import fs from 'node:fs';
import path from 'node:path';
import { fileURLToPath } from 'node:url';

type ReferenceConfig = {
  references: Array<{
    source: string;
    target: string;
  }>;
};

type ZipEntry = {
  name: string;
  content: Buffer;
};

const scriptDir = path.dirname(fileURLToPath(import.meta.url));
const agentDir = path.resolve(scriptDir, '..');
const rootDir = path.resolve(agentDir, '../..');
const sourceDir = path.join(agentDir, 'source');
const tempDir = path.join(agentDir, '.tmp');
const packageName = 'frontend-architect';
const packageDir = path.join(tempDir, packageName);
const publicAgentsDir = path.join(rootDir, 'public', 'agents');
const zipPath = path.join(publicAgentsDir, `${packageName}.zip`);

function readJson<T>(filePath: string): T {
  return JSON.parse(fs.readFileSync(filePath, 'utf8')) as T;
}

function copyFile(sourcePath: string, targetPath: string) {
  fs.mkdirSync(path.dirname(targetPath), { recursive: true });
  fs.copyFileSync(sourcePath, targetPath);
}

function collectFiles(dir: string, baseDir = dir): ZipEntry[] {
  return fs
    .readdirSync(dir, { withFileTypes: true })
    .flatMap((entry) => {
      const entryPath = path.join(dir, entry.name);

      if (entry.isDirectory()) {
        return collectFiles(entryPath, baseDir);
      }

      const relativePath = path.relative(baseDir, entryPath).split(path.sep).join('/');

      return [
        {
          name: `${packageName}/${relativePath}`,
          content: fs.readFileSync(entryPath),
        },
      ];
    })
    .sort((a, b) => a.name.localeCompare(b.name));
}

function createCrc32Table() {
  return Array.from({ length: 256 }, (_, index) => {
    let value = index;

    for (let bit = 0; bit < 8; bit += 1) {
      value = value & 1 ? 0xedb88320 ^ (value >>> 1) : value >>> 1;
    }

    return value >>> 0;
  });
}

const crc32Table = createCrc32Table();

function crc32(buffer: Buffer) {
  let crc = 0xffffffff;

  for (const byte of buffer) {
    crc = crc32Table[(crc ^ byte) & 0xff] ^ (crc >>> 8);
  }

  return (crc ^ 0xffffffff) >>> 0;
}

function writeUInt16(value: number) {
  const buffer = Buffer.alloc(2);
  buffer.writeUInt16LE(value, 0);
  return buffer;
}

function writeUInt32(value: number) {
  const buffer = Buffer.alloc(4);
  buffer.writeUInt32LE(value >>> 0, 0);
  return buffer;
}

function createZip(entries: ZipEntry[]) {
  const localParts: Buffer[] = [];
  const centralParts: Buffer[] = [];
  const dosTime = 0;
  const dosDate = ((2026 - 1980) << 9) | (1 << 5) | 1;
  let offset = 0;

  for (const entry of entries) {
    const fileName = Buffer.from(entry.name, 'utf8');
    const checksum = crc32(entry.content);
    const size = entry.content.length;

    const localHeader = Buffer.concat([
      writeUInt32(0x04034b50),
      writeUInt16(20),
      writeUInt16(0),
      writeUInt16(0),
      writeUInt16(dosTime),
      writeUInt16(dosDate),
      writeUInt32(checksum),
      writeUInt32(size),
      writeUInt32(size),
      writeUInt16(fileName.length),
      writeUInt16(0),
      fileName,
    ]);

    localParts.push(localHeader, entry.content);

    const centralHeader = Buffer.concat([
      writeUInt32(0x02014b50),
      writeUInt16(20),
      writeUInt16(20),
      writeUInt16(0),
      writeUInt16(0),
      writeUInt16(dosTime),
      writeUInt16(dosDate),
      writeUInt32(checksum),
      writeUInt32(size),
      writeUInt32(size),
      writeUInt16(fileName.length),
      writeUInt16(0),
      writeUInt16(0),
      writeUInt16(0),
      writeUInt16(0),
      writeUInt32(0),
      writeUInt32(offset),
      fileName,
    ]);

    centralParts.push(centralHeader);
    offset += localHeader.length + size;
  }

  const centralDirectory = Buffer.concat(centralParts);
  const endOfCentralDirectory = Buffer.concat([
    writeUInt32(0x06054b50),
    writeUInt16(0),
    writeUInt16(0),
    writeUInt16(entries.length),
    writeUInt16(entries.length),
    writeUInt32(centralDirectory.length),
    writeUInt32(offset),
    writeUInt16(0),
  ]);

  return Buffer.concat([...localParts, centralDirectory, endOfCentralDirectory]);
}

function buildAgent() {
  const referencesConfig = readJson<ReferenceConfig>(path.join(sourceDir, 'references.json'));

  fs.rmSync(tempDir, { recursive: true, force: true });
  fs.mkdirSync(packageDir, { recursive: true });

  copyFile(path.join(sourceDir, 'AGENT.md'), path.join(packageDir, 'AGENT.md'));
  copyFile(path.join(sourceDir, 'manifest.json'), path.join(packageDir, 'manifest.json'));

  for (const reference of referencesConfig.references) {
    const sourcePath = path.join(rootDir, reference.source);

    if (!fs.existsSync(sourcePath)) {
      throw new Error(`Reference not found: ${reference.source}`);
    }

    copyFile(sourcePath, path.join(packageDir, reference.target));
  }

  fs.mkdirSync(publicAgentsDir, { recursive: true });
  fs.writeFileSync(zipPath, createZip(collectFiles(packageDir)));
  fs.rmSync(tempDir, { recursive: true, force: true });

  console.log(`Built ${path.relative(rootDir, zipPath)}`);
}

buildAgent();