import os
import imghdr
from io import BytesIO

import cv2
import khandy
import numpy as np
from PIL import Image


def imread_pil(file_or_buffer, formats=None):
    """Improvement on Image.open to avoid ResourceWarning.
    """
    try:
        if isinstance(file_or_buffer, bytes):
            buffer = BytesIO()
            buffer.write(file_or_buffer)
            buffer.seek(0)
            image = Image.open(buffer)
        elif hasattr(file_or_buffer, 'read'):
            image = Image.open(file_or_buffer)
        else:
            # open path as file to avoid ResourceWarning (https://github.com/python-pillow/Pillow/issues/835)
            with open(file_or_buffer, 'rb') as f:
                image = Image.open(f)
        return image
    except Exception as e:
        print(e)
        return None
        

def imread_cv(file_or_buffer, flags=-1):
    """Improvement on cv2.imread, make it support filename including chinese character.
    """
    try:
        if isinstance(file_or_buffer, bytes):
            return cv2.imdecode(np.frombuffer(file_or_buffer, dtype=np.uint8), flags)
        else:
            # support type: file or str or Path
            return cv2.imdecode(np.fromfile(file_or_buffer, dtype=np.uint8), flags)
    except Exception as e:
        print(e)
        return None
    
    
def imwrite_cv(filename, image, params=None):
    """Improvement on cv2.imwrite, make it support filename including chinese character.
    """
    cv2.imencode(os.path.splitext(filename)[-1], image, params)[1].tofile(filename)
    

def imwrite_bytes(filename, image_bytes, update_extension=True):
    extension = imghdr.what('', image_bytes)
    if extension is None:
        raise ValueError('image_bytes is not image')
    extension = '.' + extension
    file_extension = khandy.get_path_extension(filename)
    if extension.lower() != file_extension.lower():
        if update_extension:
            filename = khandy.replace_path_extension(filename, extension)
        else:
            image = cv2.imdecode(np.frombuffer(image_bytes, np.uint8), -1)
            image_bytes = cv2.imencode(file_extension, image)[1]
    with open(filename, "wb") as f:
        f.write(image_bytes)
    return filename


def normalize_image_dtype(image, keep_num_channels=False):
    """Normalize image dtype to uint8 (usually for visualization).
    
    Args:
        image : ndarray
            Input image.
        keep_num_channels : bool, optional
            If this is set to True, the result is an array which has 
            the same shape as input image, otherwise the result is 
            an array whose channels number is 3.
            
    Returns:
        out: ndarray
            Image whose dtype is np.uint8.
    """
    assert (image.ndim == 3 and image.shape[-1] in [1, 3]) or (image.ndim == 2)

    image = image.astype(np.float32)
    image = khandy.minmax_normalize(image, axis=None, copy=False)
    image = np.array(image * 255, dtype=np.uint8)
    
    if not keep_num_channels:
        if image.ndim == 2:
            image = np.expand_dims(image, -1)
        if image.shape[-1] == 1:
            image = np.tile(image, (1,1,3))
    return image
    
    
def normalize_image_shape(image, swap_rb=False):
    """Normalize image shape to (h, w, 3).
    
    Args:
        image : ndarray
            Input image.
        swap_rb : bool, optional
            whether swap red and blue channel or not
            
    Returns:
        out: ndarray
            Image whose shape is (h, w, 3).
    """
    if image.ndim == 2:
        image = cv2.cvtColor(image, cv2.COLOR_GRAY2BGR)
    elif image.ndim == 3:
        num_channels = image.shape[-1]
        if num_channels == 1:
            image = cv2.cvtColor(image, cv2.COLOR_GRAY2BGR)
        elif num_channels == 3:
            if swap_rb:
                image = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)
        elif num_channels == 4:
            if swap_rb:
                image = cv2.cvtColor(image, cv2.COLOR_BGRA2RGB)
            else:
                image = cv2.cvtColor(image, cv2.COLOR_BGRA2BGR)
        else:
            raise ValueError('Unsupported!')
    else:
        raise ValueError('Unsupported!')
    return image


def stack_image_list(image_list, dtype=np.float32):
    """Join a sequence of image along a new axis before first axis.

    References:
        `im_list_to_blob` in `py-faster-rcnn-master/lib/utils/blob.py`
    """
    assert isinstance(image_list, (tuple, list))

    max_dimension = np.array([image.ndim for image in image_list]).max()
    assert max_dimension in [2, 3]
    max_shape = np.array([image.shape[:2] for image in image_list]).max(axis=0)
    
    num_channels = []
    for image in image_list:
        if image.ndim == 2:
            num_channels.append(1)
        else:
            num_channels.append(image.shape[-1])
    assert len(set(num_channels) - set([1])) in [0, 1]
    max_num_channels = np.max(num_channels)
    
    blob = np.empty((len(image_list), max_shape[0], max_shape[1], max_num_channels), dtype=dtype)
    for k, image in enumerate(image_list):
        blob[k, :image.shape[0], :image.shape[1], :] = np.atleast_3d(image).astype(dtype, copy=False)
    if max_dimension == 2:
        blob = np.squeeze(blob, axis=-1)
    return blob
    

def is_numpy_image(image):
    return isinstance(image, np.ndarray) and image.ndim in {2, 3}


def is_gray_image(image, tol=3):
    assert is_numpy_image(image)
    if image.ndim == 2:
        return True
    elif image.ndim == 3:
        num_channels = image.shape[-1]
        if num_channels == 1:
            return True
        elif num_channels == 4:
            rgb = cv2.cvtColor(image, cv2.COLOR_BGRA2BGR)
            gray = cv2.cvtColor(rgb, cv2.COLOR_BGR2GRAY)
            gray3 = cv2.cvtColor(gray, cv2.COLOR_GRAY2BGR)
            mae = np.mean(cv2.absdiff(rgb, gray3))
            return mae <= tol
        elif num_channels == 3:
            gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
            gray3 = cv2.cvtColor(gray, cv2.COLOR_GRAY2BGR)
            mae = np.mean(cv2.absdiff(image, gray3))
            return mae <= tol
        else:
            return False
    else:
        return False