import { Readable, Writable } from 'node:stream';
import type { IncomingHttpHeaders, IncomingMessage, ServerResponse } from 'node:http';
import type { HostApiContext } from './context';
import { hostApiRouteHandlers } from './route-handlers';
import { requireJsonContentType, sendJson } from './route-utils';

export type HostApiDispatchInput = {
  path: string;
  method?: string;
  headers?: Record<string, string>;
  body?: string;
};

export type HostApiDispatchData = {
  status: number;
  ok: boolean;
  json?: unknown;
  text?: string;
};

class DispatchResponse extends Writable {
  statusCode = 200;
  statusMessage?: string;
  headersSent = false;
  socket = null;

  private readonly headers = new Map<string, string | string[]>();
  private readonly chunks: Buffer[] = [];

  constructor() {
    super({
      write: (chunk: Buffer | string, _encoding, callback) => {
        this.chunks.push(Buffer.isBuffer(chunk) ? Buffer.from(chunk) : Buffer.from(chunk));
        callback();
      },
    });
  }

  setHeader(name: string, value: string | number | readonly string[]): this {
    this.headers.set(name.toLowerCase(), Array.isArray(value) ? [...value] : String(value));
    return this;
  }

  getHeader(name: string): string | string[] | undefined {
    return this.headers.get(name.toLowerCase());
  }

  hasHeader(name: string): boolean {
    return this.headers.has(name.toLowerCase());
  }

  removeHeader(name: string): void {
    this.headers.delete(name.toLowerCase());
  }

  writeHead(
    statusCode: number,
    statusMessageOrHeaders?: string | Record<string, string | number | readonly string[]>,
    maybeHeaders?: Record<string, string | number | readonly string[]>,
  ): this {
    this.statusCode = statusCode;
    if (typeof statusMessageOrHeaders === 'string') {
      this.statusMessage = statusMessageOrHeaders;
      for (const [name, value] of Object.entries(maybeHeaders ?? {})) this.setHeader(name, value);
    } else {
      for (const [name, value] of Object.entries(statusMessageOrHeaders ?? {})) this.setHeader(name, value);
    }
    this.headersSent = true;
    return this;
  }

  flushHeaders(): void {
    this.headersSent = true;
  }

  body(): Buffer {
    return Buffer.concat(this.chunks);
  }

  contentType(): string {
    const value = this.getHeader('content-type');
    return Array.isArray(value) ? value[0] ?? '' : value ?? '';
  }
}

function createRequest(input: HostApiDispatchInput): IncomingMessage {
  const body = input.body ?? '';
  const request = Readable.from(body ? [Buffer.from(body, 'utf8')] : []) as Readable & Partial<IncomingMessage>;
  const headers: IncomingHttpHeaders = Object.create(null) as IncomingHttpHeaders;
  for (const [name, value] of Object.entries(input.headers ?? {})) {
    headers[name.toLowerCase()] = value;
  }
  if (body && headers['content-length'] === undefined) {
    headers['content-length'] = String(Buffer.byteLength(body, 'utf8'));
  }
  request.method = (input.method ?? 'GET').toUpperCase();
  request.url = input.path;
  request.headers = headers;
  return request as IncomingMessage;
}

function readResponseData(response: DispatchResponse): HostApiDispatchData {
  const body = response.body();
  if (response.statusCode === 204 || body.length === 0) {
    return { status: response.statusCode, ok: response.statusCode >= 200 && response.statusCode < 300 };
  }
  const text = body.toString('utf8');
  if (response.contentType().toLowerCase().includes('json')) {
    try {
      return {
        status: response.statusCode,
        ok: response.statusCode >= 200 && response.statusCode < 300,
        json: JSON.parse(text) as unknown,
      };
    } catch {
      // Keep malformed route output observable to the Renderer instead of
      // silently treating it as an empty response.
    }
  }
  return {
    status: response.statusCode,
    ok: response.statusCode >= 200 && response.statusCode < 300,
    text,
  };
}

/**
 * Dispatch a Renderer Host API request without a second IPC -> loopback HTTP
 * hop. This adapter deliberately reuses the existing Node route handlers so
 * authentication, validation and response contracts remain unchanged.
 */
export async function dispatchHostApiRequest(
  ctx: HostApiContext,
  input: HostApiDispatchInput,
): Promise<HostApiDispatchData> {
  const request = createRequest(input);
  const response = new DispatchResponse();
  const url = new URL(input.path, 'http://127.0.0.1');

  try {
    if (!requireJsonContentType(request)) {
      sendJson(response as unknown as ServerResponse, 415, {
        success: false,
        error: 'Content-Type must be application/json',
      });
      return readResponseData(response);
    }

    for (const handler of hostApiRouteHandlers) {
      if (await handler(request, response as unknown as ServerResponse, url, ctx)) {
        return readResponseData(response);
      }
    }
    sendJson(response as unknown as ServerResponse, 404, {
      success: false,
      error: `No route for ${request.method} ${url.pathname}`,
    });
    return readResponseData(response);
  } catch (error) {
    if (!response.headersSent && !response.writableEnded) {
      sendJson(response as unknown as ServerResponse, 500, {
        success: false,
        error: error instanceof Error ? error.message : String(error),
      });
      return readResponseData(response);
    }
    throw error;
  }
}