export const BLACK = 0;
export const WHITE = 255;

function validHex(color: string): string {

    /* validate color is a hex color */
    color = color.replace(/[^0-9a-f]/gi, '');
    if (color.length === 3)
        color = color[0] + color[0] + color[1] + color[1] + color[2] + color[2];
    if (color.length === 8)
        color = color.substring(0, 6);
    if (color.length !== 6) throw new Error(color + " is not a valid hex color");

    /* return the first 6 hex digits */
    return color;
    
};

/**
 * Convert a color to a ligher shade.
 * @param color the original color as a hex string (e.g. #fff or ABCDEF)
 * @param luminosity the fraction by which to change the brightness, from 0 to 1
 */
export function lighten(color: string, luminosity: number) {

    /* validate color is a hex color */
    color = validHex(color);

    /* calculate lighter color and return */
    let newColor: string = '#';
    for (let i = 0; i < 3; ++i) {
        const c = parseInt(color.substr(i * 2, 2), 16);
        const s = Math.round(Math.min(Math.max(BLACK, c + luminosity * WHITE), WHITE)).toString(16);
        newColor += ('00' + s).substr(s.length);
    }
    return newColor;
    
};

/**
 * Validates a hex color and parses it to an integer.
 * @param color the color as a hex string (e.g. #fff or ABCDEF)
 */
export function parseHex(color: string): number {
    return parseInt(validHex(color), 16)
};

export function zeroPadHex(h: number): string {
    if (h >= 16) return h.toString(16);
    return `0${h.toString(16)}`;
}