# Step 2 — LDF Loading & Display

## What Was Built

LDF file parsing, GUI table population, baud rate detection, schedule table loading, and auto-reload on file change.

## Architecture

```
User clicks Browse → QFileDialog → file_path
                                       │
                                       ▼
                              _load_ldf_file(path)
                                       │
                          ┌────────────┼────────────┐
                          ▼            ▼            ▼
                    parse_ldf()   On error:    Setup file
                    (ldf_handler)  show dialog   watcher
                          │
                          ▼
                       LdfData
                     ┌────┼────────────┬──────────────┐
                     ▼    ▼            ▼              ▼
                  Baud  Tx table    Rx table      Schedule
                  rate  (master    (slave         dropdown
                  label  frames)    frames)
```

## Key Module: ldf_handler.py

Adapter between `ldfparser` library and our GUI. Converts complex library objects into simple dataclasses:

| Dataclass | Purpose |
|-----------|---------|
| `LdfData` | Complete parsed result — baudrate, frames, schedules |
| `FrameInfo` | One frame: name, ID, publisher, length, is_master_tx, signals |
| `SignalInfo` | One signal: name, bit_offset, width, init_value |
| `ScheduleTableInfo` | One schedule: name, entries [(frame_name, delay_ms)] |

### ldfparser API notes
- `ldf.baudrate` returns bps * 1000 (19200 kbps → 19200000) — divide by 1000
- `frame.signal_map` is list of (bit_offset, LinSignal) tuples
- `frame.publisher` is LinMaster or LinSlave — use isinstance() to classify
- Schedule delay is in seconds (0.01 = 10ms) — multiply by 1000

## Features

- **LDF parsing**: Extracts frames, signals, schedules, baud rate
- **Tx table**: Populated with master frames (name, ID, length, interval, data, signals)
- **Rx table**: Prepared with slave frame definitions (data filled at runtime)
- **Baud rate**: Auto-detected from LDF's LIN_speed field
- **Schedule dropdown**: Populated with schedule table names
- **Per-frame intervals**: Auto-filled from first schedule table
- **Auto-reload**: QFileSystemWatcher detects file changes, re-parses automatically
- **Error handling**: Invalid files show error dialog, don't corrupt GUI state

## Files

| File | Purpose |
|------|---------|
| `python/src/ldf_handler.py` | LDF parsing adapter — parse_ldf() → LdfData |
| `python/src/main_window.py` | Updated with _load_ldf_file(), table population, file watcher |
| `python/tests/test_ldf_handler.py` | 27 tests for the parsing layer |
| `python/tests/test_ldf_loading.py` | 20 tests for GUI integration |
| `resources/sample.ldf` | Sample LIN 2.1 LDF with 4 frames, 2 schedule tables |

## Test Results
- 79 total tests passing (Step 1: 32 + Step 2: 47)
- Parser tests: valid/invalid files, frame classification, signal extraction, schedules
- GUI tests: table population, baud rate, schedule combo, error handling, auto-reload