"""This module contains image validation methods."""

from PIL import Image
from PIL import UnidentifiedImageError
from src.common.constants import errors
from src.common.lambda_exceptions import LambdaStatusError
from src.constants import image_standards


class InvalidImageError(LambdaStatusError):
    """Exception class for image validation errors."""

    def __init__(self, code, msg=None):
        """Initialize instance."""
        LambdaStatusError.__init__(
            self,
            error_code=code,
            error_params={'message': msg}
        )


class InvalidImageColor(InvalidImageError):
    """Exception class for invalid image color."""


class InvalidImageDimensions(InvalidImageError):
    """Exception class for invalid image dimensions."""


def validate_image(file_contents):
    """Validate the contents of an image.

    Args:
        file_contents (io.BytesIO): Image file contents.

    Returns:
        bool: True if validation is successful.
    Raises:
        Exception: If a validation fails.
    """
    try:
        file_contents.seek(0)
        image = Image.open(file_contents)

        if not validate_mode(image.mode):
            raise InvalidImageColor(errors.IMAGE_INVALID_MODE_CODE, image.mode)

        length, width = image.size
        validation_result = validate_dimensions(length, width)
        if validation_result != image_standards.VALID_DIMENSIONS_CODE:
            raise InvalidImageDimensions(validation_result)
        return True
    except UnidentifiedImageError:
        raise InvalidImageError(errors.IMAGE_INVALID_FILE_CODE, 'it can not be identified by PIL.')


def validate_dimensions(width, height):
    """Check image dimensions for cover images.

    Args:
        width (int): Image width.
        height (int): Image height.

    Returns:
        str: The result of image dimensions validation.
             Error code in case of an error

    """
    if width != height:
        return errors.IMAGE_WRONG_ASPECT_RATIO_CODE
    if width < image_standards.MIN_IMAGE_DIMENSION:
        return errors.IMAGE_TOO_SMALL_DIMENSIONS_CODE
    if width > image_standards.MAX_IMAGE_DIMENSION:
        return errors.IMAGE_TOO_LARGE_DIMENSIONS_CODE
    return image_standards.VALID_DIMENSIONS_CODE


def validate_mode(mode):
    """Check image mode.

    https://pillow.readthedocs.io/en/5.2.x/handbook/concepts.html#concept-modes

    Args:
        mode (str): image mode value

    Returns:
        bool: True if mode is valid, False otherwise
    """
    return mode in image_standards.VALID_MODES