Formats a double

DoubleFormatter.kt

// If you are using this, please upvote this issue: https://youtrack.jetbrains.com/issue/KT-21644

fun Double.toString(
    minDecimals: Int,
    maxDecimals: Int = minDecimals,
    minIntegrals: Int = 1,
    addPositiveSign: Boolean = false,
): String {
    require(minDecimals <= maxDecimals) { "minDecimals > maxDecimals" }
    require(minDecimals >= 0) { "minDecimals < 0" }
    require(minIntegrals >= 1) { "minIntegrals < 1" }

    val sign = if (this < 0) -1 else 1
    val number = this * sign

    val (_, fullDecStr) = number.toString().split('.')
    var int = number.toInt()

    var decStr = fullDecStr
    if (decStr.length > maxDecimals) {
        decStr = fullDecStr.substring(0, maxDecimals)
    }

    if (fullDecStr.length > maxDecimals && fullDecStr[maxDecimals] in '5'..'9') {
        // Need rounding
        val digits = decStr.toCharArray()
        var index = maxDecimals -1
        var needRound = true
        while (index >= 0 && needRound) {
            digits[index] = ((digits[index].toString().toInt() + 1) % 10).toString()[0]
            needRound = digits[index] == '0'
            index--
        }
        if (needRound) {
            int += 1
        }
        decStr = digits.concatToString()
    }
    decStr = decStr.trimEnd('0')

    return buildString {
        when {
            sign == -1 -> append('-')
            sign == 1 && addPositiveSign -> append('+')
        }
        append(int.toString().padStart(minIntegrals, '0'))
        if (decStr.isNotEmpty() || minDecimals >= 1) {
            append('.')
            append(decStr.padEnd(minDecimals, '0'))
        }
    }
}