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* Exercise 14: Build a Metrics Tracker with Metadata
*
* Goal: Learn to use config metadata and track metrics
*
* In this exercise, you'll:
* 1. Build a stateful callback that tracks metrics
* 2. Use config.metadata to track user information
* 3. Measure execution time for each Runnable
* 4. Generate a summary report
*
* This teaches you how to pass context through your chains!
*/
import {Runnable} from '../../../../src/index.js';
import {BaseCallback} from '../../../../src/utils/callbacks.js';
class MetricsTrackerCallback extends BaseCallback {
constructor() {
super();
// Track when each call started
this.startTimes = new Map();
// Metrics per runnable
this.metrics = {};
}
async onStart(runnable, input, config) {
const key = `${runnable.constructor.name}_${Date.now()}_${Math.random()}`;
this.startTimes.set(key, Date.now());
const userId = config?.metadata?.userId;
const runnableName = runnable.constructor.name;
if (!this.metrics[runnableName]) {
this.metrics[runnableName] = {
totalCalls: 0,
totalTime: 0,
users: new Set()
};
}
this.metrics[runnableName].totalCalls++;
if (userId) {
this.metrics[runnableName].users.add(userId);
}
// Store key for matching in onEnd
config._metricsKey = key;
}
async onEnd(runnable, output, config) {
const key = config._metricsKey;
const startTime = this.startTimes.get(key);
if (startTime) {
const duration = Date.now() - startTime;
const runnableName = runnable.constructor.name;
if (this.metrics[runnableName]) {
this.metrics[runnableName].totalTime += duration;
}
this.startTimes.delete(key);
}
}
async onError(runnable, error, config) {
const key = config._metricsKey;
if (key) {
this.startTimes.delete(key);
}
}
getReport() {
const report = {};
for (const [name, data] of Object.entries(this.metrics)) {
report[name] = {
calls: data.totalCalls,
totalTime: data.totalTime,
avgTime: data.totalCalls > 0 ? Math.round(data.totalTime / data.totalCalls) : 0,
users: Array.from(data.users)
};
}
return report;
}
printReport() {
console.log('\n📊 Metrics Report:');
console.log('─'.repeat(60));
const report = this.getReport();
for (const [name, data] of Object.entries(report)) {
console.log(`${name}:`);
console.log(` Calls: ${data.calls}`);
console.log(` Total Time: ${data.totalTime}ms`);
console.log(` Avg Time: ${data.avgTime}ms`);
console.log(` Users: ${data.users.join(', ')}`);
console.log('');
}
}
}
// Test Runnables with different speeds
class FastRunnable extends Runnable {
async _call(input, config) {
await new Promise(resolve => setTimeout(resolve, 100));
return `Fast: ${input}`;
}
}
class SlowRunnable extends Runnable {
async _call(input, config) {
await new Promise(resolve => setTimeout(resolve, 500));
return `Slow: ${input}`;
}
}
class MediumRunnable extends Runnable {
async _call(input, config) {
await new Promise(resolve => setTimeout(resolve, 250));
return `Medium: ${input}`;
}
}
async function exercise() {
console.log('=== Exercise 14: Metrics Tracker with Metadata ===\n');
const metrics = new MetricsTrackerCallback();
const fast = new FastRunnable();
const medium = new MediumRunnable();
const slow = new SlowRunnable();
// Test 1: User 1 makes some calls
console.log('--- User 1 making calls ---');
await fast.invoke('test1', { callbacks: [metrics], metadata: { userId: "user_123" } });
await medium.invoke('test2', { callbacks: [metrics], metadata: { userId: "user_123" } });
await fast.invoke('test3', { callbacks: [metrics], metadata: { userId: "user_123" } });
// Test 2: User 2 makes different calls
console.log('--- User 2 making calls ---');
await slow.invoke('test4', { callbacks: [metrics], metadata: { userId: "user_456" } });
await fast.invoke('test5', { callbacks: [metrics], metadata: { userId: "user_456" } });
// Test 3: User 3 makes calls
console.log('--- User 3 making calls ---');
await medium.invoke('test6', { callbacks: [metrics], metadata: { userId: "user_789" } });
await slow.invoke('test7', { callbacks: [metrics], metadata: { userId: "user_789" } });
await medium.invoke('test8', { callbacks: [metrics], metadata: { userId: "user_789" } });
metrics.printReport();
console.log('\n✓ Exercise 2 complete!');
}
// Run the exercise
exercise().catch(console.error);
/**
* Expected Output:
*
* 📊 Metrics Report:
* ────────────────────────────────────────────────────────────
* FastRunnable:
* Calls: 3
* Total Time: 305ms
* Avg Time: 102ms
* Users: user_123, user_456
*
* SlowRunnable:
* Calls: 2
* Total Time: 1008ms
* Avg Time: 504ms
* Users: user_456, user_789
*
* MediumRunnable:
* Calls: 3
* Total Time: 756ms
* Avg Time: 252ms
* Users: user_123, user_789
*
* Learning Points:
* 1. Stateful callbacks can accumulate data
* 2. config.metadata passes arbitrary context
* 3. Useful for tracking per-user metrics
* 4. Map.set() and Map.get() for tracking start times
* 5. Report generation for observability
*/ |