1 files changed, 207 insertions, 0 deletions
diff --git a/packages/core/src/telemetry/uiTelemetry.ts b/packages/core/src/telemetry/uiTelemetry.ts
new file mode 100644
index 00000000..71409696
--- /dev/null
+++ b/packages/core/src/telemetry/uiTelemetry.ts
@@ -0,0 +1,207 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { EventEmitter } from 'events';
+import {
+  EVENT_API_ERROR,
+  EVENT_API_RESPONSE,
+  EVENT_TOOL_CALL,
+} from './constants.js';
+
+import {
+  ApiErrorEvent,
+  ApiResponseEvent,
+  ToolCallEvent,
+  ToolCallDecision,
+} from './types.js';
+
+export type UiEvent =
+  | (ApiResponseEvent & { 'event.name': typeof EVENT_API_RESPONSE })
+  | (ApiErrorEvent & { 'event.name': typeof EVENT_API_ERROR })
+  | (ToolCallEvent & { 'event.name': typeof EVENT_TOOL_CALL });
+
+export interface ToolCallStats {
+  count: number;
+  success: number;
+  fail: number;
+  durationMs: number;
+  decisions: {
+    [ToolCallDecision.ACCEPT]: number;
+    [ToolCallDecision.REJECT]: number;
+    [ToolCallDecision.MODIFY]: number;
+  };
+}
+
+export interface ModelMetrics {
+  api: {
+    totalRequests: number;
+    totalErrors: number;
+    totalLatencyMs: number;
+  };
+  tokens: {
+    prompt: number;
+    candidates: number;
+    total: number;
+    cached: number;
+    thoughts: number;
+    tool: number;
+  };
+}
+
+export interface SessionMetrics {
+  models: Record<string, ModelMetrics>;
+  tools: {
+    totalCalls: number;
+    totalSuccess: number;
+    totalFail: number;
+    totalDurationMs: number;
+    totalDecisions: {
+      [ToolCallDecision.ACCEPT]: number;
+      [ToolCallDecision.REJECT]: number;
+      [ToolCallDecision.MODIFY]: number;
+    };
+    byName: Record<string, ToolCallStats>;
+  };
+}
+
+const createInitialModelMetrics = (): ModelMetrics => ({
+  api: {
+    totalRequests: 0,
+    totalErrors: 0,
+    totalLatencyMs: 0,
+  },
+  tokens: {
+    prompt: 0,
+    candidates: 0,
+    total: 0,
+    cached: 0,
+    thoughts: 0,
+    tool: 0,
+  },
+});
+
+const createInitialMetrics = (): SessionMetrics => ({
+  models: {},
+  tools: {
+    totalCalls: 0,
+    totalSuccess: 0,
+    totalFail: 0,
+    totalDurationMs: 0,
+    totalDecisions: {
+      [ToolCallDecision.ACCEPT]: 0,
+      [ToolCallDecision.REJECT]: 0,
+      [ToolCallDecision.MODIFY]: 0,
+    },
+    byName: {},
+  },
+});
+
+export class UiTelemetryService extends EventEmitter {
+  #metrics: SessionMetrics = createInitialMetrics();
+  #lastPromptTokenCount = 0;
+
+  addEvent(event: UiEvent) {
+    switch (event['event.name']) {
+      case EVENT_API_RESPONSE:
+        this.processApiResponse(event);
+        break;
+      case EVENT_API_ERROR:
+        this.processApiError(event);
+        break;
+      case EVENT_TOOL_CALL:
+        this.processToolCall(event);
+        break;
+      default:
+        // We should not emit update for any other event metric.
+        return;
+    }
+
+    this.emit('update', {
+      metrics: this.#metrics,
+      lastPromptTokenCount: this.#lastPromptTokenCount,
+    });
+  }
+
+  getMetrics(): SessionMetrics {
+    return this.#metrics;
+  }
+
+  getLastPromptTokenCount(): number {
+    return this.#lastPromptTokenCount;
+  }
+
+  private getOrCreateModelMetrics(modelName: string): ModelMetrics {
+    if (!this.#metrics.models[modelName]) {
+      this.#metrics.models[modelName] = createInitialModelMetrics();
+    }
+    return this.#metrics.models[modelName];
+  }
+
+  private processApiResponse(event: ApiResponseEvent) {
+    const modelMetrics = this.getOrCreateModelMetrics(event.model);
+
+    modelMetrics.api.totalRequests++;
+    modelMetrics.api.totalLatencyMs += event.duration_ms;
+
+    modelMetrics.tokens.prompt += event.input_token_count;
+    modelMetrics.tokens.candidates += event.output_token_count;
+    modelMetrics.tokens.total += event.total_token_count;
+    modelMetrics.tokens.cached += event.cached_content_token_count;
+    modelMetrics.tokens.thoughts += event.thoughts_token_count;
+    modelMetrics.tokens.tool += event.tool_token_count;
+
+    this.#lastPromptTokenCount = event.input_token_count;
+  }
+
+  private processApiError(event: ApiErrorEvent) {
+    const modelMetrics = this.getOrCreateModelMetrics(event.model);
+    modelMetrics.api.totalRequests++;
+    modelMetrics.api.totalErrors++;
+    modelMetrics.api.totalLatencyMs += event.duration_ms;
+  }
+
+  private processToolCall(event: ToolCallEvent) {
+    const { tools } = this.#metrics;
+    tools.totalCalls++;
+    tools.totalDurationMs += event.duration_ms;
+
+    if (event.success) {
+      tools.totalSuccess++;
+    } else {
+      tools.totalFail++;
+    }
+
+    if (!tools.byName[event.function_name]) {
+      tools.byName[event.function_name] = {
+        count: 0,
+        success: 0,
+        fail: 0,
+        durationMs: 0,
+        decisions: {
+          [ToolCallDecision.ACCEPT]: 0,
+          [ToolCallDecision.REJECT]: 0,
+          [ToolCallDecision.MODIFY]: 0,
+        },
+      };
+    }
+
+    const toolStats = tools.byName[event.function_name];
+    toolStats.count++;
+    toolStats.durationMs += event.duration_ms;
+    if (event.success) {
+      toolStats.success++;
+    } else {
+      toolStats.fail++;
+    }
+
+    if (event.decision) {
+      tools.totalDecisions[event.decision]++;
+      toolStats.decisions[event.decision]++;
+    }
+  }
+}
+
+export const uiTelemetryService = new UiTelemetryService();