import type { IncomingMessage, ServerResponse } from 'node:http';
import type { HostApiContext } from '../context';
import { PREVIEW_DATA_MAX_REQUEST_BYTES, PREVIEW_DATA_MAX_RESPONSE_BYTES, PREVIEW_DATA_ROUTE_ROOT, type PreviewDataSessionManager } from '../../services/preview-data-session';
import { sendNoContent } from '../route-utils';
import type {
  DataServiceErrorContext,
  DataServiceHostResult,
} from '../../../shared/data-service';
import {
  isRecord,
  parseCollection as parseCollectionSegment,
  parseCursor as parseCursorValue,
  parseData as parseDataValue,
  parseDocumentId as parseDocumentIdValue,
  parseIfMatch as parseIfMatchValue,
  parseLimit as parseLimitValue,
  readBoundedJson as readBoundedJsonBody,
  requireExactKeys as requireExactKeysValue,
  requireQueryKeys as requireQueryKeysValue,
  type ParserMessages,
} from './data-service-parsers';

const CORS_METHODS = 'GET, PUT, DELETE, OPTIONS';
const CORS_HEADERS = 'Authorization, Content-Type, If-Match';
const PARSER_MESSAGES: ParserMessages = {
  invalidRequest: 'Preview data request is invalid',
  invalidRevision: 'Data Service document revision is invalid',
  requestTooLarge: 'Preview data request is too large',
};

class PreviewDataRouteError extends Error {
  constructor(
    readonly status: number,
    readonly code: string,
    message: string,
    readonly retryable = false,
  ) {
    super(message);
    this.name = 'PreviewDataRouteError';
  }
}

function routeFailure<T>(
  status: number,
  code: string,
  message: string,
  retryable = false,
  extra: { retry_after_seconds?: number; context?: DataServiceErrorContext } = {},
): DataServiceHostResult<T> {
  return {
    success: false,
    status,
    code,
    error: message,
    retryable,
    ...(extra.retry_after_seconds === undefined ? {} : { retry_after_seconds: extra.retry_after_seconds }),
    ...(extra.context === undefined ? {} : { context: extra.context }),
    data: null,
  };
}

function unavailable<T>(): DataServiceHostResult<T> {
  return routeFailure(503, 'runtime_unavailable', 'Preview data runtime is unavailable', true);
}

function invalidResponse<T>(): DataServiceHostResult<T> {
  return routeFailure(502, 'upstream_invalid_response', 'Data Service returned an invalid response');
}

function isPreviewDataPath(pathname: string): boolean {
  return pathname === PREVIEW_DATA_ROUTE_ROOT || pathname.startsWith(`${PREVIEW_DATA_ROUTE_ROOT}/`);
}

function managerFor(ctx: HostApiContext): PreviewDataSessionManager | undefined {
  return ctx.previewDataSession ?? ctx.codingProducts?.previewDataSession;
}

function applyCors(res: ServerResponse, manager: PreviewDataSessionManager | undefined, req: IncomingMessage): void {
  const origin = manager?.corsOrigin(req);
  if (origin) {
    res.setHeader('Access-Control-Allow-Origin', origin);
    res.setHeader('Vary', 'Origin');
  }
  res.setHeader('Access-Control-Allow-Methods', CORS_METHODS);
  res.setHeader('Access-Control-Allow-Headers', CORS_HEADERS);
}

function serializeBounded(value: unknown): string | null {
  let encoded: string;
  try {
    encoded = JSON.stringify(value);
  } catch {
    return null;
  }
  if (typeof encoded !== 'string') return null;
  return Buffer.byteLength(encoded, 'utf8') <= PREVIEW_DATA_MAX_RESPONSE_BYTES
    ? encoded
    : null;
}

function sendBoundedJson(res: ServerResponse, status: number, payload: unknown): boolean {
  const encoded = serializeBounded(payload);
  if (encoded === null) return false;
  res.statusCode = status;
  res.setHeader('Content-Type', 'application/json; charset=utf-8');
  res.end(encoded);
  return true;
}

function sendError(res: ServerResponse, result: DataServiceHostResult<unknown>): void {
  const detail = {
    code: result.code ?? 'runtime_unavailable',
    message: result.error ?? 'Preview data runtime is unavailable',
    retryable: result.retryable,
    ...(result.context && Object.keys(result.context).length > 0 ? { context: result.context } : {}),
  };
  if (result.retry_after_seconds !== undefined) {
    res.setHeader('Retry-After', String(result.retry_after_seconds));
  }
  if (!sendBoundedJson(res, result.status >= 400 && result.status <= 599 ? result.status : 503, { detail })) {
    sendBoundedJson(res, 503, {
      detail: {
        code: 'runtime_unavailable',
        message: 'Preview data runtime is unavailable',
        retryable: true,
      },
    });
  }
}

function sendResult<T>(res: ServerResponse, result: DataServiceHostResult<T>): void {
  res.setHeader('Cache-Control', 'private, no-store');
  if (!result.success) {
    sendError(res, result as DataServiceHostResult<unknown>);
    return;
  }
  if (result.status === 204) {
    sendNoContent(res);
    return;
  }
  if (result.data === null) {
    sendError(res, invalidResponse());
    return;
  }
  if (isRecord(result.data) && Number.isSafeInteger(result.data.revision) && result.data.revision > 0) {
    res.setHeader('ETag', `"${result.data.revision}"`);
  }
  if (!sendBoundedJson(res, result.status, result.data)) {
    sendError(res, invalidResponse());
  }
}

function parserFailure(status: number, code: string, message: string): never {
  throw new PreviewDataRouteError(status, code, message);
}

async function readBoundedJson(req: IncomingMessage): Promise<Record<string, unknown>> {
  return readBoundedJsonBody(req, PREVIEW_DATA_MAX_REQUEST_BYTES, parserFailure, PARSER_MESSAGES);
}

function requireExactKeys(value: Record<string, unknown>, keys: readonly string[]): void {
  requireExactKeysValue(value, keys, parserFailure, PARSER_MESSAGES.invalidRequest);
}

function parseCollection(value: string): string {
  return parseCollectionSegment(value, parserFailure, PARSER_MESSAGES.invalidRequest);
}

function parseDocumentId(value: string): string {
  return parseDocumentIdValue(value, parserFailure, PARSER_MESSAGES.invalidRequest);
}

function requireQueryKeys(url: URL, allowed: readonly string[]): void {
  requireQueryKeysValue(url, allowed, parserFailure, PARSER_MESSAGES.invalidRequest);
}

function parseLimit(url: URL): number | undefined {
  return parseLimitValue(url, parserFailure, PARSER_MESSAGES.invalidRequest);
}

function parseCursor(url: URL): string | undefined {
  return parseCursorValue(url, parserFailure, PARSER_MESSAGES.invalidRequest);
}

function parseIfMatch(req: IncomingMessage): number | undefined {
  return parseIfMatchValue(req, parserFailure, PARSER_MESSAGES.invalidRevision);
}

function parseData(value: unknown): Record<string, unknown> {
  return parseDataValue(value, parserFailure, PARSER_MESSAGES.invalidRequest);
}

function requireJsonContentType(req: IncomingMessage): void {
  const value = req.headers['content-type'];
  if (typeof value !== 'string' || value.split(';', 1)[0].trim().toLowerCase() !== 'application/json') {
    throw new PreviewDataRouteError(415, 'invalid_content_type', 'Preview data requests require application/json');
  }
}

function sendOptions(res: ServerResponse): void {
  res.statusCode = 204;
  res.end();
}

function operationsFor(ctx: HostApiContext) {
  return ctx.codingProducts?.dataService;
}

export async function handlePreviewDataRoutes(
  req: IncomingMessage,
  res: ServerResponse,
  url: URL,
  ctx: HostApiContext,
): Promise<boolean> {
  if (!isPreviewDataPath(url.pathname)) return false;

  const manager = managerFor(ctx);
  applyCors(res, manager, req);
  res.setHeader('Cache-Control', 'private, no-store');
  if (!manager) {
    sendError(res, unavailable());
    return true;
  }

  const authorization = manager.authorizeRequest(req);
  if (!authorization.ok) {
    sendError(res, routeFailure(
      authorization.status,
      authorization.code,
      authorization.message,
      authorization.retryable,
      authorization.retryAfterSeconds === undefined
        ? {}
        : { retry_after_seconds: authorization.retryAfterSeconds },
    ));
    return true;
  }

  const operations = operationsFor(ctx);
  if (!operations && authorization.method !== 'OPTIONS') {
    sendError(res, unavailable());
    return true;
  }

  const runOperation = async <T>(operation: () => Promise<DataServiceHostResult<T>>): Promise<void> => {
    if (!manager.isCurrentSession(authorization.session)) {
      sendError(res, unavailable());
      return;
    }
    const result = await operation();
    if (!manager.isCurrentSession(authorization.session)) {
      sendError(res, unavailable());
      return;
    }
    sendResult(res, result);
  };

  try {
    const method = authorization.method;
    const collectionPath = url.pathname.match(
      new RegExp(`^${PREVIEW_DATA_ROUTE_ROOT}/collections/([^/]+)/documents$`),
    );
    if (collectionPath) {
      const collection = parseCollection(collectionPath[1]);
      requireQueryKeys(url, ['limit', 'cursor']);
      if (method === 'OPTIONS') {
        sendOptions(res);
      } else if (method === 'GET') {
        await runOperation(() => operations!.listDocuments({
          collection,
          limit: parseLimit(url),
          cursor: parseCursor(url),
        }, authorization.session.projectPath));
      } else {
        sendError(res, routeFailure(405, 'method_not_allowed', 'Preview data method is not allowed'));
      }
      return true;
    }

    const documentPath = url.pathname.match(
      new RegExp(`^${PREVIEW_DATA_ROUTE_ROOT}/collections/([^/]+)/documents/([^/]+)$`),
    );
    if (documentPath) {
      const collection = parseCollection(documentPath[1]);
      const documentId = parseDocumentId(documentPath[2]);
      requireQueryKeys(url, []);
      if (method === 'OPTIONS') {
        sendOptions(res);
      } else if (method === 'GET') {
        await runOperation(() => operations!.getDocument(
          { collection, document_id: documentId },
          authorization.session.projectPath,
        ));
      } else if (method === 'PUT') {
        requireJsonContentType(req);
        const body = await readBoundedJson(req);
        requireExactKeys(body, ['data']);
        const ifRevision = parseIfMatch(req);
        await runOperation(() => operations!.putDocument({
          collection,
          document_id: documentId,
          data: parseData(body.data),
          ...(ifRevision === undefined ? {} : { if_revision: ifRevision }),
        }, authorization.session.projectPath));
      } else if (method === 'DELETE') {
        const ifRevision = parseIfMatch(req);
        await runOperation(() => operations!.deleteDocument({
          collection,
          document_id: documentId,
          ...(ifRevision === undefined ? {} : { if_revision: ifRevision }),
          confirmed: true,
        }, authorization.session.projectPath));
      } else {
        sendError(res, routeFailure(405, 'method_not_allowed', 'Preview data method is not allowed'));
      }
      return true;
    }

    sendError(res, routeFailure(404, 'route_not_found', 'Preview data route was not found'));
    return true;
  } catch (error) {
    if (error instanceof PreviewDataRouteError) {
      sendError(res, routeFailure(error.status, error.code, error.message, error.retryable));
      return true;
    }
    sendError(res, unavailable());
    return true;
  }
}

export const isPreviewDataRoute = isPreviewDataPath;