MoneyTextWatcher.kt

import android.text.Editable
import android.text.TextWatcher
import android.text.method.DigitsKeyListener
import android.widget.EditText
import java.lang.ref.WeakReference
import java.math.BigDecimal
import java.text.NumberFormat
import java.util.*

class MoneyTextWatcher(editText: EditText, locale: Locale, val maxLength: Int = 14, val maxFractionDigits: Int = 0) : TextWatcher {
    private val editTextWeakReference = WeakReference<EditText>(editText)

    val punctuationRegex = "[,.]".toRegex()
    val letterRegex = "[^\\d.]".toRegex()

    val currency: String = Currency.getInstance(locale).symbol
    val numberFormatter: NumberFormat = NumberFormat.getNumberInstance(locale)
            .also {
                it.maximumFractionDigits = maxFractionDigits
            }
    init {
        editText.keyListener = DigitsKeyListener.getInstance("0123456789 $currency")
    }

    override fun beforeTextChanged(s: CharSequence, start: Int, count: Int, after: Int) {}

    override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {}

    override fun afterTextChanged(editable: Editable) {
        val editText = editTextWeakReference.get() ?: return
        val cleanString = editable.toString().replace(currency, "").replace(letterRegex, "").replace(punctuationRegex, "").trim()
        val parsed = if (cleanString.isNullOrEmpty()) null else BigDecimal(cleanString)
                .apply {
                    if (maxFractionDigits > 0) {
                        setScale(2, BigDecimal.ROUND_FLOOR)
                        divide(BigDecimal(100), BigDecimal.ROUND_FLOOR)
                    }
                }

        val formatted = parsed?.let { "$currency ${numberFormatter.format(it)}".let { it.substring(0, minOf(maxLength - 1, it.length)) } } ?: ""

        with (editText) {
            removeTextChangedListener(this@MoneyTextWatcher)
            editable.replace(0, editable.length, formatted)
            addTextChangedListener(this@MoneyTextWatcher)
        }
    }
}