import type { IncomingMessage, ServerResponse } from 'node:http';
import busboy, { type Busboy } from 'busboy';
import createError, { type HttpError } from 'http-errors';
import objectPath from 'object-path';
import { type ReadStreamOptions, WriteStream } from './fs-capacitor';
import { ignoreStream } from './ignore-stream';
import { type FileUpload, Upload } from './upload';
import { DEFAULT_MAX_FIELD_SIZE, DEFAULT_MAX_FILE_SIZE, DEFAULT_MAX_FILES } from './validation';

export const GRAPHQL_MULTIPART_REQUEST_SPEC_URL =
  'https://github.com/jaydenseric/graphql-multipart-request-spec' as const;

export interface UploadOptions {
  /**
   * Maximum allowed size for non-file form fields (in bytes).
   * This limits the size of text fields like 'operations' and 'map' JSON.
   * @default 1_000_000 (1MB)
   */
  maxFieldSize?: number;

  /**
   * Maximum allowed size for uploaded files (in bytes).
   * This limits the size of actual file content being uploaded.
   * @default 5_000_000 (5MB)
   */
  maxFileSize?: number;

  /**
   * Maximum number of files allowed in a single request.
   * @default Infinity
   */
  maxFiles?: number;
}

export interface GraphQLOperation {
  query: string;
  operationName?: string | null;
  variables?: Record<string, unknown> | null;
}

export type IncomingReq = Pick<
  IncomingMessage,
  'headers' | 'pipe' | 'unpipe' | 'once' | 'resume' | 'readableEnded'
> & {
  body?: string;
  rawBody?: string;
  req?: IncomingMessage;
};

export async function processRequest<T = GraphQLOperation | GraphQLOperation[]>(
  request: IncomingReq,
  response: Pick<ServerResponse, 'once'>,
  options?: UploadOptions
): Promise<T> {
  const {
    maxFieldSize = DEFAULT_MAX_FIELD_SIZE,
    maxFileSize = DEFAULT_MAX_FILE_SIZE,
    maxFiles = DEFAULT_MAX_FILES,
  } = options ?? {};

  return new Promise((resolve, reject) => {
    let released = false;

    let exitError: Error | undefined;

    let operations: T | undefined;

    let operationsPath: ReturnType<typeof objectPath> | undefined;

    let map: Map<string, Upload> | undefined;

    const parser: Busboy = busboy({
      headers: request.headers,
      defParamCharset: 'utf8',
      limits: {
        fieldSize: maxFieldSize,
        fields: 2, // Only operations and map.
        fileSize: maxFileSize,
        files: maxFiles,
      },
    });

    function exit(error: Error | HttpError, isParserError = false): void {
      if (exitError) return;

      exitError = error;

      if (map) {
        for (const upload of map.values()) {
          if (!upload.file) upload.reject(exitError);
        }
      }

      // If the error came from the parser, don’t cause it to be emitted again.
      if (isParserError) {
        parser.destroy();
      } else {
        parser.destroy(exitError);
      }

      request.unpipe(parser as unknown as NodeJS.ReadWriteStream);

      // With a sufficiently large request body, subsequent events in the same
      // event frame cause the stream to pause after the parser is destroyed. To
      // ensure that the request resumes, the call to .resume() is scheduled for
      // later in the event loop.
      setImmediate(() => request.resume());

      reject(exitError);
    }

    parser.on('field', (fieldName, value, { valueTruncated }) => {
      if (valueTruncated)
        return exit(
          createError(
            413,
            `The ‘${fieldName}’ multipart field value exceeds the ${maxFieldSize} byte size limit.`
          )
        );

      switch (fieldName) {
        case 'operations':
          try {
            operations = JSON.parse(value);
          } catch (_error) {
            return exit(
              createError(
                400,
                `Invalid JSON in the ‘operations’ multipart field (${GRAPHQL_MULTIPART_REQUEST_SPEC_URL}).`
              )
            );
          }

          // `operations` should be an object or an array. Note that arrays
          // and `null` have an `object` type.
          if (typeof operations !== 'object' || !operations)
            return exit(
              createError(
                400,
                `Invalid type for the ‘operations’ multipart field (${GRAPHQL_MULTIPART_REQUEST_SPEC_URL}).`
              )
            );

          operationsPath = objectPath(operations);

          break;
        case 'map': {
          if (!operations)
            return exit(
              createError(
                400,
                `Disordered multipart fields; ‘map’ should follow ‘operations’ (${GRAPHQL_MULTIPART_REQUEST_SPEC_URL}).`
              )
            );

          let parsedMap: Record<string, unknown>;
          try {
            parsedMap = JSON.parse(value);
          } catch (_error) {
            return exit(
              createError(
                400,
                `Invalid JSON in the ‘map’ multipart field (${GRAPHQL_MULTIPART_REQUEST_SPEC_URL}).`
              )
            );
          }

          // `map` should be an object.
          if (typeof parsedMap !== 'object' || !parsedMap || Array.isArray(parsedMap))
            return exit(
              createError(
                400,
                `Invalid type for the ‘map’ multipart field (${GRAPHQL_MULTIPART_REQUEST_SPEC_URL}).`
              )
            );

          const mapEntries = Object.entries(parsedMap);

          // Check max files is not exceeded, even though the number of files
          // to parse might not match the map provided by the client.
          if (mapEntries.length > maxFiles)
            return exit(createError(413, `${maxFiles} max file uploads exceeded.`));

          map = new Map();
          for (const [fieldName, paths] of mapEntries) {
            if (!Array.isArray(paths))
              return exit(
                createError(
                  400,
                  `Invalid type for the ‘map’ multipart field entry key ‘${fieldName}’ array (${GRAPHQL_MULTIPART_REQUEST_SPEC_URL}).`
                )
              );

            map.set(fieldName, new Upload());

            for (const [index, path] of paths.entries()) {
              if (typeof path !== 'string')
                return exit(
                  createError(
                    400,
                    `Invalid type for the ‘map’ multipart field entry key ‘${fieldName}’ array index ‘${index}’ value (${GRAPHQL_MULTIPART_REQUEST_SPEC_URL}).`
                  )
                );

              try {
                if (operationsPath?.get(path) !== null) {
                  throw new Error('Invalid object path');
                }

                operationsPath?.set(path, map.get(fieldName));
              } catch (_error) {
                return exit(
                  createError(
                    400,
                    `Invalid object path for the ‘map’ multipart field entry key ‘${fieldName}’ array index ‘${index}’ value ‘${path}’ (${GRAPHQL_MULTIPART_REQUEST_SPEC_URL}).`
                  )
                );
              }
            }
          }

          resolve(operations as T);
        }
      }
    });

    parser.on('file', (fieldName, stream, { filename, encoding, mimeType: mimetype }) => {
      if (!map) {
        ignoreStream(stream);
        return exit(
          createError(
            400,
            `Disordered multipart fields; files should follow ‘map’ (${GRAPHQL_MULTIPART_REQUEST_SPEC_URL}).`
          )
        );
      }

      const upload = map.get(fieldName);

      if (!upload) {
        // The file is extraneous. As the rest can still be processed, just
        // ignore it and don’t exit with an error.
        ignoreStream(stream);
        return;
      }

      let fileError: Error | undefined;

      const capacitor = new WriteStream();

      capacitor.on('error', () => {
        stream.unpipe();
        stream.resume();
      });

      stream.on('limit', () => {
        fileError = createError(
          413,
          `File truncated as it exceeds the ${maxFileSize} byte size limit.`
        );
        stream.unpipe();
        capacitor.destroy(fileError);
      });

      stream.on('error', (error) => {
        fileError = error;
        stream.unpipe();
        capacitor.destroy(fileError);
      });

      const file: FileUpload = {
        fieldName,
        filename,
        mimetype,
        encoding,
        createReadStream(options?: ReadStreamOptions) {
          const error = fileError || (released ? exitError : null);
          if (error) throw error;
          return capacitor.createReadStream(options);
        },
        capacitor,
      };

      Object.defineProperty(file, 'capacitor', {
        enumerable: false,
        configurable: false,
        writable: false,
      });

      stream.pipe(capacitor);
      upload.resolve(file);
    });

    parser.once('filesLimit', () =>
      exit(createError(413, `${maxFiles} max file uploads exceeded.`))
    );

    parser.once('finish', () => {
      request.unpipe(parser as unknown as NodeJS.ReadWriteStream);
      request.resume();

      if (!operations)
        return exit(
          createError(
            400,
            `Missing multipart field ‘operations’ (${GRAPHQL_MULTIPART_REQUEST_SPEC_URL}).`
          )
        );

      if (!map)
        return exit(
          createError(400, `Missing multipart field ‘map’ (${GRAPHQL_MULTIPART_REQUEST_SPEC_URL}).`)
        );

      for (const upload of map.values())
        if (!upload.file) upload.reject(createError(400, 'File missing in the request.'));
    });

    // Use the `on` method instead of `once` as in edge cases the same parser
    // could have multiple `error` events and all must be handled to prevent the
    // Node.js process exiting with an error. One edge case is if there is a
    // malformed part header as well as an unexpected end of the form.
    parser.on('error', (error: Error) => {
      exit(error, true);
    });

    response.once('close', () => {
      released = true;

      if (map) {
        for (const upload of map.values()) {
          if (upload.file) {
            // Release resources and clean up temporary files.
            upload.file.capacitor.release();
          }
        }
      }
    });

    request.once('close', () => {
      if (!request.readableEnded)
        exit(createError(499, 'Request disconnected during file upload stream parsing.'));
    });

    request.pipe(parser as unknown as NodeJS.WritableStream);
  });
}