package com.lemenzo.calculator.engine

import java.math.BigDecimal

object NumberInputParser {
    fun parse(raw: String, decimalSeparator: Char, groupingSeparator: Char): BigDecimal? {
        var value = raw.trim()
            .replace("\u00A0", "")
            .replace("\u202F", "")
            .replace(" ", "")
        if (value.isEmpty()) return null

        if (decimalSeparator == groupingSeparator) {
            return value.replace(decimalSeparator, '.').toBigDecimalOrNull()
        }

        if (value.contains(decimalSeparator)) {
            value = value.replace(groupingSeparator.toString(), "")
            value = value.replace(decimalSeparator, '.')
            return value.toBigDecimalOrNull()
        }

        if (value.contains(groupingSeparator)) {
            val count = value.count { it == groupingSeparator }
            if (count == 1) {
                val index = value.indexOf(groupingSeparator)
                val digitsAfter = value.length - index - 1
                // Exactly three trailing digits is most likely locale grouping
                // (1,000 / 1.000). Other single-separator forms are accepted
                // as pasted decimal notation (1,5 / 1.5 / 1,25 / 1.2345).
                value = if (digitsAfter == 3 && value.substring(index + 1).all(Char::isDigit)) {
                    value.removeRange(index, index + 1)
                } else {
                    value.replace(groupingSeparator, '.')
                }
            } else {
                value = value.replace(groupingSeparator.toString(), "")
            }
        }
        return value.toBigDecimalOrNull()
    }
}