import { WebSocketServer, WebSocket, RawData } from "ws";
import type { YonexusServerConfig } from "./config.js";
import { safeErrorMessage } from "./logging.js";

export interface ClientConnection {
  readonly identifier: string | null;
  readonly ws: WebSocket;
  readonly connectedAt: number;
  isAuthenticated: boolean;
}

/**
 * Temporary connection tracking before authentication.
 * Connections remain in this state until successfully authenticated.
 */
interface TempConnection {
  readonly ws: WebSocket;
  readonly connectedAt: number;
  /** The identifier claimed during hello, if any */
  assignedIdentifier: string | null;
}

export interface ServerTransport {
  readonly isRunning: boolean;
  readonly connections: ReadonlyMap<string, ClientConnection>;
  start(): Promise<void>;
  stop(): Promise<void>;
  send(identifier: string, message: string): boolean;
  sendToConnection(connection: ClientConnection, message: string): boolean;
  broadcast(message: string): void;
  closeConnection(identifier: string, code?: number, reason?: string): boolean;
  /**
   * Promote a temp connection to authenticated status.
   * This implements the single-identifier-single-active-connection policy:
   * - If another authenticated connection exists for this identifier, it is closed
   * - The connection is moved from temp to authenticated registry
   */
  promoteToAuthenticated(identifier: string, ws: WebSocket): boolean;
  /**
   * Remove a temp connection without promoting it.
   * Called when authentication fails or connection closes before auth.
   */
  removeTempConnection(ws: WebSocket): void;
  /**
   * Assign an identifier to a temp connection during hello processing.
   * This does NOT register the connection as authenticated yet.
   */
  assignIdentifierToTemp(ws: WebSocket, identifier: string): void;
}

export type MessageHandler = (connection: ClientConnection, message: string) => void;
export type ConnectionHandler = (identifier: string | null, ws: WebSocket) => void;
export type DisconnectionHandler = (identifier: string | null, code: number, reason: Buffer) => void;

export interface ServerTransportOptions {
  config: YonexusServerConfig;
  onMessage: MessageHandler;
  onConnect?: ConnectionHandler;
  onDisconnect?: DisconnectionHandler;
}

export class YonexusServerTransport implements ServerTransport {
  private wss: WebSocketServer | null = null;
  private _connections = new Map<string, ClientConnection>();
  private tempConnections = new Map<WebSocket, TempConnection>();
  private options: ServerTransportOptions;
  private _isRunning = false;

  constructor(options: ServerTransportOptions) {
    this.options = options;
  }

  get isRunning(): boolean {
    return this._isRunning;
  }

  get connections(): ReadonlyMap<string, ClientConnection> {
    return this._connections;
  }

  async start(): Promise<void> {
    if (this._isRunning) {
      throw new Error("Server transport is already running");
    }

    const { listenHost, listenPort } = this.options.config;

    return new Promise((resolve, reject) => {
      this.wss = new WebSocketServer({
        host: listenHost,
        port: listenPort
      });

      this.wss.on("error", (error) => {
        if (!this._isRunning) {
          reject(error);
        }
      });

      this.wss.on("listening", () => {
        this._isRunning = true;
        resolve();
      });

      this.wss.on("connection", (ws, req) => {
        this.handleConnection(ws, req);
      });
    });
  }

  async stop(): Promise<void> {
    if (!this._isRunning || !this.wss) {
      return;
    }

    // Close all authenticated connections
    for (const conn of this._connections.values()) {
      conn.ws.close(1000, "Server shutting down");
    }
    this._connections.clear();

    // Close all temp connections
    for (const temp of this.tempConnections.values()) {
      temp.ws.close(1000, "Server shutting down");
    }
    this.tempConnections.clear();

    return new Promise((resolve) => {
      this.wss!.close(() => {
        this._isRunning = false;
        this.wss = null;
        resolve();
      });
    });
  }

  send(identifier: string, message: string): boolean {
    const conn = this._connections.get(identifier);
    if (!conn) {
      return false;
    }

    return this.sendToConnection(conn, message);
  }

  sendToConnection(connection: ClientConnection, message: string): boolean {
    const { ws } = connection;
    if (ws.readyState === WebSocket.OPEN) {
      ws.send(message);
      return true;
    }
    return false;
  }

  broadcast(message: string): void {
    for (const conn of this._connections.values()) {
      if (conn.isAuthenticated) {
        this.sendToConnection(conn, message);
      }
    }
  }

  closeConnection(identifier: string, code = 1000, reason = "Connection closed"): boolean {
    const conn = this._connections.get(identifier);
    if (!conn) {
      return false;
    }

    conn.ws.close(code, reason);
    this._connections.delete(identifier);
    return true;
  }

  promoteToAuthenticated(identifier: string, ws: WebSocket): boolean {
    // Verify the connection exists in temp connections
    const tempConn = this.tempConnections.get(ws);
    if (!tempConn) {
      return false;
    }

    // Check if already have an authenticated connection for this identifier
    // If so, close it (single-identifier-single-active-connection policy)
    const existingConn = this._connections.get(identifier);
    if (existingConn) {
      existingConn.ws.close(1008, "Connection replaced by new authenticated session");
      this._connections.delete(identifier);
    }

    // Remove from temp connections
    this.tempConnections.delete(ws);

    // Register the new authenticated connection
    const conn: ClientConnection = {
      identifier,
      ws,
      connectedAt: tempConn.connectedAt,
      isAuthenticated: true
    };

    this._connections.set(identifier, conn);
    return true;
  }

  removeTempConnection(ws: WebSocket): void {
    this.tempConnections.delete(ws);
  }

  assignIdentifierToTemp(ws: WebSocket, identifier: string): void {
    const tempConn = this.tempConnections.get(ws);
    if (tempConn) {
      tempConn.assignedIdentifier = identifier;
    }
  }

  private handleConnection(ws: WebSocket, _req: import("http").IncomingMessage): void {
    // Store as temp connection until authenticated
    this.tempConnections.set(ws, {
      ws,
      connectedAt: Math.floor(Date.now() / 1000),
      assignedIdentifier: null
    });

    const tempConn: ClientConnection = {
      identifier: null,
      ws,
      connectedAt: Math.floor(Date.now() / 1000),
      isAuthenticated: false
    };

    ws.on("message", (data: RawData) => {
      const message = data.toString("utf8");
      // Try to get identifier from temp connections first, then authenticated connections
      let identifier: string | null = null;
      const tempData = this.tempConnections.get(ws);
      if (tempData) {
        identifier = tempData.assignedIdentifier;
      }
      if (!identifier) {
        for (const [id, conn] of this._connections) {
          if (conn.ws === ws) {
            identifier = id;
            break;
          }
        }
      }

      const connection = identifier ? this._connections.get(identifier) ?? tempConn : tempConn;
      this.options.onMessage(connection, message);
    });

    ws.on("close", (code: number, reason: Buffer) => {
      this.tempConnections.delete(ws);

      // Find and remove from authenticated connections
      for (const [id, conn] of this._connections) {
        if (conn.ws === ws) {
          this._connections.delete(id);
          if (this.options.onDisconnect) {
            this.options.onDisconnect(id, code, reason);
          }
          return;
        }
      }

      if (this.options.onDisconnect) {
        this.options.onDisconnect(null, code, reason);
      }
    });

    ws.on("error", (error: Error) => {
      // Log error but let close handler clean up
      console.error("[Yonexus.Server] WebSocket error:", safeErrorMessage(error));
    });

    if (this.options.onConnect) {
      this.options.onConnect(null, ws);
    }
  }
}

export function createServerTransport(options: ServerTransportOptions): ServerTransport {
  return new YonexusServerTransport(options);
}