/**
 * WebSocket client for connecting to agor-relay instances.
 *
 * Features:
 * - Token-based auth handshake (Bearer header)
 * - Exponential backoff reconnection (1s–30s cap)
 * - TCP probe before full WS upgrade on reconnect
 * - Per-connection command routing
 * - Event forwarding to webview via callback
 */

import { randomUUID } from "crypto";
import { Socket } from "net";

// ── Types ──────────────────────────────────────────────────────────────────

export type ConnectionStatus = "connecting" | "connected" | "disconnected" | "error";

export interface RelayCommand {
  id: string;
  type: string;
  payload: Record<string, unknown>;
}

export interface RelayEvent {
  type: string;
  sessionId?: string;
  machineId?: string;
  payload?: unknown;
}

export type EventCallback = (machineId: string, event: RelayEvent) => void;
export type StatusCallback = (machineId: string, status: ConnectionStatus, error?: string) => void;

interface MachineConnection {
  machineId: string;
  label: string;
  url: string;
  token: string;
  status: ConnectionStatus;
  latencyMs: number | null;
  ws: WebSocket | null;
  heartbeatTimer: ReturnType<typeof setInterval> | null;
  reconnectTimer: ReturnType<typeof setTimeout> | null;
  cancelled: boolean;
  lastPingSent: number;
}

// ── Relay Client ───────────────────────────────────────────────────────────

export class RelayClient {
  private machines = new Map<string, MachineConnection>();
  private eventListeners: EventCallback[] = [];
  private statusListeners: StatusCallback[] = [];

  /** Register an event listener for relay events from any machine. */
  onEvent(cb: EventCallback): void {
    this.eventListeners.push(cb);
  }

  /** Register a listener for connection status changes. */
  onStatus(cb: StatusCallback): void {
    this.statusListeners.push(cb);
  }

  /**
   * Connect to an agor-relay instance.
   * Fix #4 (Codex audit): Returns { ok, machineId, error } instead of always
   * returning machineId even on failure.
   */
  async connect(url: string, token: string, label?: string): Promise<{ ok: boolean; machineId?: string; error?: string }> {
    const machineId = randomUUID();
    const machine: MachineConnection = {
      machineId,
      label: label ?? url,
      url,
      token,
      status: "connecting",
      latencyMs: null,
      ws: null,
      heartbeatTimer: null,
      reconnectTimer: null,
      cancelled: false,
      lastPingSent: 0,
    };
    this.machines.set(machineId, machine);
    this.emitStatus(machineId, "connecting");

    try {
      await this.openWebSocket(machine);
      return { ok: true, machineId };
    } catch (err) {
      const msg = err instanceof Error ? err.message : String(err);
      machine.status = "error";
      this.emitStatus(machineId, "error", msg);
      this.scheduleReconnect(machine);
      return { ok: false, machineId, error: msg };
    }
  }

  /** Disconnect from a relay and stop reconnection attempts. */
  disconnect(machineId: string): void {
    const machine = this.machines.get(machineId);
    if (!machine) return;

    machine.cancelled = true;
    this.cleanupConnection(machine);
    machine.status = "disconnected";
    this.emitStatus(machineId, "disconnected");
  }

  /** Remove a machine entirely from tracking. */
  removeMachine(machineId: string): void {
    this.disconnect(machineId);
    this.machines.delete(machineId);
  }

  /** Send a command to a connected relay. */
  sendCommand(machineId: string, type: string, payload: Record<string, unknown>): void {
    const machine = this.machines.get(machineId);
    if (!machine?.ws || machine.status !== "connected") {
      throw new Error(`Machine ${machineId} not connected`);
    }

    const cmd: RelayCommand = {
      id: randomUUID(),
      type,
      payload,
    };
    machine.ws.send(JSON.stringify(cmd));
  }

  /** Get the status of a specific machine. */
  getStatus(machineId: string): { status: ConnectionStatus; latencyMs: number | null } | null {
    const machine = this.machines.get(machineId);
    if (!machine) return null;
    return { status: machine.status, latencyMs: machine.latencyMs };
  }

  /** List all tracked machines. */
  listMachines(): Array<{
    machineId: string;
    label: string;
    url: string;
    status: ConnectionStatus;
    latencyMs: number | null;
  }> {
    return Array.from(this.machines.values()).map((m) => ({
      machineId: m.machineId,
      label: m.label,
      url: m.url,
      status: m.status,
      latencyMs: m.latencyMs,
    }));
  }

  // ── Internal ─────────────────────────────────────────────────────────────

  private async openWebSocket(machine: MachineConnection): Promise<void> {
    return new Promise<void>((resolve, reject) => {
      const ws = new WebSocket(machine.url, {
        headers: {
          Authorization: `Bearer ${machine.token}`,
        },
      } as unknown as string[]);

      const timeout = setTimeout(() => {
        ws.close();
        reject(new Error("Connection timeout (10s)"));
      }, 10_000);

      ws.addEventListener("open", () => {
        clearTimeout(timeout);
        machine.ws = ws;
        machine.status = "connected";
        machine.cancelled = false;
        this.emitStatus(machine.machineId, "connected");
        this.startHeartbeat(machine);
        resolve();
      });

      ws.addEventListener("message", (ev) => {
        this.handleMessage(machine, String(ev.data));
      });

      ws.addEventListener("close", () => {
        clearTimeout(timeout);
        if (machine.status === "connected") {
          this.cleanupConnection(machine);
          machine.status = "disconnected";
          this.emitStatus(machine.machineId, "disconnected");
          if (!machine.cancelled) {
            this.scheduleReconnect(machine);
          }
        }
      });

      ws.addEventListener("error", (ev) => {
        clearTimeout(timeout);
        const errMsg = "WebSocket error";
        if (machine.status !== "connected") {
          reject(new Error(errMsg));
        } else {
          this.cleanupConnection(machine);
          machine.status = "error";
          this.emitStatus(machine.machineId, "error", errMsg);
          if (!machine.cancelled) {
            this.scheduleReconnect(machine);
          }
        }
      });
    });
  }

  private handleMessage(machine: MachineConnection, data: string): void {
    let event: RelayEvent;
    try {
      event = JSON.parse(data) as RelayEvent;
    } catch {
      console.error(`[relay] Invalid JSON from ${machine.machineId}`);
      return;
    }

    // Handle pong for latency measurement
    if (event.type === "pong") {
      if (machine.lastPingSent > 0) {
        machine.latencyMs = Date.now() - machine.lastPingSent;
      }
      return;
    }

    // Forward all other events
    event.machineId = machine.machineId;
    for (const cb of this.eventListeners) {
      try {
        cb(machine.machineId, event);
      } catch (err) {
        console.error("[relay] Event listener error:", err);
      }
    }
  }

  private startHeartbeat(machine: MachineConnection): void {
    this.stopHeartbeat(machine);
    machine.heartbeatTimer = setInterval(() => {
      if (machine.ws?.readyState === WebSocket.OPEN) {
        machine.lastPingSent = Date.now();
        machine.ws.send(JSON.stringify({ id: "", type: "ping", payload: {} }));
      }
    }, 15_000);
  }

  private stopHeartbeat(machine: MachineConnection): void {
    if (machine.heartbeatTimer) {
      clearInterval(machine.heartbeatTimer);
      machine.heartbeatTimer = null;
    }
  }

  private cleanupConnection(machine: MachineConnection): void {
    this.stopHeartbeat(machine);
    if (machine.reconnectTimer) {
      clearTimeout(machine.reconnectTimer);
      machine.reconnectTimer = null;
    }
    if (machine.ws) {
      try { machine.ws.close(); } catch { /* ignore */ }
      machine.ws = null;
    }
  }

  private scheduleReconnect(machine: MachineConnection): void {
    let delay = 1_000;
    const maxDelay = 30_000;

    const attempt = async () => {
      if (machine.cancelled || !this.machines.has(machine.machineId)) return;

      machine.status = "connecting";
      this.emitStatus(machine.machineId, "connecting");

      // TCP probe first — avoids full WS overhead if host unreachable
      const probeOk = await this.tcpProbe(machine.url);
      if (!probeOk) {
        delay = Math.min(delay * 2, maxDelay);
        if (!machine.cancelled) {
          machine.reconnectTimer = setTimeout(attempt, delay);
        }
        return;
      }

      try {
        await this.openWebSocket(machine);
        // Success — reset
      } catch {
        delay = Math.min(delay * 2, maxDelay);
        if (!machine.cancelled) {
          machine.reconnectTimer = setTimeout(attempt, delay);
        }
      }
    };

    machine.reconnectTimer = setTimeout(attempt, delay);
  }

  /**
   * TCP-only probe to check if the relay host is reachable.
   * Fix #15 (Codex audit): Uses URL() to correctly parse IPv6, ports, etc.
   */
  private tcpProbe(wsUrl: string): Promise<boolean> {
    return new Promise((resolve) => {
      let hostname: string;
      let port: number;
      try {
        // Convert ws/wss to http/https so URL() can parse it
        const httpUrl = wsUrl.replace(/^ws(s)?:\/\//, "http$1://");
        const parsed = new URL(httpUrl);
        hostname = parsed.hostname; // strips IPv6 brackets automatically
        port = parsed.port ? parseInt(parsed.port, 10) : 9750;
      } catch {
        resolve(false);
        return;
      }

      const socket = new Socket();
      const timer = setTimeout(() => { socket.destroy(); resolve(false); }, 5_000);

      socket.connect(port, hostname, () => {
        clearTimeout(timer);
        socket.destroy();
        resolve(true);
      });

      socket.on("error", () => {
        clearTimeout(timer);
        socket.destroy();
        resolve(false);
      });
    });
  }

  private emitStatus(machineId: string, status: ConnectionStatus, error?: string): void {
    for (const cb of this.statusListeners) {
      try {
        cb(machineId, status, error);
      } catch (err) {
        console.error("[relay] Status listener error:", err);
      }
    }
  }
}