/*
 * Copyright 2021 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 protoLoader from '@grpc/proto-loader';
import { experimental, logVerbosity, StatusObject } from "@grpc/grpc-js";
import { Listener__Output } from '../generated/envoy/config/listener/v3/Listener';
import { RdsState } from "./rds-state";
import { Watcher, XdsStreamState } from "./xds-stream-state";
import { HttpConnectionManager__Output } from '../generated/envoy/extensions/filters/network/http_connection_manager/v3/HttpConnectionManager';
import { decodeSingleResource, HTTP_CONNECTION_MANGER_TYPE_URL_V2, HTTP_CONNECTION_MANGER_TYPE_URL_V3 } from '../resources';
import { getTopLevelFilterUrl, validateTopLevelFilter } from '../http-filter';
import { EXPERIMENTAL_FAULT_INJECTION } from '../environment';

const TRACER_NAME = 'xds_client';

function trace(text: string): void {
  experimental.trace(logVerbosity.DEBUG, TRACER_NAME, text);
}

const ROUTER_FILTER_URL = 'type.googleapis.com/envoy.extensions.filters.http.router.v3.Router';

export class LdsState implements XdsStreamState<Listener__Output> {
  versionInfo = '';
  nonce = '';

  private watchers: Map<string, Watcher<Listener__Output>[]> = new Map<string, Watcher<Listener__Output>[]>();
  private latestResponses: Listener__Output[] = [];
  private latestIsV2 = false;

  constructor(private rdsState: RdsState, private updateResourceNames: () => void) {}

  addWatcher(targetName: string, watcher: Watcher<Listener__Output>) {
    trace('Adding RDS watcher for targetName ' + targetName);
    let watchersEntry = this.watchers.get(targetName);
    let addedServiceName = false;
    if (watchersEntry === undefined) {
      addedServiceName = true;
      watchersEntry = [];
      this.watchers.set(targetName, watchersEntry);
    }
    watchersEntry.push(watcher);

    /* If we have already received an update for the requested edsServiceName,
     * immediately pass that update along to the watcher */
    const isV2 = this.latestIsV2;
    for (const message of this.latestResponses) {
      if (message.name === targetName) {
        /* These updates normally occur asynchronously, so we ensure that
         * the same happens here */
        process.nextTick(() => {
          trace('Reporting existing RDS update for new watcher for targetName ' + targetName);
          watcher.onValidUpdate(message, isV2);
        });
      }
    }
    if (addedServiceName) {
      this.updateResourceNames();
    }
  }

  removeWatcher(targetName: string, watcher: Watcher<Listener__Output>): void {
    trace('Removing RDS watcher for targetName ' + targetName);
    const watchersEntry = this.watchers.get(targetName);
    let removedServiceName = false;
    if (watchersEntry !== undefined) {
      const entryIndex = watchersEntry.indexOf(watcher);
      if (entryIndex >= 0) {
        watchersEntry.splice(entryIndex, 1);
      }
      if (watchersEntry.length === 0) {
        removedServiceName = true;
        this.watchers.delete(targetName);
      }
    }
    if (removedServiceName) {
      this.updateResourceNames();
    }
  }

  getResourceNames(): string[] {
    return Array.from(this.watchers.keys());
  }

  private validateResponse(message: Listener__Output, isV2: boolean): boolean {
    if (
      !(
        message.api_listener?.api_listener &&
        (message.api_listener.api_listener.type_url === HTTP_CONNECTION_MANGER_TYPE_URL_V2 ||
          message.api_listener.api_listener.type_url === HTTP_CONNECTION_MANGER_TYPE_URL_V3)
      )
    ) {
      return false;
    }
    const httpConnectionManager = decodeSingleResource(HTTP_CONNECTION_MANGER_TYPE_URL_V3, message.api_listener!.api_listener.value);
    if (!isV2 && EXPERIMENTAL_FAULT_INJECTION) {
      const filterNames = new Set<string>();
      for (const [index, httpFilter] of httpConnectionManager.http_filters.entries()) {
        if (filterNames.has(httpFilter.name)) {
          trace('LDS response validation failed: duplicate HTTP filter name ' + httpFilter.name);
          return false;
        }
        filterNames.add(httpFilter.name);
        if (!validateTopLevelFilter(httpFilter)) {
          trace('LDS response validation failed: ' + httpFilter.name + ' filter validation failed');
          return false;
        }
        /* Validate that the last filter, and only the last filter, is the
         * router filter. */
        const filterUrl = getTopLevelFilterUrl(httpFilter.typed_config!)
        if (index < httpConnectionManager.http_filters.length - 1) {
          if (filterUrl === ROUTER_FILTER_URL) {
            trace('LDS response validation failed: router filter is before end of list');
            return false;
          }
        } else {
          if (filterUrl !== ROUTER_FILTER_URL) {
            trace('LDS response validation failed: final filter is ' + filterUrl);
            return false;
          }
        }
      }
    }
    switch (httpConnectionManager.route_specifier) {
      case 'rds':
        return !!httpConnectionManager.rds?.config_source?.ads;
      case 'route_config':
        return this.rdsState.validateResponse(httpConnectionManager.route_config!, isV2);
    }
    return false;
  }

  private handleMissingNames(allTargetNames: Set<string>) {
    for (const [targetName, watcherList] of this.watchers.entries()) {
      if (!allTargetNames.has(targetName)) {
        for (const watcher of watcherList) {
          watcher.onResourceDoesNotExist();
        }
      }
    }
  }

  handleResponses(responses: Listener__Output[], isV2: boolean): string | null {
    for (const message of responses) {
      if (!this.validateResponse(message, isV2)) {
        trace('LDS validation failed for message ' + JSON.stringify(message));
        return 'LDS Error: Route validation failed';
      }
    }
    this.latestResponses = responses;
    this.latestIsV2 = isV2;
    const allTargetNames = new Set<string>();
    const allRouteConfigNames = new Set<string>();
    for (const message of responses) {
      allTargetNames.add(message.name);
      const httpConnectionManager = decodeSingleResource(HTTP_CONNECTION_MANGER_TYPE_URL_V3, message.api_listener!.api_listener!.value);
      if (httpConnectionManager.rds) {
        allRouteConfigNames.add(httpConnectionManager.rds.route_config_name);
      }
      const watchers = this.watchers.get(message.name) ?? [];
      for (const watcher of watchers) {
        watcher.onValidUpdate(message, isV2);
      }
    }
    trace('Received RDS response with route config names ' + Array.from(allTargetNames));
    this.handleMissingNames(allTargetNames);
    this.rdsState.handleMissingNames(allRouteConfigNames);
    return null;
  }

  reportStreamError(status: StatusObject): void {
    for (const watcherList of this.watchers.values()) {
      for (const watcher of watcherList) {
        watcher.onTransientError(status);
      }
    }
  }
}