// SDK Client for Auth-Yes Zero Trust Identity Provider
// Designed to be imported by subsidiary applications to validate stateful session tokens.

import { Redis } from "npm:ioredis";
import { createClient } from "npm:@connectrpc/connect@^1.4.0";
import { createConnectTransport } from "npm:@connectrpc/connect-node@^1.4.0";
import { AuthService } from "./gen/auth_connect.ts";

/**
 * Supported event types for the Auth SDK.
 */
export type AuthSdkEvent = "invalidate";

/**
 * Handler type for invalidation events.
 */
export type InvalidationHandler = (token: string) => void | Promise<void>;

/**
 * Configuration options for the Auth SDK.
 */
export interface AuthSdkConfig {
  /**
   * The internal network URL of the Auth API Gateway.
   * e.g., 'http://auth-api.internal:8000'
   */
  authApiUrl: string;
  /**
   * The Valkey URL for RESP3 Client-Side Caching (optional).
   * e.g., 'redis://auth-valkey:6379'
   */
  valkeyUrl?: string;
  /**
   * Optional custom transport if deploying in environments (like browser)
   * where connect-node is unavailable.
   */
  customTransport?: any;
  /**
   * The mTLS certificate.
   */
  tlsCert?: string;
  /**
   * The mTLS private key.
   */
  tlsKey?: string;
  /**
   * The mTLS CA certificate.
   */
  tlsCa?: string;
  /**
   * Network timeout for ConnectRPC calls in milliseconds (default: 5000ms).
   */
  timeoutMs?: number;
}

/**
 * The validated session data returned by the Auth API.
 */
export interface SessionData {
  valid: boolean;
  uuid?: string;
  scopes?: string[];
  error?: string;
}

export class AuthSdk {
  private config: AuthSdkConfig;
  private l1Cache: Map<string, SessionData>;
  private valkeyClient: Redis | null = null;
  private grpcClient: any;
  private listeners: Map<string, Set<InvalidationHandler>> = new Map();

  constructor(config: AuthSdkConfig) {
    this.config = config;
    this.l1Cache = new Map();

    if (this.config.valkeyUrl) {
      this.initValkeyClient();
    }

    const nodeOptions: Record<string, any> = { rejectUnauthorized: false };
    if (this.config.tlsCert && this.config.tlsKey && this.config.tlsCa) {
      nodeOptions.rejectUnauthorized = true;
      nodeOptions.cert = this.config.tlsCert;
      nodeOptions.key = this.config.tlsKey;
      nodeOptions.ca = this.config.tlsCa;
    }

    const transport = this.config.customTransport || createConnectTransport({
      baseUrl: this.config.authApiUrl,
      httpVersion: "2",
      nodeOptions: nodeOptions,
    });

    this.grpcClient = createClient(AuthService, transport);
  }

  /**
   * Registers a callback to be invoked when a specific event occurs.
   *
   * @param event The event name (e.g., "invalidate").
   * @param handler The callback function.
   */
  on(event: AuthSdkEvent, handler: InvalidationHandler): void {
    let eventListeners = this.listeners.get(event);
    if (!eventListeners) {
      eventListeners = new Set();
      this.listeners.set(event, eventListeners);
    }
    eventListeners.add(handler);
  }

  /**
   * Unregisters a previously registered callback.
   *
   * @param event The event name (e.g., "invalidate").
   * @param handler The callback function to remove.
   */
  off(event: AuthSdkEvent, handler: InvalidationHandler): void {
    const eventListeners = this.listeners.get(event);
    if (eventListeners) {
      eventListeners.delete(handler);
      if (eventListeners.size === 0) {
        this.listeners.delete(event);
      }
    }
  }

  /**
   * Internal method to emit an event safely to all registered listeners.
   */
  private emit(event: AuthSdkEvent, token: string): void {
    const eventListeners = this.listeners.get(event);
    if (eventListeners) {
      for (const handler of eventListeners) {
        try {
          const result = handler(token);
          if (result instanceof Promise) {
            result.catch((err) => {
              console.error("[AuthSdk] Error in 'invalidate' listener:", err);
            });
          }
        } catch (err) {
          console.error("[AuthSdk] Error in 'invalidate' listener:", err);
        }
      }
    }
  }

  /**
   * Internal handler for RESP3 push invalidation messages.
   * Exposed internally/to tests via the Valkey event listener.
   */
  _handleValkeyPush(msg: unknown): void {
    if (
      Array.isArray(msg) && msg.length >= 2 && msg[0] === "invalidate"
    ) {
      const keysToInvalidate = msg[1];
      if (Array.isArray(keysToInvalidate)) {
        for (const key of keysToInvalidate) {
          // SIDE EFFECT: Delete the invalidated key from the local Map
          this.l1Cache.delete(key);
          // Emit invalidate event for real-time consumers
          this.emit("invalidate", key);
        }
      }
    }
  }

  private initValkeyClient() {
    this.valkeyClient = new Redis(this.config.valkeyUrl!, {
      enableOfflineQueue: false,
    });

    this.valkeyClient.on("ready", async () => {
      // Negotiate RESP3 and enable client tracking
      try {
        await this.valkeyClient!.hello(3);
        // Enable tracking in BCAST (broadcast) mode because this client
        // never actually issues GET commands to trigger standard tracking
        await this.valkeyClient!.client("TRACKING", "ON", "BCAST");
      } catch (e) {
        console.error("Failed to enable RESP3 client tracking:", e);
      }
    });

    // Listen for RESP3 push invalidation messages
    this.valkeyClient.on("push", (msg: unknown) => this._handleValkeyPush(msg));

    this.valkeyClient.on("error", (err: unknown) => {
      console.error("Valkey SDK Client error:", err);
      console.warn(
        "[AuthSdk] Valkey connection lost. Clearing L1 cache to prevent stale sessions.",
      );
      this.l1Cache.clear();
    });

    this.valkeyClient.on("close", () => {
      console.warn(
        "[AuthSdk] Valkey connection lost. Clearing L1 cache to prevent stale sessions.",
      );
      this.l1Cache.clear();
    });

    this.valkeyClient.on("end", () => {
      console.warn(
        "[AuthSdk] Valkey connection lost. Clearing L1 cache to prevent stale sessions.",
      );
      this.l1Cache.clear();
    });
  }

  /**
   * Validates an opaque session token against the Auth API.
   * This is a fast-path operation that leverages the central Valkey cache.
   *
   * @param token The opaque session token (e.g., extracted from a cookie).
   * @returns The validated session data containing the UUID and scopes.
   */
  async validateSession(
    token: string,
    options?: { signal?: AbortSignal },
  ): Promise<SessionData> {
    // Check L1 cache first
    const cachedSession = this.l1Cache.get(token);
    if (cachedSession) {
      return cachedSession;
    }

    try {
      const timeout = this.config.timeoutMs || 5000;
      const signal = options?.signal || AbortSignal.timeout(timeout);
      const response = await this.grpcClient.validateSession(
        { token },
        { signal },
      );

      const sessionData: SessionData = {
        valid: response.valid,
        uuid: response.uuid,
        scopes: response.scopes || [],
        error: response.error,
      };

      // Only populate L1 cache if Valkey integration is enabled for invalidations
      if (sessionData.valid && this.config.valkeyUrl) {
        this.l1Cache.set(token, sessionData);
      }

      return sessionData;
    } catch (error) {
      // Typically network errors or internal DNS resolution failures
      return {
        valid: false,
        error: error instanceof Error ? error.message : "Unknown error",
      };
    }
  }

  /**
   * Middleware for web frameworks (e.g., Oak, Hono) to intercept and validate requests.
   * Developers should wrap this around protected routes.
   *
   * @param token The extracted session token.
   * @throws Error if the token is invalid or missing.
   * @returns The user's UUID.
   */
  async requireAuth(token: string | null | undefined): Promise<string> {
    if (!token) {
      throw new Error("Unauthorized: Missing session token.");
    }

    const session = await this.validateSession(token);
    if (!session.valid || !session.uuid) {
      throw new Error(`Unauthorized: ${session.error || "Invalid session."}`);
    }

    return session.uuid;
  }
}

/**
 * Creates a new instance of the Auth SDK.
 */
export function createAuthSdk(config: AuthSdkConfig): AuthSdk {
  return new AuthSdk(config);
}