package com.lemenzo.calculator.engine

/**
 * Converts between the locale-neutral expression syntax used by the math engine
 * and the text shown to the user. On locales using comma as the decimal
 * separator, function arguments are displayed with semicolons to avoid the
 * ambiguous `nCr(10,3)` / decimal-comma collision.
 */
object ExpressionCodec {
    fun toDisplay(canonical: String, decimalSeparator: Char): String {
        if (decimalSeparator == '.') return canonical
        return buildString(canonical.length) {
            canonical.forEach { c ->
                append(when (c) {
                    '.' -> decimalSeparator
                    ',' -> ';'
                    else -> c
                })
            }
        }
    }

    fun toCanonical(display: String, decimalSeparator: Char): String {
        return buildString(display.length) {
            display.forEach { c ->
                append(when {
                    c == decimalSeparator -> '.'
                    decimalSeparator != '.' && c == ';' -> ','
                    c == '×' -> '*'
                    c == '÷' -> '/'
                    c == '−' -> '-'
                    else -> c
                })
            }
        }
    }
}