A Kotlin script to normalize hex colour representations ("#RGB", "#ARGB", "#RRGGBB", "#AARRGGBB") into "#AARRGGBB", useful for when you're trying to find all unique colours in your app

normalizeColorHex.kts

/*
 * ----------------------------------------------------------------------------
 * "THE BEER-WARE LICENSE" (Revision 42):
 * Sebastiano Poggi wrote this file.  As long as you retain this notice you
 * can do whatever you want with this stuff. If we meet some day, and you think
 * this stuff is worth it, you can buy me a beer in return.   Seb
 * ----------------------------------------------------------------------------
 * Feel free to attribute this code in compiled products if you feel like it,
 * but it's not required.
 */

import java.util.Locale
import kotlin.text.toRegex

private val colorHexRegex = "#?([0-9a-f]{3,8})".toRegex(RegexOption.IGNORE_CASE)

fun normalizeColorHex(colorHex: String): String {
    val matchResult = colorHexRegex.matchEntire(colorHex)
        ?: throw IllegalArgumentException("The provided colorHex '$colorHex' is not a valid color hex")

    val hexValue = matchResult.groups[1]!!.value.toLowerCase(Locale.US)
    val normalizedArgb = when (hexValue.length) {
        3 -> expandToTwoDigitsPerComponent("f$hexValue")
        4 -> expandToTwoDigitsPerComponent(hexValue)
        6 -> "ff$hexValue"
        8 -> hexValue
        else -> throw IllegalArgumentException("The provided colorHex '$colorHex' is not in a supported format")
    }
    
    return "#$normalizedArgb"
}

fun expandToTwoDigitsPerComponent(hexValue: String) =
    hexValue.asSequence()
        .map { "$it$it" }
        .reduce { accumulatedHex, component -> accumulatedHex + component }