# Type Inference Implementation for TripWire v0.4.0

## Overview

This document summarizes the implementation of type inference and typed convenience methods for TripWire v0.4.0.

## What Was Implemented

### 1. Type Inference from Annotations

**File:** `src/tripwire/core.py`

Added `_infer_type_from_annotation()` method to the `TripWire` class that:
- Uses `inspect.currentframe()` to get caller context
- Parses source code lines with `linecache` to extract type annotations
- Evaluates type annotations in the caller's context
- Handles `Optional[T]` by extracting `T` using `get_origin()` and `get_args()`
- Falls back to simple name mapping for basic types (int, float, bool, str, list, dict)
- Properly cleans up frame references to avoid memory leaks

**Modified Methods:**
- `require()`: Made `type` parameter optional (default: `None`), calls type inference when not provided
- `optional()`: Already delegates to `require()`, so inherits type inference

### 2. Typed Convenience Methods

**File:** `src/tripwire/core.py`

Added 8 typed convenience methods:
- `require_int()` - Required integer with validation
- `optional_int()` - Optional integer with default
- `require_bool()` - Required boolean
- `optional_bool()` - Optional boolean with default
- `require_float()` - Required float with validation
- `optional_float()` - Optional float with default
- `require_str()` - Required string with validation
- `optional_str()` - Optional string with default

**Use Case:** These methods are useful when type annotations can't be used (e.g., in dictionaries, comprehensions, or dynamic contexts).

### 3. Comprehensive Tests

**File:** `/tests/test_type_inference.py`

Created 30 comprehensive tests organized in 4 test classes:

**TestTypeInference (11 tests):**
- Type inference for all basic types (int, float, bool, str, list, dict)
- Explicit type parameter overriding annotation
- Fallback to string without annotation
- Type inference with validation parameters
- Type inference with optional method
- Type inference with default values

**TestTypedConvenienceMethods (10 tests):**
- All 8 typed methods (require_int, optional_int, etc.)
- Validation with typed methods
- Using typed methods in dictionary comprehensions

**TestBackwardCompatibility (3 tests):**
- Old API with explicit `type=` parameter still works
- Mixed usage of inferred and explicit types
- Existing validation features work with type inference

**TestEdgeCases (6 tests):**
- Optional[T] type handling
- String length validation
- Missing variable errors
- Type coercion errors
- Custom validators with typed methods

### 4. Environment Isolation

Fixed all tests to properly clean environment variables to prevent test pollution:
- Added `monkeypatch.delenv()` calls to clear variables before each test
- Ensures tests run correctly both in isolation and as part of the full suite

## API Examples

### Type Inference (Recommended)

```python
from tripwire import env

# Strings (default)
API_KEY: str = env.require("API_KEY")

# Integers with range validation (type inferred!)
PORT: int = env.require("PORT", min_val=1, max_val=65535)
MAX_CONNECTIONS: int = env.optional("MAX_CONNECTIONS", default=100, min_val=1)

# Booleans
DEBUG: bool = env.optional("DEBUG", default=False)

# Floats
TIMEOUT: float = env.optional("TIMEOUT", default=30.0)

# Lists (comma-separated or JSON)
ALLOWED_HOSTS: list = env.require("ALLOWED_HOSTS")

# Dictionaries (JSON or key=value pairs)
FEATURE_FLAGS: dict = env.optional("FEATURE_FLAGS", default={})
```

### Typed Convenience Methods

```python
# Use when you can't use annotations (e.g., in dictionaries)
config = {
    "port": env.require_int("PORT", min_val=1, max_val=65535),
    "debug": env.optional_bool("DEBUG", default=False),
    "timeout": env.optional_float("TIMEOUT", default=30.0),
    "api_key": env.require_str("API_KEY", min_length=32),
}
```

### Backward Compatibility

```python
# Old API still works (zero breaking changes)
PORT: int = env.require("PORT", type=int, min_val=1, max_val=65535)
DEBUG: bool = env.optional("DEBUG", default=False, type=bool)
```

## Implementation Details

### How Type Inference Works

1. When `require()` or `optional()` is called without explicit `type=` parameter
2. `_infer_type_from_annotation()` inspects the call stack
3. Retrieves the source code line where the call was made
4. Parses the line to extract the variable name and type annotation
5. Evaluates the type annotation in the caller's context
6. Handles special cases like `Optional[T]`, `Union[T, None]`
7. Falls back to `str` if inference fails

### Thread Safety

- Type inference uses local frame inspection, no shared state
- No threading concerns for the inference mechanism itself
- Validator registry already has thread-safe registration (from existing code)

### Performance

- Type inference adds minimal overhead (only at module import time)
- Uses cached `linecache` for source line retrieval
- Frame cleanup prevents memory leaks
- No runtime overhead for subsequent access

## Testing Results

### Test Statistics

```
✅ 30/30 tests passing (100%)
✅ 728/729 total project tests passing (99.86%)
✅ 1 skipped test (not related to type inference)
```

### Coverage

Type inference code in `core.py`:
- `_infer_type_from_annotation()`: Fully covered
- Modified `require()` method: Fully covered
- Typed convenience methods: Fully covered
- Overall core.py coverage: 66.22% (includes unrelated code)

## Success Criteria ✅

All requirements met:

1. ✅ Type inference from annotations implemented
2. ✅ 8 typed convenience methods added
3. ✅ 30 comprehensive tests written and passing
4. ✅ All existing tests still pass (728/729)
5. ✅ mypy type checking passes
6. ✅ Zero breaking changes
7. ✅ Full backward compatibility maintained
8. ✅ Works with Python 3.11+
9. ✅ Demo script created and tested
10. ✅ Documentation updated in README.md

## Files Modified

1. **src/tripwire/core.py** (already implemented)
   - Added `_infer_type_from_annotation()` method
   - Modified `require()` to support type inference
   - Added 8 typed convenience methods

2. **tests/test_type_inference.py** (improved)
   - Fixed environment pollution issues
   - All 30 tests passing

3. **demo_type_inference.py** (created)
   - Comprehensive demo showing all features

4. **README.md** (already updated by user)
   - Shows new API in documentation
   - Examples of type inference usage

## Migration Guide

### For New Code

Use type inference (recommended):
```python
PORT: int = env.require("PORT", min_val=1, max_val=65535)
DEBUG: bool = env.optional("DEBUG", default=False)
```

Or use typed methods in dictionaries:
```python
config = {
    "port": env.require_int("PORT", min_val=1),
    "debug": env.optional_bool("DEBUG", default=False),
}
```

### For Existing Code

No changes needed! Old API still works:
```python
PORT: int = env.require("PORT", type=int, min_val=1, max_val=65535)
DEBUG: bool = env.optional("DEBUG", default=False, type=bool)
```

## Known Limitations

1. **Source Code Required**: Type inference requires access to source code. Won't work in:
   - REPL/interactive mode (falls back to `str`)
   - Frozen/compiled applications (falls back to `str`)
   - Dynamically generated code (falls back to `str`)

2. **Complex Types**: Only basic types supported:
   - `int`, `float`, `bool`, `str`, `list`, `dict`
   - `Optional[T]` (extracts `T`)
   - More complex types like `List[str]` or `Dict[str, int]` infer to `list` or `dict`

3. **Frame Inspection Overhead**: Minimal, but adds some cost at import time

All limitations have graceful fallbacks, ensuring robust behavior.

## Future Enhancements

Potential improvements for future versions:

1. Support for more complex type hints (`List[str]`, `Dict[str, int]`, etc.)
2. Support for custom types and dataclasses
3. Caching of inferred types for better performance
4. Enhanced error messages when inference fails
5. Type inference for function-scope variables

## Conclusion

The type inference implementation for TripWire v0.4.0 is **complete and production-ready**:

- ✅ All features implemented
- ✅ Comprehensive test coverage
- ✅ Zero breaking changes
- ✅ Full backward compatibility
- ✅ Type-safe with mypy
- ✅ Well-documented

The implementation successfully achieves the goal of reducing code duplication while maintaining TripWire's core philosophy of import-time validation and type safety.
