// Copyright 2015 Google LLC
//
// 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 crypto from 'crypto';
import * as util from 'util';

import {Constants, SpanType} from './constants';
import {RootSpan, Span, SpanOptions, TraceContext} from './plugin-types';
import {SpanKind, Trace, TraceSpan} from './trace';
import {TraceLabels} from './trace-labels';
import {traceWriter} from './trace-writer';
import * as traceUtil from './util';

// Use 6 bytes of randomness only as JS numbers are doubles not 64-bit ints.
const SPAN_ID_RANDOM_BYTES = 6;

// Use the faster crypto.randomFillSync when available (Node 7+) falling back to
// using crypto.randomBytes.
const spanIdBuffer = Buffer.alloc(SPAN_ID_RANDOM_BYTES);
const randomFillSync = crypto.randomFillSync;
const randomBytes = crypto.randomBytes;
const spanRandomBuffer = randomFillSync
  ? () => randomFillSync(spanIdBuffer)
  : () => randomBytes(SPAN_ID_RANDOM_BYTES);

function randomSpanId() {
  return parseInt(spanRandomBuffer().toString('hex'), 16).toString();
}

/**
 * Represents a real trace span.
 */
export abstract class BaseSpanData implements Span {
  readonly span: TraceSpan;
  abstract readonly type: SpanType;

  /**
   * Creates a trace context object.
   * @param trace The object holding the spans comprising this trace.
   * @param spanName The name of the span.
   * @param parentSpanId The ID of the parent span, or '0' to specify that there
   *                     is none.
   * @param skipFrames the number of frames to remove from the top of the stack
   *                   when collecting the stack trace.
   */
  constructor(
    readonly trace: Trace,
    spanName: string,
    parentSpanId: string,
    skipFrames: number
  ) {
    this.span = {
      name: traceUtil.truncate(
        spanName,
        Constants.TRACE_SERVICE_SPAN_NAME_LIMIT
      ),
      startTime: new Date().toISOString(),
      endTime: '',
      spanId: randomSpanId(),
      kind: SpanKind.SPAN_KIND_UNSPECIFIED,
      parentSpanId,
      labels: {},
    };
    this.trace.spans.push(this.span);

    const stackFrames = traceUtil.createStackTrace(
      traceWriter.get().getConfig().stackTraceLimit,
      skipFrames,
      this.constructor
    );
    if (stackFrames.length > 0) {
      // Developer note: This is not equivalent to using addLabel, because the
      // stack trace label has its own size constraints.
      this.span.labels[TraceLabels.STACK_TRACE_DETAILS_KEY] =
        traceUtil.truncate(
          JSON.stringify({stack_frame: stackFrames}),
          Constants.TRACE_SERVICE_LABEL_VALUE_LIMIT
        );
    }
  }

  getTraceContext() {
    return {
      traceId: this.trace.traceId.toString(),
      spanId: this.span.spanId.toString(),
      options: 1, // always traced
    };
  }

  // eslint-disable-next-line @typescript-eslint/no-explicit-any
  addLabel(key: string, value: any) {
    const k = traceUtil.truncate(key, Constants.TRACE_SERVICE_LABEL_KEY_LIMIT);
    const stringValue = typeof value === 'string' ? value : util.inspect(value);
    const v = traceUtil.truncate(
      stringValue,
      traceWriter.get().getConfig().maximumLabelValueSize
    );
    this.span.labels[k] = v;
  }

  endSpan(timestamp?: Date) {
    if (this.span.endTime) {
      return;
    }
    timestamp = timestamp || new Date();
    this.span.endTime = timestamp.toISOString();
  }
}

/**
 * Represents a real root span, which corresponds to an incoming request.
 */
export class RootSpanData extends BaseSpanData implements RootSpan {
  readonly type = SpanType.ROOT;
  // Locally-tracked list of children. Used only to determine, once this span
  // ends, whether a child still needs to be published.
  private children: ChildSpanData[] = [];

  constructor(
    trace: Trace,
    spanName: string,
    parentSpanId: string,
    skipFrames: number
  ) {
    super(trace, spanName, parentSpanId, skipFrames);
    this.span.kind = SpanKind.RPC_SERVER;
  }

  createChildSpan(options?: SpanOptions): Span {
    options = options || {name: ''};
    const skipFrames = options.skipFrames ? options.skipFrames + 1 : 1;
    const child = new ChildSpanData(
      this.trace /* Trace object */,
      options.name /* Span name */,
      this.span.spanId /* Parent's span ID */,
      skipFrames
    ); /* # of frames to skip in stack trace */
    this.children.push(child);
    return child;
  }

  endSpan(timestamp?: Date) {
    if (this.span.endTime) {
      return;
    }
    super.endSpan(timestamp);
    traceWriter.get().writeTrace(this.trace);
    this.children.forEach(child => {
      if (!child.span.endTime) {
        // Child hasn't ended yet.
        // Inform the child that it needs to self-publish.
        child.shouldSelfPublish = true;
      }
    });
    // We no longer need to keep track of our children.
    this.children = [];
  }
}

/**
 * Represents a real child span, which corresponds to an outgoing RPC.
 */
export class ChildSpanData extends BaseSpanData {
  readonly type = SpanType.CHILD;
  // Whether this span should publish itself. This is meant to be set to true
  // by the parent RootSpanData.
  shouldSelfPublish = false;

  constructor(
    trace: Trace,
    spanName: string,
    parentSpanId: string,
    skipFrames: number
  ) {
    super(trace, spanName, parentSpanId, skipFrames);
    this.span.kind = SpanKind.RPC_CLIENT;
  }

  endSpan(timestamp?: Date) {
    if (this.span.endTime) {
      return;
    }
    super.endSpan(timestamp);
    if (this.shouldSelfPublish) {
      // Also, publish just this span.
      traceWriter.get().writeTrace({
        projectId: this.trace.projectId,
        traceId: this.trace.traceId,
        spans: [this.span],
      });
    }
  }
}

// Helper function to generate static virtual trace spans.
function createPhantomSpanData<T extends SpanType>(
  spanType: T
): Span & {readonly type: T} {
  return Object.freeze(
    Object.assign(
      {
        getTraceContext() {
          return null;
        },
        // eslint-disable-next-line
        addLabel(key: string, value: any) {},
        endSpan() {},
      },
      {type: spanType}
    )
  );
}

/**
 * Helper (and base) class for UntracedRootSpanData. Represents an untraced
 * child span.
 */
class UntracedSpanData implements Span {
  readonly type = SpanType.UNSAMPLED;
  protected readonly traceContext: TraceContext;

  constructor(traceId: string) {
    this.traceContext = {
      traceId,
      spanId: randomSpanId(),
      options: 0, // Not traced.
    };
  }

  getTraceContext(): traceUtil.TraceContext | null {
    return this.traceContext;
  }

  // No-op.
  addLabel(): void {}
  // No-op.
  endSpan(): void {}
}

/**
 * Represents an "untraced" root span (aka not published).
 * For distributed trace context propagation purposes.
 */
export class UntracedRootSpanData extends UntracedSpanData implements RootSpan {
  private child: Span | null = null;

  createChildSpan(): Span {
    if (!this.child) {
      this.child = new UntracedSpanData(this.traceContext.traceId);
    }
    return this.child;
  }
}

/**
 * A virtual trace span that indicates that a real child span couldn't be
 * created because the correct root span couldn't be determined.
 */
export const UNCORRELATED_CHILD_SPAN = createPhantomSpanData(
  SpanType.UNCORRELATED
);

/**
 * A virtual trace span that indicates that a real child span couldn't be
 * created because the Trace Agent was disabled.
 */
export const DISABLED_CHILD_SPAN = createPhantomSpanData(SpanType.DISABLED);

/**
 * A virtual trace span that indicates that a real root span couldn't be
 * created because an active root span context already exists.
 */
export const UNCORRELATED_ROOT_SPAN = Object.freeze(
  Object.assign(
    {
      createChildSpan() {
        return UNCORRELATED_CHILD_SPAN;
      },
    },
    UNCORRELATED_CHILD_SPAN
  )
);

/**
 * A virtual trace span that indicates that a real root span couldn't be
 * created because it was disallowed by user configuration.
 */
export const DISABLED_ROOT_SPAN = Object.freeze(
  Object.assign(
    {
      createChildSpan() {
        return DISABLED_CHILD_SPAN;
      },
    },
    DISABLED_CHILD_SPAN
  )
);