import { IncomingMessage, ServerResponse } from 'node:http';

type JsonValue = Record<string, unknown> | Array<unknown>;

export function sendJson(response: ServerResponse, statusCode: number, payload: JsonValue): void {
  const body = JSON.stringify(payload);
  response.writeHead(statusCode, {
    'Access-Control-Allow-Origin': '*',
    'Access-Control-Allow-Headers': 'Content-Type',
    'Access-Control-Allow-Methods': 'GET,POST,OPTIONS',
    'Content-Type': 'application/json; charset=utf-8',
    'Content-Length': Buffer.byteLength(body),
  });
  response.end(body);
}

export function readBody(request: IncomingMessage): Promise<Record<string, unknown>> {
  return new Promise((resolve) => {
    let body = '';
    request.on('data', (chunk) => {
      body += chunk;
    });
    request.on('end', () => {
      if (!body) {
        resolve({});
        return;
      }
      try {
        resolve(JSON.parse(body));
      } catch {
        resolve({});
      }
    });
  });
}

/**
 * 从 multipart/form-data 请求中读取上传文件
 * 简易实现，支持单文件上传
 */
export function readMultipartFile(request: IncomingMessage): Promise<{ fileName: string; buffer: Buffer }> {
  return new Promise((resolve, reject) => {
    const contentType = request.headers['content-type'] || '';
    const chunks: Buffer[] = [];

    request.on('data', (chunk: Buffer) => {
      chunks.push(chunk);
    });

    request.on('end', () => {
      const rawBuffer = Buffer.concat(chunks);

      if (contentType.includes('multipart/form-data')) {
        try {
          const result = parseMultipart(rawBuffer, contentType);
          resolve(result);
        } catch (error) {
          reject(error);
        }
      } else {
        // Treat as raw file upload with filename from header
        const disposition = request.headers['content-disposition'] || '';
        const fileNameMatch = disposition.match(/filename="?([^";\n]+)"?/);
        const fileName = fileNameMatch ? fileNameMatch[1] : 'upload.bin';
        resolve({ fileName, buffer: rawBuffer });
      }
    });

    request.on('error', reject);
  });
}

function parseMultipart(buffer: Buffer, contentType: string): { fileName: string; buffer: Buffer } {
  // 提取 boundary（可能带引号）
  const boundaryMatch = contentType.match(/boundary="?([^";\s]+)"?/);
  if (!boundaryMatch) {
    throw new Error('Missing multipart boundary');
  }

  const boundary = `--${boundaryMatch[1]}`;
  const boundaryBytes = Buffer.from(boundary, 'ascii');

  // 在 buffer 中按 boundary 定位各 part
  let pos = bufferIndexOf(buffer, boundaryBytes, 0);
  if (pos === -1) {
    throw new Error('No file found in multipart data');
  }

  // 跳过第一个 boundary + CRLF
  pos += boundaryBytes.length + 2;

  while (pos < buffer.length) {
    // 找到 header/body 分隔的 \r\n\r\n
    const headerEndMarker = Buffer.from('\r\n\r\n', 'ascii');
    const headerEnd = bufferIndexOf(buffer, headerEndMarker, pos);
    if (headerEnd === -1) break;

    const headersStr = buffer.subarray(pos, headerEnd).toString('utf-8');
    const bodyStart = headerEnd + 4;

    // 找下一个 boundary
    const nextBoundary = bufferIndexOf(buffer, boundaryBytes, bodyStart);
    // body 结束于下一个 boundary 前的 \r\n
    const bodyEnd = nextBoundary === -1 ? buffer.length : nextBoundary - 2;

    // 检查是否有 filename
    const fileNameMatch = headersStr.match(/filename="?([^";\r\n]+)"?/);
    if (fileNameMatch) {
      const fileName = decodeFileName(fileNameMatch[1].trim());
      const fileBuffer = buffer.subarray(bodyStart, bodyEnd);
      return { fileName, buffer: fileBuffer };
    }

    // 跳到下一个 part
    if (nextBoundary === -1) break;
    pos = nextBoundary + boundaryBytes.length;
    // 跳过 CRLF 或 -- (结束标记)
    if (buffer[pos] === 0x2d && buffer[pos + 1] === 0x2d) break; // '--' = end
    pos += 2; // skip \r\n
  }

  throw new Error('No file found in multipart data');
}

function bufferIndexOf(buf: Buffer, search: Buffer, fromIndex: number): number {
  for (let i = fromIndex; i <= buf.length - search.length; i++) {
    let found = true;
    for (let j = 0; j < search.length; j++) {
      if (buf[i + j] !== search[j]) {
        found = false;
        break;
      }
    }
    if (found) return i;
  }
  return -1;
}

function decodeFileName(name: string): string {
  try {
    return decodeURIComponent(name);
  } catch {
    return name;
  }
}

/**
 * 从 URL 中提取路径参数
 * 例如: extractPathParam('/api/tasks/abc123', '/api/tasks/') => 'abc123'
 */
export function extractPathParam(pathname: string, prefix: string): string {
  if (!pathname.startsWith(prefix)) return '';
  const rest = pathname.substring(prefix.length);
  const slashIndex = rest.indexOf('/');
  return slashIndex === -1 ? rest : rest.substring(0, slashIndex);
}

/**
 * 提取路径尾部
 * 例如: extractPathTail('/api/tasks/abc123/export', '/api/tasks/') => 'abc123/export'
 */
export function extractPathTail(pathname: string, prefix: string): string {
  if (!pathname.startsWith(prefix)) return '';
  return pathname.substring(prefix.length);
}