Normalize Color String

NormalizeColor.kt

private fun normalizeColor(colorString: String?): String? {
    if (colorString.isNullOrEmpty()) {
        return null
    }
    if (isInvalidColor(colorString)) {
        return null
    }
    return if (isValidColorByLength(colorString)) {
        colorString
    } else {
        val start = colorString.length.minus(6)
        val normalizedColor = colorString.substring(start)
        "#$normalizedColor"
    }
}

private fun isInvalidColor(
    colorString: String
): Boolean {
    val minimumValidColorLengthWithHash = 7
    val maximumValidColorLengthWithHash = 9
    val colorStringLength = colorString.length
    return !colorString.startsWith("#") ||
            colorStringLength < minimumValidColorLengthWithHash ||
            colorStringLength > maximumValidColorLengthWithHash
}

private fun isValidColorByLength(colorString: String): Boolean {
    val colorStringLength = colorString.length
    return colorStringLength == 7 || colorStringLength ==9
}

NormalizeColorParameterizedTest.kt

import org.junit.Assert.assertEquals
import org.junit.Test
import org.junit.runner.RunWith
import org.junit.runners.Parameterized
import org.junit.runners.Parameterized.Parameters

@RunWith(Parameterized::class)
class NormalizeColorParameterizedTest(
    private val input: String?,
    private val expected: String?
) {

    @Test
    fun shouldReturnExpectedColorCodeForColorString() {
        val result = normalizeColor(input)
        assertEquals(expected, result)
    }

    companion object {
        @JvmStatic
        @Parameters(name = "{index}: Input: {0} -> Output: {1}")
        fun data(): List<Array<out String?>> = listOf(
            arrayOf(null, null),
            arrayOf("", null),
            arrayOf("AABBCC", null),
            arrayOf("#FFFFF", null),
            arrayOf("#EEAABBCCD", null),
            arrayOf("#AABBCC", "#AABBCC"),
            arrayOf("#EEAABBCC", "#EEAABBCC"),
            arrayOf("#AFF0097", "#FF0097")
        )
    }

    private fun normalizeColor(colorString: String?): String? {
        if (colorString.isNullOrEmpty()) {
            return null
        }

        if (isInvalidColor(colorString)) {
            return null
        }

        return if (isValidColorByLength(colorString)) {
            colorString
        } else {
            val start = colorString.length.minus(6)
            val normalizedColor = colorString.substring(start)
            "#$normalizedColor"
        }
    }

    private fun isInvalidColor(
        colorString: String
    ): Boolean {
        val minimumValidColorLengthWithHash = 7
        val maximumValidColorLengthWithHash = 9
        val colorStringLength = colorString.length
        return !colorString.startsWith("#") ||
                colorStringLength < minimumValidColorLengthWithHash ||
                colorStringLength > maximumValidColorLengthWithHash
    }

    private fun isValidColorByLength(colorString: String): Boolean {
        val colorStringLength = colorString.length
        return colorStringLength == 7 || colorStringLength == 9
    }
}