// Copyright 2009 The Go 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 time

import "errors"

// A Ticker holds a synchronous channel that delivers `ticks' of a clock
// at intervals.
type Ticker struct {
	C <-chan int64 // The channel on which the ticks are delivered.
	r runtimeTimer
}

// NewTicker returns a new Ticker containing a channel that will
// send the time, in nanoseconds, every ns nanoseconds.  It adjusts the
// intervals to make up for pauses in delivery of the ticks. The value of
// ns must be greater than zero; if not, NewTicker will panic.
func NewTicker(ns int64) *Ticker {
	if ns <= 0 {
		panic(errors.New("non-positive interval for NewTicker"))
	}
	// Give the channel a 1-element time buffer.
	// If the client falls behind while reading, we drop ticks
	// on the floor until the client catches up.
	c := make(chan int64, 1)
	t := &Ticker{
		C: c,
		r: runtimeTimer{
			when:   Nanoseconds() + ns,
			period: ns,
			f:      sendTime,
			arg:    c,
		},
	}
	startTimer(&t.r)
	return t
}

// Stop turns off a ticker.  After Stop, no more ticks will be sent.
func (t *Ticker) Stop() {
	stopTimer(&t.r)
}

// Tick is a convenience wrapper for NewTicker providing access to the ticking
// channel only.  Useful for clients that have no need to shut down the ticker.
func Tick(ns int64) <-chan int64 {
	if ns <= 0 {
		return nil
	}
	return NewTicker(ns).C
}