src/cleaners/encoding_cleaner.py

"""
Encoding detection and normalization for text files.

Handles the messy reality of 20 years of web-generated data with
mixed encodings, mojibake, and partial writes containing null bytes.
"""

from pathlib import Path
from typing import Optional, Tuple, List
import chardet
import ftfy

from ..core.base_classes import BaseCleaner
from ..core.config import Config
from ..core.errata_logger import ErrataLogger
from ..core.exceptions import EncodingError


class EncodingCleaner(BaseCleaner):
    """
    Detects and normalizes file encodings.

    Handles:
    - Automatic encoding detection using chardet
    - Fallback to candidate encodings
    - Mojibake correction using ftfy
    - Null byte removal from partial writes
    - Normalization to UTF-8
    """

    def __init__(self, config: Config, errata_logger: Optional[ErrataLogger] = None):
        """
        Initialize encoding cleaner.

        Args:
            config: Configuration object
            errata_logger: Optional errata logger for error tracking
        """
        super().__init__(config, errata_logger)

        # Get configuration
        self.candidate_encodings: List[str] = config.get(
            'encoding.candidate_encodings',
            ['utf-8', 'latin-1', 'windows-1252', 'iso-8859-1']
        )
        self.confidence_threshold: float = config.get(
            'encoding.confidence_threshold',
            0.7
        )
        self.fix_mojibake: bool = config.get('encoding.fix_mojibake', True)

    def detect_encoding(
        self,
        file_path: str | Path,
        sample_size: int = 100000
    ) -> Tuple[str, float]:
        """
        Detect file encoding using chardet.

        Args:
            file_path: Path to file
            sample_size: Number of bytes to sample for detection

        Returns:
            Tuple of (encoding, confidence)

        Raises:
            EncodingError: If encoding cannot be detected
        """
        file_path = Path(file_path)

        try:
            with open(file_path, 'rb') as f:
                raw_data = f.read(sample_size)

            # Remove null bytes before detection
            raw_data = raw_data.replace(b'\x00', b'')

            if not raw_data:
                raise EncodingError(f"File is empty or contains only null bytes: {file_path}")

            result = chardet.detect(raw_data)
            encoding = result['encoding']
            confidence = result['confidence']

            if encoding is None:
                raise EncodingError(f"Could not detect encoding for {file_path}")

            return encoding, confidence

        except IOError as e:
            raise EncodingError(f"Failed to read file {file_path}: {e}")

    def read_with_encoding(
        self,
        file_path: str | Path,
        encoding: str,
        remove_null_bytes: bool = True
    ) -> str:
        """
        Read file with specified encoding.

        Args:
            file_path: Path to file
            encoding: Encoding to use
            remove_null_bytes: Whether to remove null bytes

        Returns:
            Decoded text content

        Raises:
            EncodingError: If reading with encoding fails
        """
        file_path = Path(file_path)

        try:
            with open(file_path, 'rb') as f:
                raw_data = f.read()

            # Remove null bytes from partial writes
            if remove_null_bytes:
                raw_data = raw_data.replace(b'\x00', b'')

            # Decode with specified encoding
            text = raw_data.decode(encoding, errors='strict')
            return text

        except UnicodeDecodeError as e:
            raise EncodingError(
                f"Failed to decode {file_path} with {encoding}: {e}"
            )
        except IOError as e:
            raise EncodingError(f"Failed to read file {file_path}: {e}")

    def clean(
        self,
        data: str | Path,
        file_path: Optional[str] = None,
        **kwargs
    ) -> str:
        """
        Clean encoding of text data or file.

        Args:
            data: Either file path or text string to clean
            file_path: Optional file path for error logging
            **kwargs: Additional parameters

        Returns:
            Cleaned UTF-8 text

        Raises:
            EncodingError: If encoding cannot be resolved
        """
        # If data is a path, read the file
        if isinstance(data, (str, Path)) and Path(data).is_file():
            file_path = str(data)
            data, was_utf8 = self._read_file_smart_tagged(Path(data))
        elif not isinstance(data, str):
            raise EncodingError(f"Invalid data type: {type(data)}")
        else:
            was_utf8 = False

        # Fast path: if file decoded as UTF-8, skip ftfy and round-trip
        # Normalize all line endings: CRLF -> LF, then bare CR -> LF
        # (some files have mixed line endings, e.g. card190309.dat, loc020520.dat)
        if was_utf8:
            return data.replace('\r\n', '\n').replace('\r', '\n')

        # Slow path: fix mojibake and normalize
        if self.fix_mojibake:
            try:
                data = ftfy.fix_text(data)
            except Exception as e:
                self.log_error(
                    'mojibake_fix_failed',
                    f"Failed to fix mojibake: {e}",
                    file_path=file_path
                )

        # Normalize to UTF-8, logging any characters that get replaced
        encoded = data.encode('utf-8', errors='replace')
        replacement_count = encoded.count(b'\xef\xbf\xbd')  # UTF-8 bytes of U+FFFD
        if replacement_count > 0:
            self.log_error(
                'utf8_replacement_chars',
                f"{replacement_count} character(s) replaced with U+FFFD during UTF-8 normalization",
                file_path=file_path
            )
        data = encoded.decode('utf-8')

        # Normalize line endings (same as fast path)
        data = data.replace('\r\n', '\n').replace('\r', '\n')

        return data

    def _read_file_smart_tagged(self, file_path: Path) -> Tuple[str, bool]:
        """
        Read file and return (text, was_utf8).

        When was_utf8=True, the file decoded cleanly as UTF-8 and the caller
        can skip expensive ftfy/mojibake processing (just strip CR).
        """
        try:
            with open(file_path, 'rb') as f:
                raw_data = f.read()
            raw_data = raw_data.replace(b'\x00', b'')
            if not raw_data:
                raise EncodingError(f"File is empty or contains only null bytes: {file_path}")
            try:
                return raw_data.decode('utf-8'), True
            except UnicodeDecodeError:
                pass  # Fall through — need slow path for non-UTF-8
        except IOError:
            pass

        # Non-UTF-8 or IO error: use full smart reader
        return self._read_file_smart(file_path), False

    def _read_file_smart(self, file_path: Path) -> str:
        """
        Read file with intelligent encoding detection and fallback.

        Tries:
        1. Fast path: UTF-8 decode (covers ~99% of files)
        2. Fast fallback: latin-1 decode (covers remaining)
        3. Slow path: chardet detection (only if fast paths produce issues)

        Args:
            file_path: Path to file

        Returns:
            Decoded text

        Raises:
            EncodingError: If all attempts fail
        """
        last_error = None

        # Fast path: try UTF-8 directly, fallback to latin-1
        # Profiling shows ~99% of files are ASCII/UTF-8 compatible.
        # This avoids expensive chardet detection for the common case.
        try:
            with open(file_path, 'rb') as f:
                raw_data = f.read()
            raw_data = raw_data.replace(b'\x00', b'')
            if not raw_data:
                raise EncodingError(f"File is empty or contains only null bytes: {file_path}")
            try:
                return raw_data.decode('utf-8')
            except UnicodeDecodeError:
                return raw_data.decode('latin-1')
        except (IOError, EncodingError):
            pass  # Fall through to slow path

        # Slow path: Try automatic detection with chardet
        try:
            encoding, confidence = self.detect_encoding(file_path)

            # Skip ASCII if detected - it's too restrictive, try UTF-8 or latin-1 instead
            if encoding and encoding.lower() != 'ascii':
                if confidence >= self.confidence_threshold:
                    text = self.read_with_encoding(file_path, encoding)
                    return text
                else:
                    self.log_error(
                        'low_confidence_encoding',
                        f"Low confidence ({confidence:.2f}) for detected encoding {encoding}",
                        file_path=str(file_path)
                    )
        except EncodingError as e:
            last_error = str(e)
            self.log_error(
                'encoding_detection_failed',
                str(e),
                file_path=str(file_path)
            )

        # Try candidate encodings in order
        # Prioritize more permissive encodings for problematic files
        for encoding in self.candidate_encodings:
            try:
                text = self.read_with_encoding(file_path, encoding)
                # Log which fallback encoding worked
                if last_error:
                    self.log_error(
                        'encoding_fallback_success',
                        f"Successfully read with {encoding} after detection failed",
                        file_path=str(file_path)
                    )
                return text
            except EncodingError as e:
                last_error = str(e)
                continue

        # Last resort: latin-1 (never fails, so validate the result)
        self.log_error(
            'encoding_fallback',
            f"All encodings failed, falling back to latin-1",
            file_path=str(file_path)
        )

        try:
            text = self.read_with_encoding(file_path, 'latin-1')
        except EncodingError as e:
            raise EncodingError(
                f"Fatal: Could not read {file_path} even with latin-1: {e}"
            )

        # Sanity check: latin-1 accepts any byte sequence, so a binary/corrupt
        # file will decode without error into garbage.  Reject if the result
        # has a high ratio of control characters (excluding \t, \n, \r).
        if text:
            control_chars = sum(
                1 for ch in text
                if ch < ' ' and ch not in ('\t', '\n', '\r')
            )
            ratio = control_chars / len(text)
            if ratio > 0.05:
                self.log_error(
                    'encoding_garbage_detected',
                    f"latin-1 fallback produced {ratio:.1%} control characters — file appears corrupt",
                    file_path=str(file_path)
                )
                raise EncodingError(
                    f"File appears corrupt (latin-1 decoded to {ratio:.1%} control chars): {file_path}"
                )

        return text

    def clean_batch(
        self,
        file_paths: List[str | Path]
    ) -> List[Tuple[str, str]]:
        """
        Clean encoding for a batch of files.

        Args:
            file_paths: List of file paths to process

        Returns:
            List of tuples (file_path, cleaned_text)
        """
        results = []

        for file_path in file_paths:
            try:
                cleaned = self.clean(file_path)
                results.append((str(file_path), cleaned))
            except EncodingError as e:
                self.log_error(
                    'batch_encoding_failed',
                    str(e),
                    file_path=str(file_path)
                )
                # Continue processing other files

        return results