TwoDigitMonthYearInputTextWatcher.kt

import android.annotation.SuppressLint
import android.text.Editable
import android.text.TextWatcher
import android.widget.EditText

private const val INITIAL_MONTH_ADD_ON = "0"
private const val DEFAULT_MONTH = "01"
private const val SEPARATOR = "/"

class TwoDigitMonthYearInputTextWatcher(val editText: EditText) : TextWatcher {
    private var length: Int = 0

    override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {
        // No-op
    }

    override fun beforeTextChanged(s: CharSequence, start: Int, count: Int, after: Int) {
        length = editText.text.length
    }

    @SuppressLint("SetTextI18n")
    override fun afterTextChanged(s: Editable) {
        val currentLength = editText.text.length

        // We do nothing if the user is deleting
        if (length > currentLength) {
            return
        }

        if ((s.length == 1 && !s[0].isDigit())
            || (s.length == 2 && s[0].toString() == INITIAL_MONTH_ADD_ON && s[s.length - 1].toString() == SEPARATOR)
        ) {
            editText.setText(DEFAULT_MONTH + SEPARATOR)
        } else if (s.length == 1 && s[0].isBiggerThan(1)) {
            editText.setText(INITIAL_MONTH_ADD_ON + s[0].toString() + SEPARATOR)
        } else if (s.length == 2 && s[s.length - 1].toString() == SEPARATOR) {
            editText.setText(INITIAL_MONTH_ADD_ON + s.toString())
        } else if (s.length == 2 && s[s.length - 1].isBiggerThan(2)) {
            var month = INITIAL_MONTH_ADD_ON + s[0].toString()
            if (s[0].toString() == INITIAL_MONTH_ADD_ON) {
                month = DEFAULT_MONTH
            }
            editText.setText(month + SEPARATOR + s[1].toString())
        } else if (s.length == 2 && s[s.length - 1].toString() != SEPARATOR) {
            editText.setText(editText.text.toString() + SEPARATOR)
        } else if (s.length == 3 && s[s.length - 1].toString() != SEPARATOR) {
            s.insert(2, SEPARATOR)
            editText.setText(s.toString())
        } else if (s.length > 3 && s[0].isBiggerThan(1)) {
            editText.setText(INITIAL_MONTH_ADD_ON + s)
        }

        editText.setSelection(editText.text.toString().length)
    }

    private fun Char.isBiggerThan(num: Int): Boolean {
        return this.isDigit() && this.toString().toInt() > num
    }

}