time.go

package common

import (
	"math"
	"time"
)

// time.Unix will add `time.unixToInternal` to a unix timestamp in int64 space.
// TimeOfRound will stay below this buffer so that such a conversion does not overflow.
const timeBufferBits = 36
const maxTimeBuffer = int64(1 << timeBufferBits)

// TimeOfRoundErrorValue is the value returned by `TimeOfRound` when an invalid round is
// specified.
const TimeOfRoundErrorValue = math.MaxInt64 - maxTimeBuffer

// TimeOfRound is returning the time the current round should happen
func TimeOfRound(period time.Duration, genesis int64, round uint64) int64 {
	if round == 0 {
		return genesis
	}
	if period < 0 {
		return TimeOfRoundErrorValue
	}

	periodBits := math.Log2(period.Seconds() + 1)           // require x >=1 in log2(x)
	if round >= (math.MaxUint64 >> (int(periodBits) + 2)) { // +1 for mul overflow, +1 for casting int64
		return TimeOfRoundErrorValue
	}
	// - 1 because genesis time is for 1st round already
	delta := (round - 1) * uint64(period.Seconds())

	val := genesis + int64(delta)
	if val > math.MaxInt64-maxTimeBuffer {
		return TimeOfRoundErrorValue
	}
	return val
}

// CurrentRound calculates the active round at `now`
func CurrentRound(now int64, period time.Duration, genesis int64) uint64 {
	nextRound, _ := NextRound(now, period, genesis)
	if nextRound <= 1 {
		return nextRound
	}
	return nextRound - 1
}

// NextRound returns the next upcoming round and its UNIX time given the genesis
// time and the period.
// round at time genesis = round 1. Round 0 is fixed.
func NextRound(now int64, period time.Duration, genesis int64) (nextRound uint64, nextTime int64) {
	if now < genesis {
		return 1, genesis
	}
	fromGenesis := now - genesis
	// we take the time from genesis divided by the periods in seconds, that
	// gives us the number of periods since genesis. We add +1 since we want the
	// next round. We also add +1 because round 1 starts at genesis time.
	nextRound = uint64(math.Floor(float64(fromGenesis)/period.Seconds())) + 1
	nextTime = genesis + int64(nextRound*uint64(period.Seconds()))
	return nextRound + 1, nextTime
}