package fastqueue

import "runtime"

const (
	SpinMask = 1024*16 - 1 // arbitrary; we'll want to experiment with different values
)

type DefaultWriter struct {
	written  *Cursor // the ring buffer has been written up to this sequence
	upstream Barrier // all of the readers have advanced up to this sequence
	capacity int64
	previous int64
	gate     int64
}

func NewWriter(written *Cursor, upstream Barrier, capacity int64) *DefaultWriter {
	return &DefaultWriter{
		upstream: upstream,
		written:  written,
		capacity: capacity,
		previous: defaultCursorValue,
		gate:     defaultCursorValue,
	}
}

func (this *DefaultWriter) Reserve(count int64) int64 {
	if count <= 0 {
		panic(ErrMinimumReservationSize)
	}

	this.previous += count
	for spin := int64(0); this.previous-this.capacity > this.gate; spin++ {
		if spin&SpinMask == 0 {
			runtime.Gosched() // LockSupport.parkNanos(1L); http://bit.ly/1xiDINZ
		}

		this.gate = this.upstream.Load()
	}
	return this.previous
}

func (this *DefaultWriter) Commit(_, upper int64) {
	this.written.Store(upper)
}