/* Gets percieved luminance of a color */
function getLuminance(color: string): number {
    const {r, g, b} = hexToRgb(color);
    return Math.sqrt(0.299 * (r * r) + 0.587 * (g * g) + 0.114 * (b * b));
}

/* From https://stackoverflow.com/a/5624139 */
function hexToRgb(hex: string): {r: number; g: number; b: number} {
    // Expand shorthand form (e.g. "03F") to full form (e.g. "0033FF")
    const shorthandRegex = /^#?([a-f\d])([a-f\d])([a-f\d])$/i;
    hex = hex.replace(shorthandRegex, function(m, r, g, b) {
      return r + r + g + g + b + b;
    });
  
    const result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex);
    return result ? {
      r: parseInt(result[1], 16),
      g: parseInt(result[2], 16),
      b: parseInt(result[3], 16)
    } : null;
}

/**
 * List of all indexes that have the specified value
 * https://stackoverflow.com/a/54954694/1985387
 */
function indexesOf<T>(array: T[], value: T): number[] {
    return array.map((v, i) => v === value ? i : -1).filter(i => i !== -1);
}

export const GenericUtils = {
    getLuminance,
    indexesOf
}