import type { IncomingMessage } from 'node:http';

export const MAX_CURSOR_LENGTH = 1_024;
export const COLLECTION_PATTERN = /^[a-z][a-z0-9_-]{0,47}$/;
export const DOCUMENT_ID_PATTERN = /^[A-Za-z0-9._~-]{1,128}$/;

export type ParserFailure = (
  status: number,
  code: string,
  message: string,
) => never;

export type ParserMessages = Readonly<{
  invalidRequest: string;
  invalidRevision: string;
  requestTooLarge: string;
}>;

export function isRecord(value: unknown): value is Record<string, unknown> {
  return typeof value === 'object' && value !== null && !Array.isArray(value);
}

export function boundedString(value: unknown, maximum: number): string | null {
  if (typeof value !== 'string') return null;
  return value && value.length <= maximum ? value : null;
}

export async function readBoundedJson(
  req: IncomingMessage,
  maxBytes: number,
  fail: ParserFailure,
  messages: ParserMessages,
): Promise<Record<string, unknown>> {
  const declared = req.headers['content-length'];
  const declaredValue = Array.isArray(declared) ? declared[0] : declared;
  if (declaredValue && /^\d+$/.test(declaredValue) && Number(declaredValue) > maxBytes) {
    return fail(413, 'request_too_large', messages.requestTooLarge);
  }
  const chunks: Buffer[] = [];
  let size = 0;
  for await (const chunk of req) {
    const buffer = Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk);
    size += buffer.byteLength;
    if (size > maxBytes) {
      return fail(413, 'request_too_large', messages.requestTooLarge);
    }
    chunks.push(buffer);
  }
  try {
    const value = JSON.parse(Buffer.concat(chunks).toString('utf8')) as unknown;
    if (!isRecord(value)) throw new Error('object required');
    return value;
  } catch {
    return fail(422, 'invalid_request', messages.invalidRequest);
  }
}

export function requireExactKeys(
  value: Record<string, unknown>,
  keys: readonly string[],
  fail: ParserFailure,
  message: string,
): void {
  const expected = new Set(keys);
  if (Object.keys(value).some((key) => !expected.has(key))
    || keys.some((key) => !Object.prototype.hasOwnProperty.call(value, key))) {
    fail(422, 'invalid_request', message);
  }
}

function decodeSegment(
  value: string,
  maximum: number,
  pattern: RegExp,
  fail: ParserFailure,
  message: string,
): string {
  let decoded: string;
  try {
    decoded = decodeURIComponent(value);
  } catch {
    return fail(422, 'invalid_request', message);
  }
  if (decoded.length > maximum || !pattern.test(decoded)) {
    return fail(422, 'invalid_request', message);
  }
  return decoded;
}

export function parseCollection(
  value: string,
  fail: ParserFailure,
  message: string,
): string {
  return decodeSegment(value, 48, COLLECTION_PATTERN, fail, message);
}

export function parseDocumentId(
  value: string,
  fail: ParserFailure,
  message: string,
): string {
  const documentId = decodeSegment(value, 128, DOCUMENT_ID_PATTERN, fail, message);
  if (documentId === '.' || documentId === '..') {
    return fail(422, 'invalid_request', message);
  }
  return documentId;
}

export function requireQueryKeys(
  url: URL,
  allowed: readonly string[],
  fail: ParserFailure,
  message: string,
): void {
  const accepted = new Set(allowed);
  if ([...url.searchParams.keys()].some((key) => !accepted.has(key))) {
    fail(422, 'invalid_request', message);
  }
}

export function parseLimit(
  url: URL,
  fail: ParserFailure,
  message: string,
): number | undefined {
  const values = url.searchParams.getAll('limit');
  if (values.length === 0) return undefined;
  if (values.length !== 1 || !/^[1-9]\d*$/.test(values[0])) {
    return fail(422, 'invalid_request', message);
  }
  const limit = Number(values[0]);
  if (!Number.isSafeInteger(limit) || limit < 1 || limit > 100) {
    return fail(422, 'invalid_request', message);
  }
  return limit;
}

export function parseCursor(
  url: URL,
  fail: ParserFailure,
  message: string,
): string | undefined {
  const values = url.searchParams.getAll('cursor');
  if (values.length === 0) return undefined;
  const cursor = values.length === 1 ? boundedString(values[0], MAX_CURSOR_LENGTH) : null;
  if (!cursor) return fail(422, 'invalid_request', message);
  return cursor;
}

export function parseIfMatch(
  req: IncomingMessage,
  fail: ParserFailure,
  message: string,
): number | undefined {
  const value = req.headers['if-match'];
  if (value === undefined) return undefined;
  if (Array.isArray(value) || !/^"[1-9]\d*"$/.test(value)) {
    return fail(422, 'invalid_revision', message);
  }
  const revision = Number(value.slice(1, -1));
  if (!Number.isSafeInteger(revision) || revision < 1) {
    return fail(422, 'invalid_revision', message);
  }
  return revision;
}

export function parseData(
  value: unknown,
  fail: ParserFailure,
  message: string,
): Record<string, unknown> {
  if (!isRecord(value)) {
    return fail(422, 'invalid_request', message);
  }
  return value;
}