/**
 * @fileoverview API server factory module.
 * Exports a function to create and start the API server.
 * This allows the server to be started in-process from the main application.
 * 
 * Routes are organized into modular files in the ./routes directory.
 * Each route module handles its own validation, business logic, and responses.
 */

import { serve } from "bun";
import { logger } from "@shared/lib/logger";
import { handleRequest } from "./routes";
import { getFullDashboardStats } from "./routes/stats.helper";

export interface WebServerConfig {
    port?: number;
    hostname?: string;
}

export interface WebServerInstance {
    server: ReturnType<typeof serve>;
    stop: () => Promise<void>;
    url: string;
}

/**
 * Creates and starts the API server.
 * 
 * @param config - Server configuration options
 * @param config.port - Port to listen on (default: 3000)
 * @param config.hostname - Hostname to bind to (default: "localhost")
 * @returns Promise resolving to server instance with stop() method
 * 
 * @example
 * const server = await createWebServer({ port: 3000, hostname: "0.0.0.0" });
 * console.log(`Server running at ${server.url}`);
 * 
 * // To stop the server:
 * await server.stop();
 */
export async function createWebServer(config: WebServerConfig = {}): Promise<WebServerInstance> {
    const { port = 3000, hostname = "localhost" } = config;

    // Configuration constants
    const MAX_CONNECTIONS = 10;
    const MAX_PAYLOAD_BYTES = 16384; // 16KB
    const IDLE_TIMEOUT_SECONDS = 60;

    // Interval for broadcasting stats to all connected WS clients
    let statsBroadcastInterval: Timer | undefined;

    const server = serve({
        port,
        hostname,
        async fetch(req, server) {
            const url = new URL(req.url);

            // WebSocket upgrade handling
            if (url.pathname === "/ws") {
                const currentConnections = server.pendingWebSockets;
                if (currentConnections >= MAX_CONNECTIONS) {
                    logger.warn("web", `Connection rejected: limit reached (${currentConnections}/${MAX_CONNECTIONS})`);
                    return new Response("Connection limit reached", { status: 429 });
                }

                const success = server.upgrade(req);
                if (success) return undefined;
                return new Response("WebSocket upgrade failed", { status: 400 });
            }

            // Delegate to modular route handlers
            const response = await handleRequest(req, url);
            if (response) return response;

            // No matching route found
            return new Response("Not Found", { status: 404 });
        },

        websocket: {
            /**
             * Called when a WebSocket client connects.
             * Subscribes the client to the dashboard channel and sends initial stats.
             */
            open(ws) {
                ws.subscribe("dashboard");
                logger.debug("web", `Client connected. Total: ${server.pendingWebSockets}`);

                // Send initial stats
                getFullDashboardStats().then(stats => {
                    ws.send(JSON.stringify({ type: "STATS_UPDATE", data: stats }));
                });

                // Start broadcast interval if this is the first client
                if (!statsBroadcastInterval) {
                    statsBroadcastInterval = setInterval(async () => {
                        try {
                            const stats = await getFullDashboardStats();
                            server.publish("dashboard", JSON.stringify({ type: "STATS_UPDATE", data: stats }));
                        } catch (error) {
                            logger.error("web", "Error in stats broadcast", error);
                        }
                    }, 5000);
                }
            },

            /**
             * Called when a WebSocket message is received.
             * Handles PING/PONG heartbeat messages.
             */
            async message(ws, message) {
                try {
                    const messageStr = message.toString();

                    // Defense-in-depth: redundant length check before parsing
                    if (messageStr.length > MAX_PAYLOAD_BYTES) {
                        logger.error("web", "Payload exceeded maximum limit");
                        return;
                    }

                    const rawData = JSON.parse(messageStr);
                    const { WsMessageSchema } = await import("@shared/modules/dashboard/dashboard.types");
                    const parsed = WsMessageSchema.safeParse(rawData);

                    if (!parsed.success) {
                        logger.error("web", "Invalid message format", parsed.error.issues);
                        return;
                    }

                    if (parsed.data.type === "PING") {
                        ws.send(JSON.stringify({ type: "PONG" }));
                    }
                } catch (e) {
                    logger.error("web", "Failed to handle message", e);
                }
            },

            /**
             * Called when a WebSocket client disconnects.
             * Stops the broadcast interval if no clients remain.
             */
            close(ws) {
                ws.unsubscribe("dashboard");
                logger.debug("web", `Client disconnected. Total remaining: ${server.pendingWebSockets}`);

                // Stop broadcast interval if no clients left
                if (server.pendingWebSockets === 0 && statsBroadcastInterval) {
                    clearInterval(statsBroadcastInterval);
                    statsBroadcastInterval = undefined;
                }
            },
            maxPayloadLength: MAX_PAYLOAD_BYTES,
            idleTimeout: IDLE_TIMEOUT_SECONDS,
        },
    });

    // Listen for real-time events from the system bus
    const { systemEvents, EVENTS } = await import("@shared/lib/events");
    systemEvents.on(EVENTS.DASHBOARD.NEW_EVENT, (event) => {
        server.publish("dashboard", JSON.stringify({ type: "NEW_EVENT", data: event }));
    });

    const url = `http://${hostname}:${port}`;

    return {
        server,
        url,
        stop: async () => {
            if (statsBroadcastInterval) {
                clearInterval(statsBroadcastInterval);
            }
            server.stop(true);
        },
    };
}

/**
 * Starts the web server from the main application root.
 * Kept for backward compatibility.
 * 
 * @param webProjectPath - Deprecated, no longer used
 * @param config - Server configuration options
 * @returns Promise resolving to server instance
 */
export async function startWebServerFromRoot(
    webProjectPath: string,
    config: WebServerConfig = {}
): Promise<WebServerInstance> {
    return createWebServer(config);
}