// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package fxtime

import (
	"time"
)

// Clock tells the current time.  Time is always given in UTC.
type Clock interface {
	Now() time.Time
}

func NewClock() Clock {
	return clock{}
}

// NewFixedClock returns a clock that always tells the same time. This is useful for
// testing.
func NewFixedClock(moment time.Time) Clock {
	return fixedClock{moment: moment}
}

// Stopwatch measures time intervals.
type Stopwatch interface {
	Restart() time.Time
	Elapsed() time.Duration
}

// NewStopwatch returns a new stopwatch. The watch's initial time is set to clock.Now()
func NewStopwatch(clock Clock) Stopwatch {
	sw := &stopwatch{clock: clock}
	sw.Restart()
	return sw
}

type stopwatch struct {
	clock Clock
	start time.Time
}

func (s *stopwatch) Restart() time.Time {
	s.start = s.clock.Now()
	return s.start
}

func (s stopwatch) Elapsed() time.Duration {
	return s.clock.Now().Sub(s.start)
}

type clock struct{}

func (c clock) Now() time.Time {
	return time.Now().UTC()
}

type fixedClock struct {
	moment time.Time
}

func (c fixedClock) Now() time.Time {
	return c.moment.UTC()
}