/*
 * 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 { CallCredentials } from './call-credentials';
import { Status } from './constants';
import { Filter } from './filter';
import { FilterStackFactory } from './filter-stack';
import { Metadata } from './metadata';
import { StreamDecoder } from './stream-decoder';
import { ChannelImplementation } from './channel';
import { Subchannel } from './subchannel';

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;
}

export interface MetadataListener {
  (metadata: Metadata, next: (metadata: Metadata) => void): void;
}

export interface MessageListener {
  (message: any, next: (message: any) => void): void;
}

export interface StatusListener {
  (status: StatusObject, next: (status: StatusObject) => void): void;
}

export interface FullListener {
  onReceiveMetadata: MetadataListener;
  onReceiveMessage: MessageListener;
  onReceiveStatus: StatusListener;
}

export type Listener = Partial<FullListener>;

export interface InterceptingListener {
  onReceiveMetadata(metadata: Metadata): void;
  onReceiveMessage(message: any): void;
  onReceiveStatus(status: StatusObject): void;
}

class InterceptingListenerImpl implements InterceptingListener {
  constructor(private listener: FullListener, private nextListener: InterceptingListener) {}

  onReceiveMetadata(metadata: Metadata): void {
    const next = this.nextListener.onReceiveMetadata.bind(this.nextListener);
    this.listener.onReceiveMetadata(metadata, next);
  }
  onReceiveMessage(message: any): void {
    const next = this.nextListener.onReceiveMessage.bind(this.nextListener);
    this.listener.onReceiveMessage(message, next);
  }
  onReceiveStatus(status: StatusObject): void {
    const next = this.nextListener.onReceiveStatus.bind(this.nextListener);
    this.listener.onReceiveStatus(status, next);
  }
}

export interface WriteCallback {
  (error?: Error | null): void;
}

export type Call = {
  cancelWithStatus(status: Status, details: string): void;
  getPeer(): string;
  start(metadata: Metadata, listener: InterceptingListener): void;
  write(writeObj: WriteObject, callback: WriteCallback): void;
  startRead(): void;
  halfClose(): void;

  getDeadline(): Deadline;
  getCredentials(): CallCredentials;
  setCredentials(credentials: CallCredentials): void;
  getMethod(): string;
  getHost(): string;
}

export class Http2CallStream 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 writesClosed = false;

  private decoder = new StreamDecoder();

  private isReadFilterPending = false;
  private canPush = false;
  private readsClosed = false;

  private statusOutput = 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;

  // 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;

  private listener: InterceptingListener | null = null;

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

  private outputStatus() {
    /* Precondition: this.finalStatus !== null */
    if (!this.statusOutput) {
      this.statusOutput = true;
      /* 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.listener!.onReceiveStatus(this.finalStatus!);
      });
      if (this.subchannel) {
        this.subchannel.callUnref();
        this.subchannel.removeDisconnectListener(this.disconnectListener);
      }
    }
  }

  /**
   * 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 the status is OK and a new status comes in (e.g. from a
     * deserialization failure), that new status takes priority */
    if (this.finalStatus === null || this.finalStatus.code === Status.OK) {
      this.finalStatus = status;
      /* Then, if an incoming message is still being handled or the status code
       * is OK, hold off on emitting the status until that is done */
      if (this.readsClosed || this.finalStatus.code !== Status.OK) {
        this.outputStatus();
      }
    }
  }

  private push(message: Buffer | null): void {
    if (message === null) {
      this.readsClosed = true;
      if (this.finalStatus) {
        this.outputStatus();
      }
    } else {
      this.listener!.onReceiveMessage(message);
    }
  }

  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) {
      this.push(null);
      return;
    }
    this.isReadFilterPending = false;
    if (this.canPush) {
      this.push(message)
      this.canPush = false;
      this.http2Stream!.pause();
    } else {
      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) {
      this.push(null);
      return;
    }
    if (framedMessage === null) {
      if (this.canPush) {
        this.push(null);
      } else {
        this.unpushedReadMessages.push(null);
      }
      return;
    }
    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.unfilteredReadMessages.push(messageBytes);
    } else {
      this.filterReceivedMessage(messageBytes);
    }
  }

  private handleTrailers(headers: http2.IncomingHttpHeaders) {
    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 };
    let finalStatus;
    try {
      // Attempt to assign final status.
      finalStatus = this.filterStack.receiveTrailers(status);
    } catch (error) {
      // 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;
    }
    // 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.http2Stream = stream;
      this.subchannel = subchannel;
      subchannel.addDisconnectListener(this.disconnectListener);
      subchannel.callRef();
      stream.on('response', (headers, flags) => {
        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;
          }
          try {
            const finalMetadata = this.filterStack.receiveMetadata(metadata);
            this.listener!.onReceiveMetadata(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) => {
        const messages = this.decoder.write(data);

        for (const message of messages) {
          this.tryPush(message);
        }
      });
      stream.on('end', () => {
        this.tryPush(null);
      });
      stream.on('close', async () => {
        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 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.writesClosed) {
        stream.end();
      }
    }
  }

  start(metadata: Metadata, listener: InterceptingListener) {
    this.listener = listener;
    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();
    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;
  }

  startRead() {
    /* 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 {
      if (this.unpushedReadMessages.length > 0) {
        const nextMessage: Buffer | null = this.unpushedReadMessages.shift() as Buffer | null;
        this.push(nextMessage);
        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(writeObj: WriteObject, cb: WriteCallback) {
    this.filterStack.sendMessage(Promise.resolve(writeObj)).then(message => {
      if (this.http2Stream === null) {
        this.pendingWrite = message.message;
        this.pendingWriteCallback = cb;
      } else {
        this.http2Stream.write(message.message, cb);
      }
    }, this.handleFilterError.bind(this));
  }

  halfClose() {
    this.writesClosed = true;
    if (this.http2Stream !== null) {
      this.http2Stream.end();
    }
  }
}