CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Project Overview

Gym Tracker is a containerized web application for tracking gym sessions and muscle group training frequency. It displays a heatmap of workout sessions, tracks muscle group balance, and provides insights into training patterns.

Tech Stack:

Backend: Node.js with Express (REST API)
Database: SQLite (file-based, for simplicity)
Frontend: Vanilla JavaScript (no build process)
Deployment: Docker container with Nginx reverse proxy

Commands

Backend Development

# Install dependencies
cd backend && npm install

# Start the backend server (port 3000)
npm start

Docker

# Build the Docker image
docker build -t gym-tracker .

# Run the container
docker run -p 80:80 -p 3000:3000 -v $(pwd)/data:/app/data gym-tracker

# Note: Volume mount for /app/data ensures SQLite database persists across restarts

Architecture

Backend Structure

backend/server.js: Express server with REST API endpoints
- GET /api/sessions - Fetch all gym sessions
- POST /api/sessions - Create new session (requires date and muscle_groups array)
- PUT /api/sessions/:id - Update existing session
- DELETE /api/sessions/:id - Delete session
backend/database.js: SQLite database layer with schema and query functions
Database schema: Single sessions table with columns: id (TEXT), date (TEXT, ISO format), muscle_groups (TEXT, JSON array)

Frontend Structure

frontend/index.html: Main HTML structure
frontend/app.js: Core application logic and state management
frontend/api.js: API client for backend communication
frontend/styles.css: Application styling
Frontend architecture: Modular vanilla JS without build tools, served directly by Nginx

Muscle Groups

The application tracks 6 muscle groups: Chest, Legs, Delts (shoulders), Lats (back), Triceps, Biceps

Balance Indicator Logic

Happy: All 6 muscle groups trained 2+ times in last 7 days
Neutral: All 6 muscle groups trained 1+ times in last 7 days
Angry: Any muscle group not trained in last 7 days

Docker Configuration

Single container runs both Nginx (frontend) and Express (backend)
Nginx serves static files and proxies /api/* requests to Express
SQLite database requires volume mount for persistence
Ports: 80 (Nginx/HTTP), 3000 (Express API)

Important Implementation Details

Date Format

All dates are stored and transmitted in ISO 8601 format (YYYY-MM-DD) for consistency between frontend and backend.

Session IDs

Sessions use UUID format for unique identification.

Muscle Groups Storage

Muscle groups are stored as JSON-encoded arrays in the SQLite TEXT column, e.g., ["Chest", "Legs", "Delts"].

Heatmap Implementation

Uses Cal-Heatmap library (loaded via CDN) to visualize workout frequency across the year.

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