export interface Env {
  R2: R2Bucket;
  PROJECT_NAME: string;
  WORKER_URL: string;
}

authenticate request
→ authorize the project/user action
→ validate size and media policy
→ generate or normalize a scoped object key
→ call env.R2
→ return a sanitized response

const FILE_ID_RE = /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i;

function ownerPrefix(userId: string): string {
  if (!userId) throw new Error('Authenticated user id is required');
  return `users/${encodeURIComponent(userId)}/files/`;
}

function objectKey(userId: string, fileId: string): string {
  if (!FILE_ID_RE.test(fileId)) throw new Error('Invalid file id');
  return `${ownerPrefix(userId)}${fileId}`;
}

const MAX_UPLOAD_BYTES = 25 * 1024 * 1024;
const ALLOWED_CONTENT_TYPES = new Set([
  'image/jpeg',
  'image/png',
  'image/webp',
  'application/pdf',
]);

function json(data: unknown, status = 200): Response {
  return Response.json(data, { status });
}

function safeDownloadName(value: string | null): string {
  const cleaned = (value || 'download')
    .replace(/[\r\n"\\]/g, '_')
    .replace(/[\x00-\x1f\x7f]/g, '')
    .trim();
  return (cleaned || 'download').slice(0, 128);
}

function requestedFileId(request: Request): string | null {
  const url = new URL(request.url);
  const value = url.pathname.split('/').filter(Boolean).at(-1) || '';
  return FILE_ID_RE.test(value) ? value : null;
}

async function handleUpload(
  request: Request,
  env: Env,
  userId: string,
): Promise<Response> {
  if (!request.body) return json({ error: 'File body is required' }, 400);

  const lengthHeader = request.headers.get('content-length');
  if (!lengthHeader) return json({ error: 'Content-Length is required' }, 411);

  const declaredSize = Number(lengthHeader);
  if (!Number.isSafeInteger(declaredSize) || declaredSize < 0) {
    return json({ error: 'Invalid Content-Length' }, 400);
  }
  if (declaredSize > MAX_UPLOAD_BYTES) {
    return json({ error: 'File is too large' }, 413);
  }

  const contentType = (request.headers.get('content-type') || '')
    .split(';', 1)[0]
    .trim()
    .toLowerCase();
  if (!ALLOWED_CONTENT_TYPES.has(contentType)) {
    return json({ error: 'Unsupported media type' }, 400);
  }

  const fileId = crypto.randomUUID();
  const key = objectKey(userId, fileId);
  const filename = safeDownloadName(request.headers.get('x-file-name'));

  const object = await env.R2.put(key, request.body, {
    httpMetadata: {
      contentType,
      contentDisposition: `attachment; filename="${filename}"`,
    },
    customMetadata: { ownerId: userId },
  });

  if (object === null) return json({ error: 'Upload precondition failed' }, 412);

  // Content-Length is only a precheck. Enforce the actual stored size too.
  if (object.size > MAX_UPLOAD_BYTES) {
    await env.R2.delete(key);
    return json({ error: 'File is too large' }, 413);
  }

  return json({ id: fileId, size: object.size, etag: object.httpEtag }, 201);
}

function validRangeHeader(value: string | null): boolean {
  if (!value) return true;
  const match = /^bytes=(\d*)-(\d*)$/.exec(value);
  return Boolean(match && (match[1] || match[2]));
}

async function handleDownload(
  request: Request,
  env: Env,
  userId: string,
): Promise<Response> {
  const fileId = requestedFileId(request);
  if (!fileId) return json({ error: 'Invalid file id' }, 400);
  if (!validRangeHeader(request.headers.get('range'))) {
    return json({ error: 'Invalid Range header' }, 416);
  }

  const object = await env.R2.get(objectKey(userId, fileId), {
    onlyIf: request.headers,
    range: request.headers,
  });
  if (object === null) return json({ error: 'Not found' }, 404);
  if (!('body' in object)) return new Response(null, { status: 412 });

  const headers = new Headers();
  object.writeHttpMetadata(headers);
  headers.set('etag', object.httpEtag);
  headers.set('accept-ranges', 'bytes');
  if (object.range) {
    const { offset, length } = object.range;
    headers.set(
      'content-range',
      `bytes ${offset}-${offset + length - 1}/${object.size}`,
    );
    headers.set('content-length', String(length));
  } else {
    headers.set('content-length', String(object.size));
  }

  return new Response(object.body, {
    status: object.range ? 206 : 200,
    headers,
  });
}

async function handleHead(
  request: Request,
  env: Env,
  userId: string,
): Promise<Response> {
  const fileId = requestedFileId(request);
  if (!fileId) return json({ error: 'Invalid file id' }, 400);

  const object = await env.R2.head(objectKey(userId, fileId));
  if (object === null) return new Response(null, { status: 404 });

  const headers = new Headers();
  object.writeHttpMetadata(headers);
  headers.set('etag', object.httpEtag);
  headers.set('content-length', String(object.size));
  return new Response(null, { status: 200, headers });
}

async function handleDelete(
  request: Request,
  env: Env,
  userId: string,
): Promise<Response> {
  const fileId = requestedFileId(request);
  if (!fileId) return json({ error: 'Invalid file id' }, 400);

  const key = objectKey(userId, fileId);
  const object = await env.R2.head(key);
  if (object === null) return json({ error: 'Not found' }, 404);

  await env.R2.delete(key);
  return new Response(null, { status: 204 });
}

async function handleList(
  request: Request,
  env: Env,
  userId: string,
): Promise<Response> {
  const cursor = new URL(request.url).searchParams.get('cursor');
  if (cursor && cursor.length > 2048) {
    return json({ error: 'Invalid cursor' }, 400);
  }

  const page = await env.R2.list({
    prefix: ownerPrefix(userId),
    cursor: cursor || undefined,
    limit: 100,
    include: ['httpMetadata', 'customMetadata'],
  });

  return json({
    objects: page.objects.map((object) => ({
      id: object.key.slice(ownerPrefix(userId).length),
      size: object.size,
      uploaded: object.uploaded.toISOString(),
      etag: object.httpEtag,
      contentType: object.httpMetadata?.contentType,
    })),
    nextCursor: page.truncated ? page.cursor : null,
  });
}

insert D1 row with status=pending
→ stream body to R2
→ update D1 row to status=ready