清蒸萌新literal @[email protected]

from typing import Tuple

def relative_luminance(r :int, g :int, b :int) -> float:
    """Compute relative luminance for sRGB color

    https://www.w3.org/TR/WCAG21/#dfn-relative-luminance

    Args:
        r: red of sRGB color [0-255]
        g: green of sRGB color [0-255]
        b: blue of sRGB color [0-255]
    
    Returns:
        computed relative_luminance value defined by WCAG
    """
    R_sRGB, G_sRGB, B_sRGB = r / 255, g / 255, b / 255
    R = R_sRGB / 12.92 if R_sRGB <= 0.03928 else ((R_sRGB + 0.055) / 1.055) ** 2.4
    G = G_sRGB / 12.92 if G_sRGB <= 0.03928 else ((G_sRGB + 0.055) / 1.055) ** 2.4
    B = B_sRGB / 12.92 if B_sRGB <= 0.03928 else ((B_sRGB + 0.055) / 1.055) ** 2.4
    return 0.2126 * R + 0.7152 * G + 0.0722 * B

def contrast_ratio(color1 :Tuple[int, int, int], color2 :Tuple[int, int, int]) -> float:
    """Compute contrast ratio for two colors
        
    https://www.w3.org/TR/WCAG21/#dfn-contrast-ratio

    Args:
        color1: tuple of color that wait for compare
        color2: tuple of color that wait for compare

    Returns:
        computed contrast ratio value defined by WCAG in range [1 ~ 21]
    """
    L1 = relative_luminance(*color1)
    L2 = relative_luminance(*color2)
    if L1 < L2:
        L1, L2 = L2, L1
    return (L1 + 0.05) / (L2 + 0.05)

assert( contrast_ratio((0, 0, 0), (0, 0, 0)) == 1 )         # shown as 1:1
assert( contrast_ratio((0, 0, 0), (255, 255, 255)) == 21 )  # shown as 21:1