package function.builtin.predicate

import function.ArgumentValidator
import function.FunctionNames
import function.LispFunction
import sexpression.Cons
import sexpression.LispNumber
import sexpression.Nil
import sexpression.SExpression
import sexpression.Symbol.Companion.T

@FunctionNames("=")
class NumericEqual(name: String) : LispFunction() {

    private val argumentValidator = ArgumentValidator(name).apply {
        setMinimumNumberOfArguments(1)
        setEveryArgumentExpectedType(LispNumber::class.java)
    }

    override fun call(argumentList: Cons): SExpression {
        argumentValidator.validate(argumentList)

        return callTailRecursive(argumentList)
    }

    private tailrec fun callTailRecursive(argumentList: Cons): SExpression {
        val remainingArguments = argumentList.rest as Cons

        if (remainingArguments.isNull)
            return T

        val number1 = argumentList.first as LispNumber
        val number2 = remainingArguments.first as LispNumber

        return if (number1.value != number2.value) Nil else callTailRecursive(remainingArguments)
    }
}