JavaScript Analytics Tracking Script

I need a JavaScript tracking script (analytics.js) to collect anonymous user behavior data on e-commerce platforms. The script should be lightweight (under 20kb) and can be auto-sent via a POST request to the /track endpoint.

Essential Features:

1. Page View Tracking
- Capture Page URL, Referrer, Timestamp

2. Scroll Depth Tracking
- Maximum scroll percentage, once per session

3. Button Click Tracking
- Tag elements with data-track attribute, capture text/ID of clicked button

4. Video Watch Progress
- Track HTML5 and YouTube video watch time

5. Session Metadata
- Screen dimensions, device type, browser/platform, time on page

6. Additional User Actions
- Form submissions, mouse movements, custom events

Ideal Skills and Experience:
- Strong in JavaScript
- Experience with data tracking and analytics
- Familiarity with e-commerce platforms
- Knowledge of handling video tracking in various players

Looking for someone who can deliver a reliable and efficient tracking solution.