"""File validation utilities for image uploads."""

import magic
from fastapi import HTTPException, UploadFile, status

# Maximum file size: 50MB
MAX_FILE_SIZE = 52_428_800

# Allowed MIME types
ALLOWED_MIME_TYPES = {
    "image/jpeg",
    "image/jpg",
    "image/png",
    "image/gif",
    "image/webp",
    "image/svg+xml",
}

# Allowed file extensions
ALLOWED_EXTENSIONS = {".jpg", ".jpeg", ".png", ".gif", ".webp", ".svg"}


async def validate_image_file(file: UploadFile) -> bytes:
    """
    Validate uploaded image file.

    Checks:
    - File size within limits
    - MIME type allowed
    - Magic bytes match declared type
    - File extension valid

    Args:
        file: The uploaded file from FastAPI

    Returns:
        File contents as bytes

    Raises:
        HTTPException: If validation fails
    """
    # Read file contents
    contents = await file.read()
    file_size = len(contents)

    # Reset file pointer for potential re-reading
    await file.seek(0)

    # Check file size
    if file_size == 0:
        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Empty file uploaded")

    if file_size > MAX_FILE_SIZE:
        raise HTTPException(
            status_code=status.HTTP_413_REQUEST_ENTITY_TOO_LARGE,
            detail=f"File too large. Maximum size is {MAX_FILE_SIZE / 1_048_576:.1f}MB",
        )

    # Validate file extension
    if file.filename:
        extension = "." + file.filename.lower().split(".")[-1] if "." in file.filename else ""
        if extension not in ALLOWED_EXTENSIONS:
            raise HTTPException(
                status_code=status.HTTP_400_BAD_REQUEST,
                detail=f"Invalid file extension. Allowed: {', '.join(ALLOWED_EXTENSIONS)}",
            )

    # Detect actual MIME type using magic bytes
    mime = magic.from_buffer(contents, mime=True)

    # Validate MIME type
    if mime not in ALLOWED_MIME_TYPES:
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail=f"Invalid file type '{mime}'. Allowed types: {', '.join(ALLOWED_MIME_TYPES)}",
        )

    return contents


def sanitize_filename(filename: str) -> str:
    """
    Sanitize filename to prevent path traversal and other attacks.

    Args:
        filename: Original filename

    Returns:
        Sanitized filename
    """
    import re

    # Remove path separators
    filename = filename.replace("/", "_").replace("\\", "_")

    # Remove any non-alphanumeric characters except dots, dashes, underscores
    filename = re.sub(r"[^a-zA-Z0-9._-]", "_", filename)

    # Limit length
    max_length = 255
    if len(filename) > max_length:
        # Keep extension
        parts = filename.rsplit(".", 1)
        if len(parts) == 2:
            name, ext = parts
            filename = name[: max_length - len(ext) - 1] + "." + ext
        else:
            filename = filename[:max_length]

    return filename