<?php

/**
 * Converts Hex color values into rgba format.
 *
 * @param string $hex
 * @param mixed  $alpha
 * @return string
 */
function hexToRgb($hex, $alpha = 0)
{
    // remove caret symbol from the start
    $hex = ltrim($hex, '#');

    // if short hex codes used, convert them to full length
    if (strlen($hex) === 3) {
        $hex = extendShortHex($hex);
    }

    validateHexColor($hex);

    // chunk hex value by two digits to get r, g and b values
    $hexArray = str_split($hex, 2);

    $hexArray = array_map(function ($item) {
        return hexdec($item);
    }, $hexArray);

    $hexArray['alpha'] = (float)$alpha;

    return "rgb($hexArray[0], $hexArray[1], $hexArray[2], $hexArray[alpha])";
}

/**
 * Validates hex color values by length and the digits.
 *
 * @param string $hex
 * @throws Error
 */
function validateHexColor($hex)
{
    // hex length validation
    if (strlen($hex) !== 6) {
        throw new Error('Hex code must be 6 digits long.');
    }

    // hex digit validation
    if (ctype_xdigit($hex) === false) {
        throw new Error('Please provide a valid hex number.');
    }
}

/**
 * Short hex codes are converted into six digits.
 *
 * @param string $hex
 * @return string
 */
function extendShortHex($hex)
{
    return $hex[0] . $hex[0] . $hex[1] . $hex[1] . $hex[2] . $hex[2];
}