# Phase 1: I/O Abstraction - COMPLETE ✅

**Date**: 2025-10-24
**Status**: COMPLETE ✅ - All testing passed

## Summary

Successfully completed the core infrastructure for I/O abstraction layer, enabling the MBASIC interpreter to work with different I/O backends (console, GUI, embedded).

## Completed Work

### 1. I/O Abstraction Layer (src/io/) ✅

**Created three modules:**

- **src/io/base.py** - IOHandler abstract interface (140 lines)
  - `output(text, end)` - Output text to user
  - `input(prompt)` - Input text from user
  - `input_line(prompt)` - LINE INPUT statement
  - `input_char(blocking)` - INKEY$, INPUT$ single character
  - `clear_screen()` - CLS statement
  - `error(message)` - Error message output
  - `debug(message)` - Debug output
  - `locate(row, col)` - LOCATE cursor positioning
  - `get_cursor_position()` - Get cursor position

- **src/io/console.py** - ConsoleIOHandler for CLI (145 lines)
  - Uses Python `input()` and `print()` functions
  - Platform-specific `input_char()` for Unix/Windows
  - ANSI escape codes for cursor positioning
  - Optional debug mode (controlled by `debug_enabled` flag)

- **src/io/gui.py** - GUIIOHandler stub for visual UIs (140 lines)
  - Stub implementation showing interface usage
  - Internal buffers for testing
  - Helper methods: `get_output()`, `queue_input()`
  - Extensive documentation for visual UI developers

**Total**: 425 lines of new code

### 2. Interpreter Refactoring ✅

**Modified src/interpreter.py** to use IOHandler:

- Added `io_handler` parameter to `Interpreter.__init__()`
- Defaults to `ConsoleIOHandler()` if not provided
- **Converted 36 I/O calls:**
  - 34 `print()` calls → `self.io.output()` or `self.io.debug()`
  - 2 `input()` calls → `self.io.input()`

**Affected areas:**
- PRINT statement output
- PRINT USING output
- INPUT statement prompts and input
- LINE INPUT prompts and input
- Break messages (Ctrl+C)
- STOP statement messages
- TRON trace output
- FILES command output
- SYSTEM command output
- Debug logging (now respects debug_enabled flag)

### 3. Runtime Inspection Methods ✅

**Added three inspection methods to src/runtime.py** (76 lines):

- **`get_all_variables()`** - Export all variables with values
  ```python
  {'A': 42, 'B$': 'HELLO', 'C#': 3.14, 'D(': [1,2,3], 'FNA': '<DEF FN FNA>'}
  ```
  - Includes scalars, arrays (with '(' suffix), and DEF FN functions

- **`get_gosub_stack()`** - Export GOSUB call stack
  ```python
  [100, 500, 1000]  # Called GOSUB at lines 100, 500, 1000
  ```
  - Ordered from oldest to newest (bottom to top)

- **`get_for_loop_stack()`** - Export FOR loop information
  ```python
  [{'var': 'I', 'current': 5, 'end': 10, 'step': 1, 'line': 100}]
  ```

## Architecture Benefits

### Backward Compatibility ✅
- Interpreter defaults to ConsoleIOHandler if no io_handler provided
- Existing code (InteractiveMode, mbasic) continues to work without changes
- All print()/input() behavior preserved

### Visual UI Support ✅
- Clean IOHandler interface for custom I/O backends
- Full state inspection (variables, stacks, loops)
- No modifications to core interpreter logic required

### Testability ✅
- GUIIOHandler stub can be used for testing
- `get_output()` and `queue_input()` for automated tests
- Mock I/O handlers can verify output without console

## Additional Work Completed

### 4. InteractiveMode Update ✅
- Added `io_handler` parameter to `InteractiveMode.__init__()`
- Updated 3 Interpreter instantiations to pass `self.io`
- Backward compatible (defaults to ConsoleIOHandler)

### 5. Module Naming Fix ✅
- **Problem**: Naming conflict with Python's built-in `io` module
- **Solution**: Renamed `src/io/` → `src/iohandler/`
- Updated all imports to use `iohandler.console`
- Added note in `__init__.py` about rename

### 6. Testing ✅
All tests passed successfully:
- ✅ `tests/test_deffn.bas` - DEF FN functionality
- ✅ `test_fn_shadow.bas` - Parameter shadowing
- ✅ `test_fn_shadow2.bas` - Global variable access in functions
- ✅ DEBUG mode - Debug output works correctly

## Deferred to Future Phases
- **Stepping and Breakpoint Support** - Add to Interpreter class
  - `step_line()`, `step_statement()`, `step_expression()`
  - `set_breakpoint()`, `clear_breakpoint()`
  - ExecutionState class with breakpoints set
  - This can be added later without breaking existing code
  - Deferred to Phase 2 or 3

## Git Commits

1. **88f0081** - Add I/O abstraction layer (Phase 1 part 1/3)
   - Created src/io/ module with IOHandler, ConsoleIOHandler, GUIIOHandler

2. **d82acc0** - Refactor Interpreter to use IOHandler (Phase 1 part 2/3)
   - Modified interpreter.py: 36 I/O calls converted

3. **e1851c4** - Add inspection methods to Runtime (Phase 1 part 3/3)
   - Added get_all_variables(), get_gosub_stack(), get_for_loop_stack()

4. **2d9ecf5** - Update InteractiveMode to pass IOHandler to Interpreter
   - Added io_handler parameter, updated 3 instantiations

5. **8c2c076** - Fix module naming conflict: io → iohandler
   - Renamed directory to avoid Python built-in conflict
   - All tests pass

## Statistics

**Lines Added**: ~540 lines
- src/io/: 425 lines (new)
- src/runtime.py: +76 lines (inspection methods)
- src/interpreter.py: +6 lines, modified 36 I/O calls

**Files Modified**: 2 files
**Files Created**: 4 files (io/__init__.py, base.py, console.py, gui.py)

**Time Spent**: ~2 hours

## Next Steps

### Immediate (Complete Phase 1)
1. Update InteractiveMode to pass IOHandler
2. Test existing programs (test_deffn.bas, etc.)
3. Mark Phase 1 as complete

### Future Phases
- **Phase 2**: Extract program management from InteractiveMode
- **Phase 3**: Create UIBackend interface
- **Phase 4**: Add dynamic backend loading (importlib)
- **Phase 5**: Evaluate mobile frameworks (deferred)

## Conclusion

**Phase 1 is COMPLETE** ✅✅✅

All planned work finished and tested successfully:
- ✅ I/O abstraction layer implemented (src/iohandler/)
- ✅ Interpreter refactored to use IOHandler
- ✅ Runtime inspection methods added
- ✅ InteractiveMode updated to pass IOHandler
- ✅ Module naming conflict resolved
- ✅ All tests pass

The interpreter can now work with any I/O backend without modification. Visual UI developers can:
- Subclass IOHandler for custom I/O (console, GUI, mobile, embedded)
- Use get_all_variables() to display variable table in real-time
- Use get_gosub_stack() to show GOSUB call stack
- Use get_for_loop_stack() to show FOR loop state
- Pass custom IOHandler to InteractiveMode() or Interpreter()

**Ready for Phase 2**: Program management extraction
