package clock

import "time"

// Clock is the time source injected into services.
// Production code uses Real(); tests use Fixed().
type Clock interface {
	Now() time.Time
}

// Real returns a Clock backed by time.Now().
func Real() Clock { return realClock{} }

type realClock struct{}

func (realClock) Now() time.Time { return time.Now() }

// FixedClock always returns T. Advance shifts T forward.
// Intended for tests only.
type FixedClock struct{ T time.Time }

// Fixed returns a *FixedClock set to t.
func Fixed(t time.Time) *FixedClock { return &FixedClock{T: t} }

func (f *FixedClock) Now() time.Time { return f.T }

// Advance shifts the clock forward by d.
func (f *FixedClock) Advance(d time.Duration) { f.T = f.T.Add(d) }