package com.infendro.otp

import com.infendro.hash.HashFunction
import com.infendro.hash.sha1.SHA1
import kotlin.time.Duration
import kotlin.time.Duration.Companion.seconds
import kotlin.time.Instant

class TOTP(
    val function: HashFunction = SHA1(),
    val length: Int = 6,
    val period: Duration = 30.seconds,
) {
    private val hotp = HOTP(function, length)

    fun generate(secret: ByteArray, instant: Instant): String {
        return hotp.generate(secret, counter(instant))
    }

    fun verify(secret: ByteArray, instant: Instant, otp: String): Boolean {
        return generate(secret, instant) == otp
    }

    private fun counter(instant: Instant): Long {
        val ms = instant.toEpochMilliseconds()
        val d = period.inWholeMilliseconds
        return ms / d
    }
}