# CLAUDE.md

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

## Project Overview

KML Track Editor is a single-page web application for viewing, editing, and navigating KML/GPS tracks on an interactive map. The entire application is contained in `index.html`.

## Development

To run locally, serve via HTTP (required for GPS geolocation API):
```bash
python -m http.server 8000
```
Then open http://localhost:8000

## Architecture

### Single-File Application
Everything is in `index.html`:
- **Lines 1-325**: CSS styles
- **Lines 326-420**: HTML structure (map, controls sidebar, overlays)
- **Lines 421-end**: JavaScript application code

### Key Libraries (loaded from CDN)
- **Leaflet.js 1.9.4**: Map rendering and interaction
- **leaflet-rotate 0.2.8**: Map rotation for navigation mode

### Core State Variables (around line 457-514)
- `tracks[]`: All loaded track objects with `{id, name, coords, layer, color}`
- `selectedTracks[]`: Currently selected tracks for multi-selection operations
- `currentTool`: Active editing tool ('select', 'draw', 'reshape', 'smooth', 'delete')
- `navMode`: Whether in navigation mode vs edit mode
- `currentRoute`: Pathfinding result for navigation

### Major Feature Areas

**Track Editing**:
- Draw new tracks, reshape existing ones with rope physics, smooth brush tool
- Track snapping at endpoints (auto-splits target track at snap point)
- Multi-track selection and merge operations
- Undo system with 20-step history

**Navigation Mode**:
- Graph-based pathfinding using Dijkstra's algorithm across connected trails
- Trail intersections detected within 5 meters (`INTERSECTION_THRESHOLD`)
- Real-time route recalculation when user deviates >50m from path
- Map rotation to face direction of travel (uses `map.setBearing()`)
- Auto-center on GPS position (toggleable)
- Destination persistence in localStorage

**GPS Integration**:
- Uses `navigator.geolocation.watchPosition` with backup polling every 3 seconds
- Requires HTTPS or localhost to function

### File Loading
- Automatically loads `default.kml` on startup if present
- KML parsing via DOMParser extracting `<Placemark>` coordinates