yaotp/app/src/main/java/com/chameth/yaotp/algos/Totp.kt

package com.chameth.yaotp.algos

import java.nio.ByteBuffer

data class TotpParams(val hotpParams: HotpParams, val startTime: Long = 0, val step: Int = 30)

fun totp(totpParams: TotpParams, currentTime: Long = currentTime()): Otp {
    val hotp = hotp(totpParams.hotpParams, count(totpParams.startTime, totpParams.step, currentTime).toByteArray())
    return Otp(hotp.otp, expiry(totpParams.startTime, totpParams.step, currentTime))
}

internal fun count(startTime: Long, step: Int, currentTime: Long) = (currentTime - startTime) / step

internal fun currentTime() = System.currentTimeMillis() / 1000

internal fun Long.toByteArray() = ByteBuffer.allocate(java.lang.Long.BYTES).putLong(this).array()

internal fun expiry(startTime: Long, step: Int, currentTime: Long) = currentTime + step - (currentTime - startTime) % step