// Package times provides a clock interface with implementations for production and testing code.
package times

import "time"

// Clock defines an interface with primitives for time related functionality.
type Clock interface {

	// Now returns the current time.
	Now() time.Time

	// After returns a channel that can be used to receive the current time once, after the specified
	// duration has passed.
	After(time.Duration) <-chan time.Time
}

// TestClock is a test implementation of the Clock interface. On top of the Clock methods, it adds the
// possibility to manually step time or to virtually jump to a specified time.
type TestClock struct{
	clock test
}

// Sys returns the Clock implementation based on the standard library time functions. Meant to be used with
// production code.
func Sys() Clock {
	return sys{}
}

// Test creates a Clock implementation with manual time stepping function. Meant to be used with testing code.
func Test() TestClock {
	var zero time.Time
	return TestFrom(zero)
}

// TestFrom creates a Clock implementation with manual time stepping function, starting from the specified time.
// Meant to be used with testing code.
func TestFrom(t time.Time) TestClock {
	return TestClock{clock: makeTestClock(t)}
}

// Now returns the current test time.
func (c TestClock) Now() time.Time {
	return c.clock.now()
}

// After returns a channel that communicates the current time if the specified duration has passed.
func (c TestClock) After(d time.Duration) <-chan time.Time {
	return c.clock.after(d)
}

// Pass turns the clock forward by d duration. Negative d is considered as 0.
func (c TestClock) Pass(d time.Duration) {
	c.clock.pass(d)
}

// Jump sets the clock to time specified by t. Values of t in the past, relative to TestClock's current time,
// are ignored.
func (c TestClock) Jump(t time.Time) {
	c.clock.jump(t)
}