
        this.byChannel.set(msg.channel, att);
        if (att.pending) {
          att.pending.resolve(att);
          att.pending = null;
        } else if (wasControlling !== msg.controlling) {
          // ré-attache après reconnexion : le statut controlling peut avoir changé
          att.sink.onControlChanged(msg.controlling);
        }
        return;
      }
      case 'detached': {
        const att = this.byChannel.get(msg.channel);
        if (!att) return;
        this.byChannel.delete(msg.channel);
        att.channel = -1;
        if (msg.reason === 'client') return;
        att.closed = true;
        this.attachments.delete(att);
        att.sink.onDetached(msg.reason);
        return;
      }
      case 'control_changed': {
        const att = this.byChannel.get(msg.channel);
        if (!att || att.closed) return;
        att.controlling = msg.controlling;
        att.sink.onControlChanged(msg.controlling);
        return;
      }
      case 'session_update':
      case 'session_exit': {
        for (const cb of this.sessionListeners) cb(msg);
        return;
      }
      case 'error': {
        if (msg.channel !== undefined) {
          console.warn(`[ws] channel ${msg.channel}: ${msg.code} — ${msg.message}`);
          return;
        }
        // un échec d'attach est la seule erreur sans canal corrélable à une requête
        if ((msg.code === 'NOT_FOUND' || msg.code === 'SESSION_EXITED') && this.awaitingAttached.length > 0) {
          const att = this.awaitingAttached.shift();
          if (!att) return;
          this.attachments.delete(att);
          if (att.pending) {
            att.pending.reject(new Error(msg.code));
            att.pending = null;
          } else if (!att.closed) {
            att.closed = true;
            att.sink.onDetached('session_exit');
          }
          return;
        }
        console.warn(`[ws] ${msg.code} — ${msg.message}`);
        return;
      }
      case 'pong':
        return;
    }
  }
}

export const wsClient = new WsClient();