/*
 * Copyright 2019 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

import * as http2 from 'http2';
import { Duplex } from 'stream';

import { CallCredentials } from './call-credentials';
import { Status } from './constants';
import { EmitterAugmentation1 } from './events';
import { Filter } from './filter';
import { FilterStackFactory } from './filter-stack';
import { Metadata } from './metadata';
import { ObjectDuplex, WriteCallback } from './object-stream';
import { StreamDecoder } from './stream-decoder';
import { ChannelImplementation } from './channel';
import { Subchannel } from './subchannel';
import * as logging from './logging';
import { LogVerbosity } from './constants';

const TRACER_NAME = 'call_stream';

const {
  HTTP2_HEADER_STATUS,
  HTTP2_HEADER_CONTENT_TYPE,
  NGHTTP2_CANCEL,
} = http2.constants;

export type Deadline = Date | number;

export interface CallStreamOptions {
  deadline: Deadline;
  flags: number;
  host: string;
  parentCall: Call | null;
}

export type PartialCallStreamOptions = Partial<CallStreamOptions>;

export interface StatusObject {
  code: Status;
  details: string;
  metadata: Metadata;
}

export const enum WriteFlags {
  BufferHint = 1,
  NoCompress = 2,
  WriteThrough = 4,
}

export interface WriteObject {
  message: Buffer;
  flags?: number;
}

/**
 * This interface represents a duplex stream associated with a single gRPC call.
 */
export type Call = {
  cancelWithStatus(status: Status, details: string): void;
  getPeer(): string;
  sendMetadata(metadata: Metadata): void;

  getDeadline(): Deadline;
  getCredentials(): CallCredentials;
  setCredentials(credentials: CallCredentials): void;
  /* If the return value is null, the call has not ended yet. Otherwise, it has
   * ended with the specified status */
  getStatus(): StatusObject | null;
  getMethod(): string;
  getHost(): string;
} & EmitterAugmentation1<'metadata', Metadata> &
  EmitterAugmentation1<'status', StatusObject> &
  ObjectDuplex<WriteObject, Buffer>;

export class Http2CallStream extends Duplex implements Call {
  credentials: CallCredentials;
  filterStack: Filter;
  private http2Stream: http2.ClientHttp2Stream | null = null;
  private pendingRead = false;
  private pendingWrite: Buffer | null = null;
  private pendingWriteCallback: WriteCallback | null = null;
  private pendingFinalCallback: Function | null = null;

  private decoder = new StreamDecoder();

  private isReadFilterPending = false;
  private canPush = false;

  private unpushedReadMessages: Array<Buffer | null> = [];
  private unfilteredReadMessages: Array<Buffer | null> = [];

  // Status code mapped from :status. To be used if grpc-status is not received
  private mappedStatusCode: Status = Status.UNKNOWN;

  // Promise objects that are re-assigned to resolving promises when headers
  // or trailers received. Processing headers/trailers is asynchronous, so we
  // can use these objects to await their completion. This helps us establish
  // order of precedence when obtaining the status of the call.
  private handlingHeaders = Promise.resolve();
  private handlingTrailers = Promise.resolve();

  // This is populated (non-null) if and only if the call has ended
  private finalStatus: StatusObject | null = null;

  private subchannel: Subchannel | null = null;
  private disconnectListener: () => void;

  constructor(
    private readonly methodName: string,
    private readonly channel: ChannelImplementation,
    private readonly options: CallStreamOptions,
    filterStackFactory: FilterStackFactory,
    private readonly channelCallCredentials: CallCredentials,
    private readonly callNumber: number
  ) {
    super({ objectMode: true });
    this.filterStack = filterStackFactory.createFilter(this);
    this.credentials = channelCallCredentials;
    this.disconnectListener = () => {
      this.endCall({
        code: Status.UNAVAILABLE,
        details: 'Connection dropped',
        metadata: new Metadata(),
      });
    };
  }

  private trace(text: string): void {
    logging.trace(
      LogVerbosity.DEBUG,
      TRACER_NAME,
      '[' + this.callNumber + '] ' + text
    );
  }

  // tslint:disable-next-line:no-any
  push(chunk: any, encoding?: string): boolean {
    this.trace(
      'pushing to reader message of length ' +
        (chunk instanceof Buffer ? chunk.length : null)
    );
    return super.push(chunk);
  }

  /**
   * On first call, emits a 'status' event with the given StatusObject.
   * Subsequent calls are no-ops.
   * @param status The status of the call.
   */
  private endCall(status: StatusObject): void {
    if (this.finalStatus === null) {
      this.trace(
        'ended with status: code=' +
          status.code +
          ' details="' +
          status.details +
          '"'
      );
      this.finalStatus = status;
      /* We do this asynchronously to ensure that no async function is in the
       * call stack when we return control to the application. If an async
       * function is in the call stack, any exception thrown by the application
       * (or our tests) will bubble up and turn into promise rejection, which
       * will result in an UnhandledPromiseRejectionWarning. Because that is
       * a warning, the error will be effectively swallowed and execution will
       * continue */
      process.nextTick(() => {
        this.emit('status', status);
      });
      if (this.subchannel) {
        this.subchannel.callUnref();
        this.subchannel.removeDisconnectListener(this.disconnectListener);
      }
    }
  }

  private handleFilterError(error: Error) {
    this.cancelWithStatus(Status.INTERNAL, error.message);
  }

  private handleFilteredRead(message: Buffer) {
    /* If we the call has already ended, we don't want to do anything with
     * this message. Dropping it on the floor is correct behavior */
    if (this.finalStatus !== null) {
      return;
    }
    this.isReadFilterPending = false;
    if (this.canPush) {
      if (!this.push(message)) {
        this.canPush = false;
        (this.http2Stream as http2.ClientHttp2Stream).pause();
      }
    } else {
      this.trace(
        'unpushedReadMessages.push message of length ' + message.length
      );
      this.unpushedReadMessages.push(message);
    }
    if (this.unfilteredReadMessages.length > 0) {
      /* nextMessage is guaranteed not to be undefined because
         unfilteredReadMessages is non-empty */
      const nextMessage = this.unfilteredReadMessages.shift() as Buffer | null;
      this.filterReceivedMessage(nextMessage);
    }
  }

  private filterReceivedMessage(framedMessage: Buffer | null) {
    /* If we the call has already ended, we don't want to do anything with
     * this message. Dropping it on the floor is correct behavior */
    if (this.finalStatus !== null) {
      return;
    }
    if (framedMessage === null) {
      if (this.canPush) {
        this.push(null);
      } else {
        this.unpushedReadMessages.push(null);
      }
      return;
    }
    this.trace('filterReceivedMessage of length ' + framedMessage.length);
    this.isReadFilterPending = true;
    this.filterStack
      .receiveMessage(Promise.resolve(framedMessage))
      .then(
        this.handleFilteredRead.bind(this),
        this.handleFilterError.bind(this)
      );
  }

  private tryPush(messageBytes: Buffer | null): void {
    if (this.isReadFilterPending) {
      this.trace(
        '[' +
          this.callNumber +
          '] unfilteredReadMessages.push message of length ' +
          (messageBytes && messageBytes.length)
      );
      this.unfilteredReadMessages.push(messageBytes);
    } else {
      this.filterReceivedMessage(messageBytes);
    }
  }

  private handleTrailers(headers: http2.IncomingHttpHeaders) {
    this.trace('received HTTP/2 trailing headers frame');
    const code: Status = this.mappedStatusCode;
    const details = '';
    let metadata: Metadata;
    try {
      metadata = Metadata.fromHttp2Headers(headers);
    } catch (e) {
      metadata = new Metadata();
    }
    const status: StatusObject = { code, details, metadata };
    this.handlingTrailers = (async () => {
      let finalStatus;
      try {
        // Attempt to assign final status.
        finalStatus = await this.filterStack.receiveTrailers(
          Promise.resolve(status)
        );
      } catch (error) {
        await this.handlingHeaders;
        // This is a no-op if the call was already ended when handling headers.
        this.endCall({
          code: Status.INTERNAL,
          details: 'Failed to process received status',
          metadata: new Metadata(),
        });
        return;
      }
      // It's possible that headers were received but not fully handled yet.
      // Give the headers handler an opportunity to end the call first,
      // if an error occurred.
      await this.handlingHeaders;
      // This is a no-op if the call was already ended when handling headers.
      this.endCall(finalStatus);
    })();
  }

  attachHttp2Stream(
    stream: http2.ClientHttp2Stream,
    subchannel: Subchannel
  ): void {
    if (this.finalStatus !== null) {
      stream.close(NGHTTP2_CANCEL);
    } else {
      this.trace(
        'attachHttp2Stream from subchannel ' + subchannel.getAddress()
      );
      this.http2Stream = stream;
      this.subchannel = subchannel;
      subchannel.addDisconnectListener(this.disconnectListener);
      subchannel.callRef();
      stream.on('response', (headers, flags) => {
        this.trace('received HTTP/2 headers frame');
        switch (headers[':status']) {
          // TODO(murgatroid99): handle 100 and 101
          case 400:
            this.mappedStatusCode = Status.INTERNAL;
            break;
          case 401:
            this.mappedStatusCode = Status.UNAUTHENTICATED;
            break;
          case 403:
            this.mappedStatusCode = Status.PERMISSION_DENIED;
            break;
          case 404:
            this.mappedStatusCode = Status.UNIMPLEMENTED;
            break;
          case 429:
          case 502:
          case 503:
          case 504:
            this.mappedStatusCode = Status.UNAVAILABLE;
            break;
          default:
            this.mappedStatusCode = Status.UNKNOWN;
        }

        if (flags & http2.constants.NGHTTP2_FLAG_END_STREAM) {
          this.handleTrailers(headers);
        } else {
          let metadata: Metadata;
          try {
            metadata = Metadata.fromHttp2Headers(headers);
          } catch (error) {
            this.endCall({
              code: Status.UNKNOWN,
              details: error.message,
              metadata: new Metadata(),
            });
            return;
          }
          this.handlingHeaders = this.filterStack
            .receiveMetadata(Promise.resolve(metadata))
            .then(finalMetadata => {
              this.emit('metadata', finalMetadata);
            })
            .catch(error => {
              this.destroyHttp2Stream();
              this.endCall({
                code: Status.UNKNOWN,
                details: error.message,
                metadata: new Metadata(),
              });
            });
        }
      });
      stream.on('trailers', this.handleTrailers.bind(this));
      stream.on('data', (data: Buffer) => {
        this.trace('receive HTTP/2 data frame of length ' + data.length);
        const messages = this.decoder.write(data);

        for (const message of messages) {
          this.trace('parsed message of length ' + message.length);
          this.tryPush(message);
        }
      });
      stream.on('end', () => {
        this.trace('received HTTP/2 end of data flag');
        this.tryPush(null);
      });
      stream.on('close', async () => {
        this.trace('HTTP/2 stream closed with code ' + stream.rstCode);
        let code: Status;
        let details = '';
        switch (stream.rstCode) {
          case http2.constants.NGHTTP2_REFUSED_STREAM:
            code = Status.UNAVAILABLE;
            details = 'Stream refused by server';
            break;
          case http2.constants.NGHTTP2_CANCEL:
            code = Status.CANCELLED;
            details = 'Call cancelled';
            break;
          case http2.constants.NGHTTP2_ENHANCE_YOUR_CALM:
            code = Status.RESOURCE_EXHAUSTED;
            details = 'Bandwidth exhausted';
            break;
          case http2.constants.NGHTTP2_INADEQUATE_SECURITY:
            code = Status.PERMISSION_DENIED;
            details = 'Protocol not secure enough';
            break;
          default:
            code = Status.INTERNAL;
        }
        // This guarantees that if trailers were received, the value of the
        // 'grpc-status' header takes precedence for emitted status data.
        await this.handlingTrailers;
        // This is a no-op if trailers were received at all.
        // This is OK, because status codes emitted here correspond to more
        // catastrophic issues that prevent us from receiving trailers in the
        // first place.
        this.endCall({ code, details, metadata: new Metadata() });
      });
      stream.on('error', (err: Error) => {
        /* We need an error handler here to stop "Uncaught Error" exceptions
         * from bubbling up. However, errors here should all correspond to
         * "close" events, where we will handle the error more granularly */
      });
      if (!this.pendingRead) {
        stream.pause();
      }
      if (this.pendingWrite) {
        if (!this.pendingWriteCallback) {
          throw new Error('Invalid state in write handling code');
        }
        stream.write(this.pendingWrite, this.pendingWriteCallback);
      }
      if (this.pendingFinalCallback) {
        this.trace('calling end() on HTTP/2 stream');
        stream.end(this.pendingFinalCallback);
      }
    }
  }

  sendMetadata(metadata: Metadata): void {
    this.trace('Sending metadata');
    this.channel._startCallStream(this, metadata);
  }

  private destroyHttp2Stream() {
    // The http2 stream could already have been destroyed if cancelWithStatus
    // is called in response to an internal http2 error.
    if (this.http2Stream !== null && !this.http2Stream.destroyed) {
      /* TODO(murgatroid99): Determine if we want to send different RST_STREAM
       * codes based on the status code */
      this.http2Stream.close(NGHTTP2_CANCEL);
    }
  }

  cancelWithStatus(status: Status, details: string): void {
    this.destroyHttp2Stream();
    (async () => {
      // If trailers are currently being processed, the call should be ended
      // by handleTrailers instead.
      await this.handlingTrailers;
      this.endCall({ code: status, details, metadata: new Metadata() });
    })();
  }

  getDeadline(): Deadline {
    return this.options.deadline;
  }

  getCredentials(): CallCredentials {
    return this.credentials;
  }

  setCredentials(credentials: CallCredentials): void {
    this.credentials = this.channelCallCredentials.compose(credentials);
  }

  getStatus(): StatusObject | null {
    return this.finalStatus;
  }

  getPeer(): string {
    throw new Error('Not yet implemented');
  }

  getMethod(): string {
    return this.methodName;
  }

  getHost(): string {
    return this.options.host;
  }

  _read(size: number) {
    /* If we have already emitted a status, we should not emit any more
     * messages and we should communicate that the stream has ended */
    if (this.finalStatus !== null) {
      this.push(null);
      return;
    }
    this.canPush = true;
    if (this.http2Stream === null) {
      this.pendingRead = true;
    } else {
      while (this.unpushedReadMessages.length > 0) {
        const nextMessage = this.unpushedReadMessages.shift();
        this.canPush = this.push(nextMessage);
        if (nextMessage === null || !this.canPush) {
          this.canPush = false;
          return;
        }
      }
      /* Only resume reading from the http2Stream if we don't have any pending
       * messages to emit, and we haven't gotten the signal to stop pushing
       * messages */
      this.http2Stream.resume();
    }
  }

  _write(chunk: WriteObject, encoding: string, cb: WriteCallback) {
    this.trace('write() called with message of length ' + chunk.message.length);
    this.filterStack.sendMessage(Promise.resolve(chunk)).then(message => {
      if (this.http2Stream === null) {
        this.pendingWrite = message.message;
        this.pendingWriteCallback = cb;
      } else {
        this.http2Stream.write(message.message, cb);
      }
    }, this.handleFilterError.bind(this));
  }

  _final(cb: Function) {
    this.trace('end() called');
    if (this.http2Stream === null) {
      this.pendingFinalCallback = cb;
    } else {
      this.trace('calling end() on HTTP/2 stream');
      this.http2Stream.end(cb);
    }
  }
}