# Breakpoint Implementation Status

## What I've Implemented

### Core Architecture ✅
- **`Interpreter.step_once()`** - Executes one line and returns status
  - Returns: `{'status': 'breakpoint'|'running'|'completed'|'error', 'line': N}`
  - Tested and working (see `test_breakpoint_final.py`)

### UI Integration ✅ (Code Complete)
- **`_start_execution()`** - Initializes interpreter
- **`_execution_timer()`** - Runs program in slices of 100 lines
- **Breakpoint pause** - Returns to npyscreen event loop when breakpoint hit
- **Key handlers** - C/S/E keys handled only when `paused_at_breakpoint == True`

### Features
- ✅ Set/remove breakpoints with 'b' key (● marker)
- ✅ Detect breakpoints during execution
- ✅ Pause at breakpoint and show status bar
- ✅ Continue (C) - removes breakpoint and resumes
- ✅ Step (S) - executes one line
- ✅ End (E) - stops execution
- ✅ Keys only work as debug commands when paused

## Testing Status

### What I've Tested
- ✅ **Interpreter step execution** - Fully tested with `test_breakpoint_final.py`
  - Breakpoints detect correctly
  - Status returned correctly
  - Can continue execution after breakpoint

### What I Cannot Test
- ❌ **Full curses UI** - Requires real interactive terminal
  - Automated curses testing needs PTY, pexpect, or expect
  - My attempts with pyte failed (ioctl errors)
  - Would need real user in real terminal

## Code Quality

### Architecture
The implementation follows the correct pattern:
1. UI calls `interpreter.step_once()` repeatedly
2. When status == 'breakpoint', UI sets `paused_at_breakpoint = True`
3. UI returns to npyscreen event loop
4. User presses C/S/E
5. Form handler checks `paused_at_breakpoint` before handling
6. Handler calls backend method to continue/step/end

This is the RIGHT way - no blocking, no callbacks during execution, UI stays in control.

### Key Code Locations

**Interpreter** (`src/interpreter.py`):
- Line 92-173: `step_once()` method

**UI Backend** (`src/ui/curses_ui.py`):
- Line 530-598: `_start_execution()` - Initialize
- Line 600-658: `_execution_timer()` - Run program in slices
- Line 680-714: `_wait_for_breakpoint_input()` - Handle keys at breakpoint
- Line 716-755: `_handle_breakpoint_*()` - Continue/Step/End handlers

**Form Handlers** (`src/ui/curses_ui.py`):
- Line 66-81: Key bindings for C/S/E
- Line 99-113: `h_breakpoint_key()` - Only handles if paused

## Known Limitations

1. **Not tested in real terminal** - I cannot run interactive curses apps
2. **May have npyscreen quirks** - Event handling behavior might differ from expectations
3. **Status bar drawing** - Uses direct curses calls, may conflict with npyscreen

## What Should Happen (Theory)

When you run:
```bash
python3 mbasic --ui curses test_continue.bas
```

1. Set breakpoint: Press 'b' on line 20 → See ●
2. Run: Press Ctrl+R
3. Execution starts in `_execution_timer()`
4. Hits line 20 → Returns status 'breakpoint'
5. Sets `paused_at_breakpoint = True`
6. Shows status bar: "BREAKPOINT at line 20 - Press C/S/E"
7. Returns to npyscreen event loop
8. User presses 'c':
   - `h_breakpoint_key()` called with ord('c')
   - Checks `paused_at_breakpoint` → True
   - Calls `_handle_breakpoint_continue()`
   - Removes breakpoint, sets paused = False
   - Calls `_execution_timer()` to resume
9. Program continues and completes

## Potential Issues

1. **npyscreen handler return values** - Not sure if returning False actually lets keys pass through
2. **Status bar conflicts** - Direct curses drawing might not work well with npyscreen
3. **Event loop recursion** - `_execution_timer()` calls itself, might cause issues
4. **Window references** - `form.editor.parent` might not be the right window

## What You Need to Test

1. Does 'b' toggle breakpoint (● appears/disappears)?
2. Does Ctrl+R start execution?
3. Does it pause at breakpoint?
4. Does status bar show at bottom?
5. Does 'c' continue?
6. Does 's' step?
7. Does 'e' end?
8. Can you type 's' in editor when not paused?

## If It Doesn't Work

The most likely issues:
1. **Status bar not visible** - Try checking what `_update_status()` actually does
2. **Keys don't work at breakpoint** - Check if `h_breakpoint_key()` is being called
3. **Keys always captured** - Form handlers might not respect False return value
4. **Screen blanks** - npyscreen and direct curses don't mix well

## Alternative If This Fails

If the current approach doesn't work:
1. Remove status bar updates
2. Just add breakpoint messages to output window
3. Auto-continue through breakpoints
4. Use breakpoints as "logging points" not "pause points"

This would still be useful - you'd see "*** Breakpoint at line 20 ***" in output.

## Conclusion

I've implemented a theoretically correct breakpoint system:
- ✅ Architecture is sound
- ✅ Core interpreter works
- ❌ Full UI integration not tested

The code is complete and should work, but I cannot verify it works end-to-end without a real terminal.
