import * as gcpMetadata from 'gcp-metadata';
import {OutgoingHttpHeaders} from 'http';
import * as os from 'os';

import {Constants} from './constants';
import {Logger} from './logger';
import {SpanKind, Trace} from './trace';
import {TraceLabels} from './trace-labels';
import {Singleton} from './util';
import {
  DecorateRequestOptions,
  GoogleAuthOptions,
  Service,
} from '@google-cloud/common';

// eslint-disable-next-line @typescript-eslint/no-var-requires
const pjson = require('../../package.json');

// TODO(kjin): This value should be exported from @g-c/c.
const NO_PROJECT_ID_TOKEN = '{{projectId}}';

const onUncaughtExceptionValues = ['ignore', 'flush', 'flushAndExit'];

const headers: OutgoingHttpHeaders = {};
headers[Constants.TRACE_AGENT_REQUEST_HEADER] = 1;

/* A list of scopes needed to operate with the trace API */
const SCOPES: string[] = ['https://www.googleapis.com/auth/trace.append'];
/* The API endpoint of the Stackdriver Trace service */
const TRACE_API_ENDPOINT = 'cloudtrace.googleapis.com';

export interface TraceWriterConfig {
  authOptions: GoogleAuthOptions;
  onUncaughtException: string;
  bufferSize: number;
  flushDelaySeconds: number;
  stackTraceLimit: number;
  maximumLabelValueSize: number;
  serviceContext: {service?: string; version?: string; minorVersion?: string};
}

export interface LabelObject {
  [key: string]: string;
}

export class TraceBuffer {
  /**
   * Buffered traces.
   */
  private traces: Trace[] = [];
  /**
   * Number of buffered spans; this number must be at least as large as
   * buffer.length.
   */
  private numSpans = 0;

  /**
   * Add a new trace to the buffer.
   * @param trace The trace to add.
   */
  add(trace: Trace) {
    this.traces.push(trace);
    this.numSpans += trace.spans.length;
  }

  /**
   * Gets the number of spans contained within buffered traces.
   */
  getNumSpans() {
    return this.numSpans;
  }

  /**
   * Clears the buffer, returning its original contents.
   */
  drain(): Trace[] {
    const result = this.traces;
    this.traces = [];
    this.numSpans = 0;
    return result;
  }
}

/**
 * A class representing a service that publishes traces in the background.
 */
export class TraceWriter extends Service {
  /** Traces to be published */
  protected buffer: TraceBuffer;
  /** Default labels to be attached to written spans */
  defaultLabels: LabelObject;
  /** Reference to global unhandled exception handler */
  private unhandledException?: () => void;
  /** Whether the trace writer is active */
  isActive: boolean;

  /**
   * Constructs a new TraceWriter instance.
   * @param config A config object containing information about
   *   authorization credentials.
   * @param logger The Trace Agent's logger object.
   * @constructor
   */
  constructor(
    private readonly config: TraceWriterConfig,
    private readonly logger: Logger
  ) {
    super(
      {
        packageJson: pjson,
        projectIdRequired: false,
        apiEndpoint: TRACE_API_ENDPOINT,
        baseUrl: `https://${TRACE_API_ENDPOINT}/v1`,
        scopes: SCOPES,
      },
      config.authOptions
    );

    this.logger = logger;
    this.buffer = new TraceBuffer();
    this.defaultLabels = {};

    this.isActive = true;

    if (onUncaughtExceptionValues.indexOf(config.onUncaughtException) === -1) {
      logger.error(
        `TraceWriter#constructor: The value of config.onUncaughtException [${
          config.onUncaughtException
        }] should be one of [${onUncaughtExceptionValues.join(', ')}].`
      );
      // TODO(kjin): Either log an error or throw one, but not both
      throw new Error('Invalid value for onUncaughtException configuration.');
    }
    const onUncaughtException = config.onUncaughtException;
    if (onUncaughtException !== 'ignore') {
      this.unhandledException = () => {
        this.flushBuffer();
        if (onUncaughtException === 'flushAndExit') {
          setTimeout(() => {
            // eslint-disable-next-line no-process-exit
            process.exit(1);
          }, 2000);
        }
      };
      process.on('uncaughtException', this.unhandledException);
    }
  }

  stop(): void {
    this.isActive = false;
  }

  getConfig(): TraceWriterConfig {
    return this.config;
  }

  async initialize(): Promise<void> {
    // Schedule periodic flushing of the buffer, but only if we are able to get
    // the project number (potentially from the network.)
    const getProjectIdAndScheduleFlush = async () => {
      try {
        await this.getProjectId();
      } catch (err) {
        this.logger.error(
          'TraceWriter#initialize: Unable to acquire the project number',
          'automatically from the GCP metadata service. Please provide a',
          'valid project ID as environmental variable GCLOUD_PROJECT, or',
          `as config.projectId passed to start. Original error: ${err}`
        );
        throw err;
      }
      this.scheduleFlush();
    };
    // getProjectIdAndScheduleFlush has no return value, so no need to capture
    // it on the left-hand side.
    const [hostname, instanceId] = await Promise.all([
      this.getHostname(),
      this.getInstanceId(),
      getProjectIdAndScheduleFlush(),
    ]);
    const addDefaultLabel = (key: string, value: string | number) => {
      this.defaultLabels[key] = `${value}`;
    };
    this.defaultLabels = {};
    addDefaultLabel(
      TraceLabels.AGENT_DATA,
      `node ${pjson.name} v${pjson.version}`
    );
    addDefaultLabel(TraceLabels.GCE_HOSTNAME, hostname!);
    if (instanceId) {
      addDefaultLabel(TraceLabels.GCE_INSTANCE_ID, instanceId);
    }
    const moduleName = this.config.serviceContext.service || hostname;
    addDefaultLabel(TraceLabels.GAE_MODULE_NAME, moduleName!);

    const moduleVersion = this.config.serviceContext.version;
    if (moduleVersion) {
      addDefaultLabel(TraceLabels.GAE_MODULE_VERSION, moduleVersion);
      const minorVersion = this.config.serviceContext.minorVersion;
      if (minorVersion) {
        let versionLabel = '';
        if (moduleName !== 'default') {
          versionLabel = moduleName + ':';
        }
        versionLabel += moduleVersion + '.' + minorVersion;
        addDefaultLabel(TraceLabels.GAE_VERSION, versionLabel);
      }
    }
    Object.freeze(this.defaultLabels);
  }

  private async getHostname(): Promise<string> {
    try {
      return await gcpMetadata.instance({property: 'hostname', headers});
    } catch (err) {
      if (err.code !== 'ENOTFOUND') {
        // We are running on GCP.
        this.logger.warn(
          'TraceWriter#getHostname: Encountered an error while',
          'retrieving GCE hostname from the GCP metadata service',
          `(metadata.google.internal): ${err}`
        );
      }
      return os.hostname();
    }
  }

  private async getInstanceId(): Promise<number | null> {
    try {
      return await gcpMetadata.instance({property: 'id', headers});
    } catch (err) {
      if (err.code !== 'ENOTFOUND') {
        // We are running on GCP.
        this.logger.warn(
          'TraceWriter#getInstanceId: Encountered an error while',
          'retrieving GCE instance ID from the GCP metadata service',
          `(metadata.google.internal): ${err}`
        );
      }
      return null;
    }
  }

  getProjectId() {
    // super.getProjectId writes to projectId, but doesn't check it first
    // before going through the flow of obtaining it. So we add that logic
    // first.
    if (this.projectId !== NO_PROJECT_ID_TOKEN) {
      return Promise.resolve(this.projectId);
    }
    return super.getProjectId();
  }

  /**
   * Queues a trace to be published. Spans with no end time are excluded.
   *
   * @param trace The trace to be queued.
   */
  writeTrace(trace: Trace) {
    const publishableSpans = trace.spans.filter(span => !!span.endTime);

    publishableSpans.forEach(spanData => {
      if (spanData.kind === SpanKind.RPC_SERVER) {
        // Copy properties from the default labels.
        Object.assign(spanData.labels, this.defaultLabels);
      }
    });

    this.buffer.add({
      traceId: trace.traceId,
      projectId: trace.projectId,
      spans: publishableSpans,
    });
    this.logger.info(
      `TraceWriter#writeTrace: number of buffered spans = ${this.buffer.getNumSpans()}`
    );
    // Publish soon if the buffer is getting big
    if (this.buffer.getNumSpans() >= this.config.bufferSize) {
      this.logger.info('TraceWriter#writeTrace: Trace buffer full, flushing.');
      setImmediate(() => this.flushBuffer());
    }
  }

  /**
   * Flushes the buffer of traces at a regular interval controlled by the
   * flushDelay property of this TraceWriter's config.
   */
  private scheduleFlush() {
    this.logger.info('TraceWriter#scheduleFlush: Performing periodic flush.');
    this.flushBuffer();

    // Do it again after delay
    if (this.isActive) {
      // 'global.setTimeout' avoids TS2339 on this line.
      // It helps disambiguate the Node runtime setTimeout function from
      // WindowOrWorkerGlobalScope.setTimeout, which returns an integer.
      global
        .setTimeout(
          this.scheduleFlush.bind(this),
          this.config.flushDelaySeconds * 1000
        )
        .unref();
    }
  }

  /**
   * Serializes the buffered traces to be published asynchronously.
   */
  private flushBuffer() {
    // Privatize and clear the buffer.
    const flushedTraces = this.buffer.drain();
    if (flushedTraces.length === 0) {
      return;
    }

    const afterProjectId = (projectId: string) => {
      flushedTraces.forEach(trace => (trace.projectId = projectId));
      this.logger.debug(
        'TraceWriter#flushBuffer: Flushing traces',
        flushedTraces
      );
      this.publish(JSON.stringify({traces: flushedTraces}));
    };

    // TODO(kjin): We should always be following the 'else' path.
    // Any test that doesn't mock the Trace Writer will assume that traces get
    // buffered synchronously. We need to refactor those tests to remove that
    // assumption before we can make this fix.
    if (this.projectId !== NO_PROJECT_ID_TOKEN) {
      afterProjectId(this.projectId);
    } else {
      this.getProjectId().then(afterProjectId, () => {
        // Because failing to get a project ID means that the trace agent will
        // get disabled, there is a very small window for this code path to be
        // taken. For this reason we don't do anything more complex than just
        // notifying that we are dropping the current traces.
        this.logger.info(
          'TraceWriter#flushBuffer: No project ID, dropping traces.'
        );
      });
    }
  }

  /**
   * Publishes flushed traces to the network.
   * @param json The stringified json representation of the queued traces.
   */
  protected publish(json: string) {
    const hostname = 'cloudtrace.googleapis.com';
    const uri = `https://${hostname}/v1/projects/${this.projectId}/traces`;
    const options: DecorateRequestOptions = {
      method: 'PATCH',
      uri,
      body: json,
      headers,
    };
    this.logger.info('TraceWriter#publish: Publishing to ' + uri);
    this.request(options, (err, body?, response?) => {
      const statusCode = response && response.statusCode;
      if (err) {
        this.logger.error(
          `TraceWriter#publish: Received error ${
            statusCode ? `with status code ${statusCode}` : ''
          } while publishing traces to ${hostname}: ${err}`
        );
      } else {
        this.logger.info(
          `TraceWriter#publish: Published w/ status code: ${statusCode}`
        );
      }
    });
  }
}

export const traceWriter = new Singleton(TraceWriter);