package slotutil

import (
	"time"

	types "github.com/prysmaticlabs/eth2-types"
	"github.com/prysmaticlabs/prysm/shared/params"
	"github.com/prysmaticlabs/prysm/shared/timeutils"
)

// SlotStartTime returns the start time in terms of its unix epoch
// value.
func SlotStartTime(genesis uint64, slot types.Slot) time.Time {
	duration := time.Second * time.Duration(slot.Mul(params.BeaconConfig().SecondsPerSlot))
	startTime := time.Unix(int64(genesis), 0).Add(duration)
	return startTime
}

// SlotsSinceGenesis returns the number of slots since
// the provided genesis time.
func SlotsSinceGenesis(genesis time.Time) types.Slot {
	if genesis.After(timeutils.Now()) { // Genesis has not occurred yet.
		return 0
	}
	return types.Slot(uint64(timeutils.Since(genesis).Seconds()) / params.BeaconConfig().SecondsPerSlot)
}

// EpochsSinceGenesis returns the number of slots since
// the provided genesis time.
func EpochsSinceGenesis(genesis time.Time) types.Epoch {
	return types.Epoch(SlotsSinceGenesis(genesis) / params.BeaconConfig().SlotsPerEpoch)
}

// DivideSlotBy divides the SECONDS_PER_SLOT configuration
// parameter by a specified number. It returns a value of time.Duration
// in milliseconds, useful for dividing values such as 1 second into
// millisecond-based durations.
func DivideSlotBy(timesPerSlot int64) time.Duration {
	return time.Duration(int64(params.BeaconConfig().SecondsPerSlot*1000)/timesPerSlot) * time.Millisecond
}

// MultiplySlotBy multiplies the SECONDS_PER_SLOT configuration
// parameter by a specified number. It returns a value of time.Duration
// in millisecond-based durations.
func MultiplySlotBy(times int64) time.Duration {
	return time.Duration(int64(params.BeaconConfig().SecondsPerSlot)*times) * time.Second
}

// AbsoluteValueSlotDifference between two slots.
func AbsoluteValueSlotDifference(x, y types.Slot) uint64 {
	if x > y {
		return uint64(x.SubSlot(y))
	}
	return uint64(y.SubSlot(x))
}