Android TextView formatted to show Currency values from a Float

PriceTextView.kt

package com.example

import android.content.Context
import android.support.v7.widget.AppCompatTextView
import android.util.AttributeSet
import java.text.DecimalFormat
import java.util.Currency

class PriceTextView(context: Context, attrs: AttributeSet?) : AppCompatTextView(context, attrs) {

    companion object {
        private const val DEFAULT_PRICE = "0"
    }

    private val currencyFormatter = DecimalFormat.getCurrencyInstance() as DecimalFormat
    private var maximumIntegerDigits = currencyFormatter.maximumIntegerDigits
    private var maximumFractionDigits = currencyFormatter.maximumFractionDigits
    private var decimalSeparator = currencyFormatter.decimalFormatSymbols.decimalSeparator

    private var valueListener: ((Double) -> Unit)? = null
    private var errorListener: (() -> Unit)? = null
    private var currentPrice = DEFAULT_PRICE

    override fun onFinishInflate() {
        super.onFinishInflate()
        updatePrice()
    }

    fun addNumber(number: Int) {
        if (currentPrice != DEFAULT_PRICE) {
            val parts = currentPrice.toRationalNumber()
            if (parts.second != null) {
                if (parts.second!!.length < maximumFractionDigits) {
                    currentPrice += number
                } else {
                    errorListener?.invoke()
                }
            } else {
                if (parts.first.length < maximumIntegerDigits) {
                    currentPrice += number
                } else {
                    errorListener?.invoke()
                }
            }
        } else {
            currentPrice = number.toString()
        }
        updatePrice()
    }

    fun addDecimalSeparator() {
        if (maximumFractionDigits > 0 && !currentPrice.contains(decimalSeparator)) {
            currentPrice += decimalSeparator
            updatePrice()
        }
    }

    fun removeLastNumber() {
        if (currentPrice != DEFAULT_PRICE) {
            currentPrice =
                if (currentPrice.length > 1) {
                    if (currentPrice.last() == decimalSeparator) {
                        if (currentPrice.length > 2) {
                            currentPrice.dropLast(2)
                        } else {
                            DEFAULT_PRICE
                        }
                    } else {
                        currentPrice.dropLast(1)
                    }
                } else {
                    DEFAULT_PRICE
                }
        }
        updatePrice()
    }

    fun setPrice(value: Double?) {
        if (value == null) {
            resetPrice()
        } else if (value != currentPrice.toDoubleOrNull()) {
            currentPrice = value.toString()
            updatePrice()
        }
    }

    fun getPrice(): Double =
        currentPrice.toDouble()

    fun resetPrice() {
        currentPrice = DEFAULT_PRICE
        updatePrice()
    }

    fun setCurrency(currency: Currency) {
        currencyFormatter.currency = currency
        maximumIntegerDigits = currencyFormatter.maximumIntegerDigits
        maximumFractionDigits = currencyFormatter.maximumFractionDigits
        decimalSeparator = currencyFormatter.decimalFormatSymbols.decimalSeparator
        updatePrice()
    }

    fun setValueListener(listener: (Double) -> Unit) {
        this.valueListener = listener
    }

    fun setErrorListener(listener: () -> Unit) {
        this.errorListener = listener
    }

    private fun updatePrice() {
        if (currentPrice.isBlank()) currentPrice = DEFAULT_PRICE

        val priceDouble = currentPrice.toDouble()
        text = currencyFormatter.format(priceDouble)
        valueListener?.invoke(priceDouble)
    }

    private fun String.toRationalNumber(): Pair<String, String?> {
        val split = trim().split(decimalSeparator)
        val integer = split.first()
        val decimal = split.getOrNull(1)
        return Pair(integer, decimal)
    }
}