packages/core/src/context/tracer.ts

/**
 * @license
 * Copyright 2026 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import { debugLogger } from '../utils/debugLogger.js';
import * as fsSync from 'node:fs';
import * as path from 'node:path';
import { randomUUID } from 'node:crypto';

export interface ContextTracerOptions {
  enabled?: boolean;
  targetDir: string;
  sessionId: string;
}

export class ContextTracer {
  private traceDir: string;
  private assetsDir: string;
  private enabled: boolean;

  private readonly MAX_INLINE_SIZE = 1000;

  constructor(options: ContextTracerOptions) {
    this.enabled = options.enabled ?? false;

    this.traceDir =
      process.env['GEMINI_CONTEXT_TRACE_DIR'] ||
      path.join(options.targetDir, 'context_trace', options.sessionId);
    this.assetsDir = path.join(this.traceDir, 'assets');

    if (this.enabled) {
      try {
        fsSync.mkdirSync(this.assetsDir, { recursive: true });
        this.logEvent('SYSTEM', 'Context Tracer Initialized', {
          sessionId: options.sessionId,
        });
      } catch (e) {
        debugLogger.error('Failed to initialize ContextTracer', e);
        this.enabled = false;
      }
    }
  }

  logEvent(
    component: string,
    action: string,
    details?: Record<string, unknown>,
  ) {
    if (!this.enabled) return;
    try {
      let processedDetails: Record<string, unknown> | undefined;

      if (details) {
        processedDetails = {};
        for (const [key, value] of Object.entries(details)) {
          const strValue =
            typeof value === 'string' ? value : JSON.stringify(value);
          if (strValue && strValue.length > this.MAX_INLINE_SIZE) {
            const assetId = this.saveAsset(component, key, value);
            processedDetails[key] = { $asset: assetId };
          } else {
            processedDetails[key] = value;
          }
        }
      }

      const timestamp = new Date().toISOString();
      const detailsStr = processedDetails
        ? ` | Details: ${JSON.stringify(processedDetails)}`
        : '';
      const logLine = `[${timestamp}] [${component}] ${action}${detailsStr}\n`;
      fsSync.appendFileSync(
        path.join(this.traceDir, 'trace.log'),
        logLine,
        'utf-8',
      );
    } catch (e) {
      debugLogger.warn(`Tracing failed: ${e}`);
    }
  }

  private saveAsset(
    component: string,
    assetName: string,
    data: unknown,
  ): string {
    if (!this.enabled) return 'asset-recording-disabled';
    try {
      const assetId = `${Date.now()}-${randomUUID()}-${assetName}.json`;
      const assetPath = path.join(this.assetsDir, assetId);

      fsSync.writeFileSync(assetPath, JSON.stringify(data, null, 2), 'utf-8');
      this.logEvent(component, `Saved asset: ${assetName}`, { assetId });
      return assetId;
    } catch (e) {
      this.logEvent(component, `Failed to save asset: ${assetName}`, {
        error: String(e),
      });
      return 'asset-save-failed';
    }
  }
}