Add AGENTS.md for AI assistant guidance

AGENTS.md

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+# AGENTS.md - AI Assistant Guidelines for DataMorpher
+
+## Project Overview
+
+DataMorpher is a Python utility for data conversion and cleaning operations. It provides:
+- Data format conversion (CSV/JSON/Excel)
+- Data cleaning and validation
+- Report generation
+- Command-line interface
+- Streamlit web interface
+
+## Repository Structure
+
+```
+DataMorpher/
+├── datamorpher/         # Main package directory
+│   ├── __init__.py     # Package initialization
+│   ├── __main__.py     # CLI entry point  
+│   ├── cleaner.py      # Data cleaning functions
+│   ├── converter.py    # Format conversion functions
+│   ├── reporter.py     # Report generation
+│   └── streamlit_app.py # Web interface
+├── tests/              # Test directory
+├── README.md           # User documentation
+├── pyproject.toml      # Project configuration
+└── requirements.txt    # Dependencies
+```
+
+## Development Setup
+
+1. **Clone the repository**
+   ```bash
+   git clone <repository-url>
+   cd DataMorpher
+   ```
+
+2. **Install dependencies**
+   ```bash
+   pip install -r requirements.txt
+   ```
+
+3. **Install the package in development mode**
+   ```bash
+   pip install -e .
+   ```
+
+## Running Tests
+
+```bash
+# Run all tests
+pytest
+
+# Run with coverage
+pytest --cov=datamorpher
+
+# Run specific test file
+pytest tests/test_cleaner.py
+
+# Run with verbose output
+pytest -v
+```
+
+## Linting and Code Style
+
+This project uses `ruff` for linting:
+
+```bash
+# Run linter
+ruff check .
+
+# Auto-fix issues when possible
+ruff check --fix .
+
+# Check code formatting
+ruff format --check .
+
+# Format code
+ruff format .
+```
+
+## Common Commands
+
+```bash
+# Run the CLI
+python -m datamorpher --help
+
+# Convert a file
+python -m datamorpher convert input.csv output.json
+
+# Clean a dataset
+python -m datamorpher clean input.csv output.csv
+
+# Generate report
+python -m datamorpher report input.csv report.md
+
+# Run Streamlit app
+streamlit run datamorpher/streamlit_app.py
+```
+
+## Code Conventions
+
+1. **File Naming**: Use lowercase with underscores (snake_case)
+2. **Python Style**: Follow PEP 8 and maintained by ruff
+3. **Imports**: Sort imports alphabetically, stdlib first, then third-party, then local
+4. **Docstrings**: Use Google style docstrings for all public functions
+5. **Type Hints**: Use type hints for function signatures
+6. **Error Handling**: Raise appropriate exceptions with meaningful messages
+
+## Testing Guidelines
+
+1. **Test Coverage**: Aim for >90% code coverage
+2. **Test Structure**: Mirror the source structure (test_<module>.py)
+3. **Test Data**: Use minimal fixture data when possible
+4. **Mocking**: Mock external dependencies like file I/O when appropriate
+5. **Edge Cases**: Test error conditions and edge cases
+
+## Making Changes
+
+1. **Before Changes**:
+   - Read existing code to understand patterns
+   - Run tests to ensure everything is working
+   - Check current linting status
+
+2. **During Development**:
+   - Follow existing code patterns
+   - Add tests for new functionality
+   - Update docstrings and type hints
+   - Handle errors appropriately
+
+3. **Before Committing**:
+   - Run all tests: `pytest`
+   - Check linting: `ruff check .`
+   - Format code: `ruff format .`
+   - Update documentation if needed
+
+## Key Implementation Details
+
+### DataCleaner (cleaner.py)
+- Handles missing values, duplicates, data type standardization
+- Main method: `clean_data(data: pd.DataFrame) -> pd.DataFrame`
+- Validates data before cleaning
+
+### DataConverter (converter.py)
+- Converts between CSV, JSON, and Excel formats
+- Main method: `convert(input_file, output_file)`
+- Auto-detects input format, infers output from extension
+
+### Reporter (reporter.py)
+- Generates Markdown reports about datasets
+- Includes statistics, data types, missing values, samples
+- Main method: `generate_report(data) -> str`
+
+### CLI (__main__.py)
+- Uses argparse for command parsing
+- Commands: convert, clean, report
+- Handles file I/O and error reporting
+
+### Streamlit App
+- Web interface for all functionality
+- File upload/download support
+- Interactive data preview
+
+## Common Issues and Solutions
+
+1. **Import Errors**: Ensure package is installed with `pip install -e .`
+2. **File Not Found**: Use absolute paths or run from project root
+3. **Type Errors**: Check that input data matches expected format
+4. **Memory Issues**: For large files, consider chunked processing
+
+## CI/CD Considerations
+
+1. Tests must pass before merging
+2. Linting must pass (ruff)
+3. Code coverage should not decrease
+4. Documentation should be updated for new features
+
+## Important Notes
+
+- Always validate user input to prevent errors
+- Preserve data integrity during conversions
+- Provide meaningful error messages
+- Keep dependencies minimal and well-documented
+- Maintain backward compatibility