"""File validation utilities"""
import magic
import os
from fastapi import UploadFile, HTTPException
from typing import Set, Dict
import logging

from app.core.config import get_settings

logger = logging.getLogger(__name__)
settings = get_settings()

# MIME type whitelists
IMAGE_TYPES: Set[str] = {
    "image/jpeg",
    "image/png",
    "image/gif"
}

DOCUMENT_TYPES: Set[str] = {
    "application/pdf",
    "application/x-pdf",  # Some systems detect PDF as x-pdf
}

# Extensions that can be accepted even if MIME detection fails
EXTENSION_FALLBACK: Dict[str, str] = {
    ".pdf": "application/pdf",
    ".doc": "application/msword",
    ".docx": "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
}

LOG_TYPES: Set[str] = {
    "text/plain",
    "text/csv"
}


def detect_mime_type(file_data: bytes) -> str:
    """
    Detect MIME type from file content using python-magic

    Args:
        file_data: First chunk of file data

    Returns:
        MIME type string
    """
    try:
        mime = magic.Magic(mime=True)
        return mime.from_buffer(file_data)
    except Exception as e:
        logger.error(f"Failed to detect MIME type: {e}")
        return "application/octet-stream"


def validate_file_type(file: UploadFile, allowed_types: Set[str]) -> str:
    """
    Validate file MIME type using actual file content

    Args:
        file: FastAPI UploadFile object
        allowed_types: Set of allowed MIME types

    Returns:
        Detected MIME type

    Raises:
        HTTPException if file type is not allowed
    """
    # Read first 2048 bytes to detect MIME type
    file.file.seek(0)
    header = file.file.read(2048)
    file.file.seek(0)

    # Detect actual MIME type from content
    detected_mime = detect_mime_type(header)

    if detected_mime not in allowed_types:
        # Try extension fallback for known safe file types
        filename = file.filename or ""
        _, ext = os.path.splitext(filename.lower())

        if ext in EXTENSION_FALLBACK:
            logger.info(
                f"MIME detection returned {detected_mime} for {filename}, "
                f"using extension fallback: {EXTENSION_FALLBACK[ext]}"
            )
            return EXTENSION_FALLBACK[ext]

        raise HTTPException(
            status_code=400,
            detail=f"File type not allowed: {detected_mime}. Allowed types: {', '.join(allowed_types)}"
        )

    return detected_mime


def validate_file_size(file: UploadFile, max_size: int):
    """
    Validate file size

    Args:
        file: FastAPI UploadFile object
        max_size: Maximum allowed size in bytes

    Raises:
        HTTPException if file exceeds max size
    """
    # Seek to end to get file size
    file.file.seek(0, 2)  # 2 = SEEK_END
    file_size = file.file.tell()
    file.file.seek(0)  # Reset to beginning

    if file_size > max_size:
        max_mb = max_size / (1024 * 1024)
        actual_mb = file_size / (1024 * 1024)
        raise HTTPException(
            status_code=413,
            detail=f"File size exceeds limit: {actual_mb:.2f}MB > {max_mb:.2f}MB"
        )

    return file_size


def get_file_type_and_limits(mime_type: str) -> tuple[str, int]:
    """
    Determine file type category and size limit from MIME type

    Args:
        mime_type: MIME type string

    Returns:
        Tuple of (file_type, max_size)

    Raises:
        HTTPException if MIME type not recognized
    """
    # Include extension fallback types as documents
    document_types_extended = DOCUMENT_TYPES | set(EXTENSION_FALLBACK.values())

    if mime_type in IMAGE_TYPES:
        return ("image", settings.get_image_max_size_bytes())
    elif mime_type in document_types_extended:
        return ("document", settings.get_document_max_size_bytes())
    elif mime_type in LOG_TYPES:
        return ("log", settings.get_log_max_size_bytes())
    else:
        raise HTTPException(
            status_code=400,
            detail=f"Unsupported file type: {mime_type}"
        )


def validate_upload_file(file: UploadFile) -> tuple[str, str, int]:
    """
    Validate uploaded file (type and size)

    Args:
        file: FastAPI UploadFile object

    Returns:
        Tuple of (file_type, mime_type, file_size)

    Raises:
        HTTPException if validation fails
    """
    # Combine all allowed types
    all_allowed_types = IMAGE_TYPES | DOCUMENT_TYPES | LOG_TYPES

    # Validate MIME type
    mime_type = validate_file_type(file, all_allowed_types)

    # Get file type category and max size
    file_type, max_size = get_file_type_and_limits(mime_type)

    # Validate file size
    file_size = validate_file_size(file, max_size)

    return (file_type, mime_type, file_size)