import numpy as np
from PIL import Image
import torch
import torch.nn.functional as F
from typing import List
from skimage.metrics import structural_similarity as ssim
from skimage import io, color

ROUND_DIGIT=3
NUM_ASPECT=5

TEM_SSIM_POINT_HIGH=0.9
TEM_SSIM_POINT_MID=0.75
TEM_SSIM_POINT_LOW=0.6 


class MetricSSIM_sim():
    def __init__(self) -> None: 
        """
        Initialize a class MetricSSIM_sim for testing temporal consistency of a given video.
        
        """
        None

    def evaluate(self, frame_list:List[Image.Image]):
        """
        Calculate the SSIM between adjacent frames of a given video to test temporal consistency, 
        then quantize the orginal output based on some predefined thresholds.
        
        Args:
            frame_list:List[Image.Image], frames of the video used in calculation.
            
        Returns:
            ssim_avg: float, the computed SSIM between each adjacent pair of frames and then averaged among all the pairs.
            quantized_ans: int, the quantized value of the above avg SSIM scores based on pre-defined thresholds.
        """
        
        ssim_list=[]
        for f_idx in range(len(frame_list)-1):
            frame_1=frame_list[f_idx]
            frame_1_gray=color.rgb2gray(frame_1)
            frame_2=frame_list[f_idx+1]
            frame_2_gray=color.rgb2gray(frame_2)

            ssim_value, _ = ssim(frame_1_gray, frame_2_gray, full=True,\
                                    data_range=frame_2_gray.max() - frame_2_gray.min())
            ssim_list.append(ssim_value)
        ssim_avg=np.mean(ssim_list)
        quantized_ans=0
        if ssim_avg >= TEM_SSIM_POINT_HIGH:
            quantized_ans=4
        elif ssim_avg < TEM_SSIM_POINT_HIGH and ssim_avg >= TEM_SSIM_POINT_MID:
            quantized_ans=3
        elif ssim_avg < TEM_SSIM_POINT_MID and ssim_avg >= TEM_SSIM_POINT_LOW:
            quantized_ans=2
        else:
            quantized_ans=1
        return ssim_avg, quantized_ans