import { Server, IncomingMessage, ServerResponse, OutgoingHttpHeaders } from 'http';
import { HttpRequestHandler, mixed, Middleware } from '../../interfaces';
import {
  subscribe as graphqlSubscribe,
  ExecutionResult,
  ExecutionArgs,
  specifiedRules,
  validate,
  GraphQLError,
  parse,
  DocumentNode,
  execute,
  getOperationAST,
} from 'graphql';
import * as WebSocket from 'ws';
import { SubscriptionServer, ConnectionContext, ExecutionParams } from 'subscriptions-transport-ws';
import { GRAPHQL_TRANSPORT_WS_PROTOCOL } from 'graphql-ws';
import { useServer } from 'graphql-ws/lib/use/ws';
import parseUrl = require('parseurl');
import { pluginHookFromOptions } from '../pluginHook';
import { isEmpty } from './createPostGraphileHttpRequestHandler';
import { makeLiveSubscribe } from './liveSubscribe';

interface Deferred<T> extends Promise<T> {
  resolve: (input?: T | PromiseLike<T> | undefined) => void;
  reject: (error: Error) => void;
}

function lowerCaseKeys(obj: Record<string, any>): Record<string, any> {
  return Object.keys(obj).reduce((memo, key) => {
    memo[key.toLowerCase()] = obj[key];
    return memo;
  }, {});
}

function deferred<T = void>(): Deferred<T> {
  let resolve: (input?: T | PromiseLike<T> | undefined) => void;
  let reject: (error: Error) => void;
  const promise = new Promise<T>((_resolve, _reject): void => {
    resolve = _resolve;
    reject = _reject;
  });
  // tslint:disable-next-line prefer-object-spread
  return Object.assign(promise, {
    // @ts-ignore This isn't used before being defined.
    resolve,
    // @ts-ignore This isn't used before being defined.
    reject,
  });
}

export async function enhanceHttpServerWithWebSockets<
  Request extends IncomingMessage = IncomingMessage,
  Response extends ServerResponse = ServerResponse
>(
  websocketServer: Server,
  postgraphileMiddleware: HttpRequestHandler,
  subscriptionServerOptions?: {
    keepAlive?: number;
    graphqlRoute?: string;
  },
): Promise<void> {
  if (websocketServer['__postgraphileSubscriptionsEnabled']) {
    return;
  }
  websocketServer['__postgraphileSubscriptionsEnabled'] = true;
  const {
    options,
    getGraphQLSchema,
    withPostGraphileContextFromReqRes,
    handleErrors,
  } = postgraphileMiddleware;
  const pluginHook = pluginHookFromOptions(options);
  const liveSubscribe = makeLiveSubscribe({ pluginHook, options });
  const graphqlRoute =
    (subscriptionServerOptions && subscriptionServerOptions.graphqlRoute) ||
    (options.externalUrlBase || '') + (options.graphqlRoute || '/graphql');
  const { subscriptions, live, websockets = subscriptions || live ? ['v0', 'v1'] : [] } = options;

  // enhance with WebSockets shouldnt be called if there are no websocket versions
  if (!websockets?.length) {
    throw new Error(`Invalid value for \`websockets\` option: '${JSON.stringify(websockets)}'`);
  }

  const schema = await getGraphQLSchema();

  const keepalivePromisesByContextKey: { [contextKey: string]: Deferred<void> } = {};

  // IMPORTANT: if you change this, be sure to change `releaseAllContextsForSocket` too
  const contextKey = (ws: WebSocket, opId: string): string => ws['postgraphileId'] + '|' + opId;

  const releaseAllContextsForSocket = (ws: WebSocket): void => {
    const prefix = ws['postgraphileId'] + '|';
    for (const [key, promise] of Object.entries(keepalivePromisesByContextKey)) {
      if (key.startsWith(prefix)) {
        promise.resolve();
        delete keepalivePromisesByContextKey[key];
      }
    }
  };

  const releaseContextForSocketAndOpId = (ws: WebSocket, opId: string): void => {
    const promise = keepalivePromisesByContextKey[contextKey(ws, opId)];
    if (promise) {
      promise.resolve();
      delete keepalivePromisesByContextKey[contextKey(ws, opId)];
    }
  };

  const addContextForSocketAndOpId = (
    context: mixed,
    ws: WebSocket,
    opId: string,
  ): Deferred<void> => {
    releaseContextForSocketAndOpId(ws, opId);
    const promise = deferred();
    promise['context'] = context;
    keepalivePromisesByContextKey[contextKey(ws, opId)] = promise;
    return promise;
  };

  const applyMiddleware = async (
    middlewares: Array<Middleware<Request, Response>> = [],
    req: Request,
    res: Response,
  ): Promise<void> => {
    for (const middleware of middlewares) {
      // TODO: add Koa support
      await new Promise<void>((resolve, reject): void => {
        middleware(req, res, err => (err ? reject(err) : resolve()));
      });
    }
  };

  const reqResFromSocket = async (
    socket: WebSocket,
  ): Promise<{
    req: Request;
    res: Response;
  }> => {
    const req = socket['__postgraphileReq'];
    if (!req) {
      throw new Error('req could not be extracted');
    }
    let dummyRes: Response | undefined = socket['__postgraphileRes'];
    if (req.res) {
      throw new Error(
        "Please get in touch with Benjie; we weren't expecting req.res to be present but we want to reserve it for future usage.",
      );
    }
    if (!dummyRes) {
      dummyRes = new ServerResponse(req) as Response;
      dummyRes.writeHead = (
        statusCode: number,
        _statusMessage?: OutgoingHttpHeaders | string | undefined,
        headers?: OutgoingHttpHeaders | undefined,
      ): Response => {
        if (statusCode && statusCode > 200) {
          // tslint:disable-next-line no-console
          console.error(
            `Something used 'writeHead' to write a '${statusCode}' error for websockets - check the middleware you're passing!`,
          );
          socket.close();
        } else if (headers) {
          // tslint:disable-next-line no-console
          console.error(
            "Passing headers to 'writeHead' is not supported with websockets currently - check the middleware you're passing",
          );
          socket.close();
        }
        return dummyRes!;
      };
      await applyMiddleware(options.websocketMiddlewares, req, dummyRes);

      // reqResFromSocket is only called once per socket, so there's no race condition here
      // eslint-disable-next-line require-atomic-updates
      socket['__postgraphileRes'] = dummyRes;
    }
    return { req, res: dummyRes };
  };

  const getContext = (socket: WebSocket, opId: string, isSubscription: boolean): Promise<mixed> => {
    const singleStatement = isSubscription;
    return new Promise((resolve, reject): void => {
      reqResFromSocket(socket)
        .then(({ req, res }) =>
          withPostGraphileContextFromReqRes(req, res, { singleStatement }, context => {
            const promise = addContextForSocketAndOpId(context, socket, opId);
            resolve(promise['context']);
            return promise;
          }),
        )
        .then(null, reject);
    });
  };

  const staticValidationRules = pluginHook('postgraphile:validationRules:static', specifiedRules, {
    options,
  });

  let socketId = 0;

  let v0Wss: WebSocket.Server | null = null;
  if (websockets.includes('v0')) {
    v0Wss = new WebSocket.Server({ noServer: true });
    SubscriptionServer.create(
      {
        schema,
        validationRules: staticValidationRules,
        execute:
          options.websocketOperations === 'all'
            ? execute
            : () => {
                throw new Error('Only subscriptions are allowed over websocket transport');
              },
        subscribe: options.live ? liveSubscribe : graphqlSubscribe,
        onConnect(
          connectionParams: Record<string, any>,
          _socket: WebSocket,
          connectionContext: ConnectionContext,
        ) {
          const { socket, request } = connectionContext;
          socket['postgraphileId'] = ++socketId;
          if (!request) {
            throw new Error('No request!');
          }
          const normalizedConnectionParams = lowerCaseKeys(connectionParams);
          request['connectionParams'] = connectionParams;
          request['normalizedConnectionParams'] = normalizedConnectionParams;
          socket['__postgraphileReq'] = request;
          if (!request.headers.authorization && normalizedConnectionParams['authorization']) {
            /*
             * Enable JWT support through connectionParams.
             *
             * For other headers you'll need to do this yourself for security
             * reasons (e.g. we don't want to allow overriding of Origin /
             * Referer / etc)
             */
            request.headers.authorization = String(normalizedConnectionParams['authorization']);
          }

          socket['postgraphileHeaders'] = {
            ...normalizedConnectionParams,
            // The original headers must win (for security)
            ...request.headers,
          };
        },
        // tslint:disable-next-line no-any
        async onOperation(message: any, params: ExecutionParams, socket: WebSocket) {
          const opId = message.id;

          // Override schema (for --watch)
          params.schema = await getGraphQLSchema();

          const { req, res } = await reqResFromSocket(socket);
          const meta = {};
          const formatResponse = <TExecutionResult extends ExecutionResult = ExecutionResult>(
            response: TExecutionResult,
          ): TExecutionResult => {
            if (response.errors) {
              response.errors = handleErrors(response.errors, req, res);
            }
            if (!isEmpty(meta)) {
              response['meta'] = meta;
            }

            return response;
          };
          // onOperation is only called once per params object, so there's no race condition here
          // eslint-disable-next-line require-atomic-updates
          params.formatResponse = formatResponse;
          const hookedParams = pluginHook
            ? pluginHook('postgraphile:ws:onOperation', params, {
                message,
                params,
                socket,
                options,
              })
            : params;
          const finalParams: typeof hookedParams & { query: DocumentNode } = {
            ...hookedParams,
            query:
              typeof hookedParams.query !== 'string'
                ? hookedParams.query
                : parse(hookedParams.query),
          };
          if (!finalParams.query) {
            return Promise.reject(new Error('Must provide document'));
          }

          const operation = getOperationAST(finalParams.query, finalParams.operationName);
          if (!operation) {
            return Promise.reject(new Error('Unable to identify operation'));
          }
          const isSubscription = operation.operation === 'subscription';

          // We used to call `getContext` here, now we just persist this side effect instead.
          await reqResFromSocket(socket);

          // You are strongly encouraged to use
          // `postgraphile:validationRules:static` if possible - you should
          // only use this one if you need access to variables.
          const moreValidationRules = pluginHook('postgraphile:validationRules', [], {
            options,
            req,
            res,
            variables: params.variables,
            operationName: params.operationName,
            meta,
          });
          if (moreValidationRules.length) {
            const validationErrors: ReadonlyArray<GraphQLError> = validate(
              params.schema,
              finalParams.query,
              moreValidationRules,
            );
            if (validationErrors.length) {
              const error = new Error(
                'Query validation failed: \n' + validationErrors.map(e => e.message).join('\n'),
              );
              error['errors'] = validationErrors;
              return Promise.reject(error);
            }
          }

          const context = await getContext(socket, opId, isSubscription);
          Object.assign(params.context, context);

          return finalParams;
        },
        onOperationComplete(socket: WebSocket, opId: string) {
          releaseContextForSocketAndOpId(socket, opId);
        },
        onDisconnect(socket: WebSocket) {
          releaseAllContextsForSocket(socket);
        },

        /*
         * Heroku times out after 55s:
         *   https://devcenter.heroku.com/articles/error-codes#h15-idle-connection
         *
         * The subscriptions-transport-ws client times out by default 30s after last keepalive:
         *   https://github.com/apollographql/subscriptions-transport-ws/blob/52758bfba6190169a28078ecbafd2e457a2ff7a8/src/defaults.ts#L1
         *
         * GraphQL Playground times out after 20s:
         *   https://github.com/prisma/graphql-playground/blob/fa91e1b6d0488e6b5563d8b472682fe728ee0431/packages/graphql-playground-react/src/state/sessions/fetchingSagas.ts#L81
         *
         * Pick a number under these ceilings.
         */
        keepAlive: 15000,
        ...subscriptionServerOptions,
      },
      v0Wss,
    );
  }

  let v1Wss: WebSocket.Server | null = null;
  if (websockets.includes('v1')) {
    v1Wss = new WebSocket.Server({ noServer: true });
    useServer(
      {
        schema,
        execute:
          options.websocketOperations === 'all'
            ? execute
            : () => {
                throw new Error('Only subscriptions are allowed over WebSocket transport');
              },
        subscribe: options.live ? liveSubscribe : graphqlSubscribe,
        onConnect(ctx) {
          const { socket, request } = ctx.extra;
          socket['postgraphileId'] = ++socketId;
          socket['__postgraphileReq'] = request;

          const normalizedConnectionParams = lowerCaseKeys(ctx.connectionParams || {});
          request['connectionParams'] = ctx.connectionParams || {};
          request['normalizedConnectionParams'] = normalizedConnectionParams;

          if (!request.headers.authorization && normalizedConnectionParams['authorization']) {
            /*
             * Enable JWT support through connectionParams.
             *
             * For other headers you'll need to do this yourself for security
             * reasons (e.g. we don't want to allow overriding of Origin /
             * Referer / etc)
             */
            request.headers.authorization = String(normalizedConnectionParams['authorization']);
          }

          socket['postgraphileHeaders'] = {
            ...normalizedConnectionParams,
            // The original headers must win (for security)
            ...request.headers,
          };
        },
        async onSubscribe(ctx, msg) {
          // Override schema (for --watch)
          const schema = await getGraphQLSchema();

          const { payload } = msg;
          const args = {
            schema,
            contextValue: {},
            operationName: payload.operationName,
            document: payload.query ? parse(payload.query) : null, // parse if there is something to parse
            variableValues: payload.variables,
          };

          // for supplying custom execution arguments. if not already
          // complete, the pluginHook should fill in the gaps
          const hookedArgs = (pluginHook
            ? pluginHook('postgraphile:ws:onSubscribe', args, {
                context: ctx,
                message: msg,
                options,
              })
            : args) as ExecutionArgs;
          if (!args.document) {
            return [
              // same error that graphql.validate would throw if the document is missing
              new GraphQLError('Must provide document'),
            ];
          }

          const operation = getOperationAST(args.document, hookedArgs.operationName);
          if (!operation) {
            return [new GraphQLError('Unable to identify operation')];
          }
          const isSubscription = operation.operation === 'subscription';

          // We used to call `getContext` here, now we just persist this side effect instead.
          await reqResFromSocket(ctx.extra.socket);

          // when supplying custom execution args from the
          // onSubscribe, you're trusted to do the validation
          const validationErrors = validate(
            hookedArgs.schema,
            hookedArgs.document,
            staticValidationRules,
          );
          if (validationErrors.length) {
            return validationErrors;
          }

          // You are strongly encouraged to use
          // `postgraphile:validationRules:static` if possible - you should
          // only use this one if you need access to variables.
          const { req, res } = await reqResFromSocket(ctx.extra.socket);
          const moreValidationRules = pluginHook('postgraphile:validationRules', [], {
            options,
            req,
            res,
            variables: hookedArgs.variableValues,
            operationName: hookedArgs.operationName,
            // no meta because validation errors returned from here will be
            // served through the error message. it contains just the GraphQLErrors
            // (there is no result to add the meta to)
          });
          if (moreValidationRules.length) {
            const moreValidationErrors = validate(
              hookedArgs.schema,
              hookedArgs.document,
              moreValidationRules,
            );
            if (moreValidationErrors.length) {
              return moreValidationErrors;
            }
          }

          const context = await getContext(ctx.extra.socket, msg.id, isSubscription);
          Object.assign(hookedArgs.contextValue, context);

          return hookedArgs;
        },
        async onError(ctx, msg, errors) {
          // errors returned from onSubscribe
          releaseContextForSocketAndOpId(ctx.extra.socket, msg.id);
          const { req, res } = await reqResFromSocket(ctx.extra.socket);
          return handleErrors(errors, req, res);
        },
        async onNext(ctx, _msg, _args, result) {
          if (result.errors) {
            // operation execution errors
            const { req, res } = await reqResFromSocket(ctx.extra.socket);
            result.errors = handleErrors(result.errors, req, res);
            return result;
          }
        },
        onComplete(ctx, msg) {
          releaseContextForSocketAndOpId(ctx.extra.socket, msg.id);
        },
        onClose(ctx) {
          releaseAllContextsForSocket(ctx.extra.socket);
        },
      },
      v1Wss,
      /*
       * Heroku times out after 55s:
       *   https://devcenter.heroku.com/articles/error-codes#h15-idle-connection
       *
       * GraphQL Playground times out after 20s:
       *   https://github.com/prisma/graphql-playground/blob/fa91e1b6d0488e6b5563d8b472682fe728ee0431/packages/graphql-playground-react/src/state/sessions/fetchingSagas.ts#L81
       *
       * Pick a number under these ceilings.
       */
      subscriptionServerOptions?.keepAlive, // default is 12 seconds
    );
  }

  // listen for upgrades and delegate requests according to the WS subprotocol
  websocketServer.on('upgrade', (req: IncomingMessage, socket, head) => {
    const { pathname = '' } = parseUrl(req) || {};
    const isGraphqlRoute = pathname === graphqlRoute;
    if (isGraphqlRoute) {
      const protocol = req.headers['sec-websocket-protocol'];
      const protocols = Array.isArray(protocol)
        ? protocol
        : protocol?.split(',').map(p => p.trim());

      const wss =
        v0Wss &&
        protocols?.includes('graphql-ws') &&
        !protocols.includes(GRAPHQL_TRANSPORT_WS_PROTOCOL)
          ? v0Wss
          : // v1 will welcome its own subprotocol `graphql-transport-ws`
            // and gracefully reject invalid ones. if the client supports
            // both v0 and v1, v1 will prevail
            v1Wss;
      if (wss) {
        wss.handleUpgrade(req, socket as any, head, ws => {
          wss.emit('connection', ws, req);
        });
      }
    }
  });
}