package clock

import (
	"sync"
	"time"
)

// FakeClock is a controllable Clock for tests. Construct with NewFake; advance
// time with Advance; jump to a specific time with Set. Safe for concurrent use.
type FakeClock struct {
	mu  sync.Mutex
	now time.Time
}

// NewFake returns a FakeClock initialized to t.
func NewFake(t time.Time) *FakeClock {
	return &FakeClock{now: t}
}

func (c *FakeClock) Now() time.Time {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.now
}

// Advance moves the clock forward by d.
func (c *FakeClock) Advance(d time.Duration) {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.now = c.now.Add(d)
}

// Set jumps the clock to t.
func (c *FakeClock) Set(t time.Time) {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.now = t
}