"""CSV formatter for tabular output data."""

import csv
import io
from typing import Any, List, Dict
from .base_formatter import BaseFormatter


class CSVFormatter(BaseFormatter):
    """Formats data as CSV."""

    def __init__(self, flatten_nested: bool = True):
        self.flatten_nested = flatten_nested

    def format(self, data: Any) -> str:
        """Format data as CSV string."""
        if isinstance(data, list):
            return self._format_list(data)
        elif isinstance(data, dict):
            return self._format_dict(data)
        else:
            # Single value
            return str(data)

    def _format_list(self, data: List[Dict[str, Any]]) -> str:
        """Format list of dictionaries as CSV."""
        if not data:
            return ""

        # Flatten nested dictionaries if requested
        processed_data = []
        for item in data:
            if self.flatten_nested:
                processed_data.append(self._flatten_dict(item))
            else:
                processed_data.append(item)

        # Get all field names from all items
        fieldnames = set()
        for item in processed_data:
            fieldnames.update(item.keys())
        fieldnames = sorted(fieldnames)

        # Create CSV
        output = io.StringIO()
        writer = csv.DictWriter(output, fieldnames=fieldnames)
        writer.writeheader()
        writer.writerows(processed_data)

        return output.getvalue()

    def _format_dict(self, data: Dict[str, Any]) -> str:
        """Format single dictionary as CSV."""
        processed_data = self._flatten_dict(data) if self.flatten_nested else data
        fieldnames = sorted(processed_data.keys())

        output = io.StringIO()
        writer = csv.DictWriter(output, fieldnames=fieldnames)
        writer.writeheader()
        writer.writerow(processed_data)

        return output.getvalue()

    def _flatten_dict(self, data: Dict[str, Any], parent_key: str = '', sep: str = '_') -> Dict[str, Any]:
        """Flatten nested dictionaries."""
        items = []
        for key, value in data.items():
            new_key = f"{parent_key}{sep}{key}" if parent_key else key
            if isinstance(value, dict):
                items.extend(self._flatten_dict(value, new_key, sep).items())
            elif isinstance(value, list):
                # Convert lists to strings or handle each element
                if value and isinstance(value[0], (int, float, str)):
                    items.append((new_key, ','.join(map(str, value))))
                else:
                    items.append((new_key, str(value)))
            else:
                items.append((new_key, value))
        return dict(items)

    def get_file_extension(self) -> str:
        """Get file extension for CSV format."""
        return "csv"