import { Hono, type MiddlewareHandler } from 'hono';
import { serve } from '@hono/node-server';
import { cors } from 'hono/cors';
import { compress } from 'hono/compress';
import { bodyLimit } from 'hono/body-limit';

import type { Logger } from '../utils/logger.ts';
import type { Config } from './config.ts';
import type { TransportRouter, UpgradeTransportRouter, AppEnv } from './transport/transport-router.ts';

/**
 * Owns the Hono server and installs transport adapters around shared middleware.
 *
 * Application routes are deliberately absent from this layer.
 */
export class ServerHost {
    private readonly debug: Logger;
    private server: ReturnType<typeof serve> | undefined;
    private stopPromise: Promise<void> | undefined;
    private readonly app: Hono<AppEnv>;

    /**
     * @param config - Server listen address, CORS, and related settings.
     * @param debug - Root logger extended with a server-host namespace.
     * @param transports - Protocol adapters registered onto the Hono app.
     */
    constructor(
        private readonly config: Config,
        debug: Logger,
        private readonly transports: TransportRouter[],
    ) {
        this.debug = debug.extend('server-host');
        this.app = new Hono<AppEnv>();
    }

    /** Configure middleware, register adapters, and begin listening. */
    async start(): Promise<void> {
        const { port, host, cors: corsConfig, maxRequestBodyBytes } = this.config.server;
        this.debug(`Starting on http://${host}:${port}`);

        const corsMiddleware = cors({
            origin: corsConfig.origin ?? '*',
            allowMethods: corsConfig.methods ?? [ 'POST', 'OPTIONS' ],
            allowHeaders: corsConfig.allowedHeaders ?? [ 'Content-Type', 'Accept' ],
        });

        this.app.use('*', corsMiddleware);

        // Reject oversized request bodies before any decoder or route reads them.
        // Hono checks Content-Length when it can and counts streamed chunks when it
        // cannot, covering both fixed-length and chunked HTTP requests.
        this.app.use('*', ServerHost.limitBodySizeMiddleware(maxRequestBodyBytes, this.debug));

        const compression = compress();

        // Compression can buffer event streams, so never apply it to requested SSE.
        this.app.use('*', async (c, next) => {
            if (c.req.header('accept')?.includes('text/event-stream')) {
                await next();

                return;
            }

            return compression(c, next);
        });

        this.app.get('/health', (c) => c.json({ status: 'ok' }));

        // Each transport adapter registers its own wire endpoints.
        for (const transport of this.transports) {
            await transport.register(this.app);
        }

        // The Node Hono server accepts one WebSocketServer instance per listener.
        const upgradeTransports = this.transports.filter((transport): transport is UpgradeTransportRouter => 'websocketServer' in transport);
        if (upgradeTransports.length > 1) {
            throw new Error('ServerHost supports only one WebSocket upgrade server');
        }

        const [ upgradeTransport ] = upgradeTransports;

        this.server = serve({
            fetch: this.app.fetch,
            port,
            hostname: host,
            ...(upgradeTransport ? { websocket: { server: upgradeTransport.websocketServer } } : {}),
        });

        // Wait for the server to start listening or timeout after 10 seconds.
        await Promise.race([
            // Wait for the server to start listening.
            new Promise((resolve) => {
                this.server?.once('listening', resolve);
            }),
            // Timeout after 10 seconds.
            new Promise((_resolve, reject) => {
                setTimeout(reject, 10000);
            }),
        ]);

        this.debug(`Started on http://${host}:${port}`);
    }

    /** Stop accepting traffic and close all transport-owned connections. */
    async stop(): Promise<void> {
        // If we are already shutting down, return the existing promise
        if (this.stopPromise) {
            return this.stopPromise;
        }

        // If the server hasn't been started yet or already shut down, return early
        const server = this.server;
        if (!server) {
            return;
        }

        // Create a promise that resolves when the server is closed
        this.debug('stopping server');
        const closeServer = new Promise<void>((resolve, reject) => {
            server.close((error) => (error ? reject(error) : resolve()));
        });

        // Close the transports
        const closeTransports = this.transports.map((transport) => Promise.resolve(transport.stop?.()));

        // Create a promise that resolves when the server and transports are closed
        this.stopPromise = Promise.all([ closeServer, ...closeTransports ]).then(() => {
            this.stopPromise = undefined;
        });

        // Return the promise
        return this.stopPromise;
    }

    /**
     * Build the server-wide Hono request-body limit policy.
     *
     * Keeping this policy in ServerHost ensures it runs before every HTTP adapter
     * without making application routes or connection streams aware of HTTP.
     * Hono preserves an accepted streamed body for downstream middleware, allowing
     * the Extended JSON decoder to read it normally after validation.
     *
     * @param maxRequestBodyBytes - Maximum encoded HTTP request body size in bytes.
     * @param debug - Logger used to record rejected requests and configured limits.
     * @returns Hono middleware which returns the shared public 413 error contract.
     */
    static limitBodySizeMiddleware(maxRequestBodyBytes: number, debug: Logger): MiddlewareHandler<AppEnv> {
        return bodyLimit({
            // Hono interprets maxSize as encoded request bytes, not decoded JSON size.
            maxSize: maxRequestBodyBytes,
            onError: (context) => {
                // Do not parse the rejected payload: Hono stopped consuming it at the cap.
                debug('request body exceeded configured %d byte limit: %s %s', maxRequestBodyBytes, context.req.method, context.req.path);

                // Limiting occurs before dispatch, so a normal HTTP 413 remains available.
                return context.json(
                    {
                        statusCode: 413,
                        error: `Request body exceeds the ${maxRequestBodyBytes} byte limit`,
                    },
                    413,
                );
            },
        });
    }
}