package imaging

import (
	"image"
	"runtime"
	"sync"
)

// parallel processes the data in separate goroutines.
func parallel(start, stop int, fn func(<-chan int)) {
	count := stop - start
	if count < 1 {
		return
	}

	procs := runtime.GOMAXPROCS(0)
	if procs > count {
		procs = count
	}

	c := make(chan int, count)
	for i := start; i < stop; i++ {
		c <- i
	}
	close(c)

	var wg sync.WaitGroup
	for i := 0; i < procs; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			fn(c)
		}()
	}
	wg.Wait()
}

// absint returns the absolute value of i.
func absint(i int) int {
	if i < 0 {
		return -i
	}
	return i
}

// clamp rounds and clamps float64 value to fit into uint8.
func clamp(x float64) uint8 {
	v := int64(x + 0.5)
	if v > 255 {
		return 255
	}
	if v > 0 {
		return uint8(v)
	}
	return 0
}

func reverse(pix []uint8) {
	if len(pix) <= 4 {
		return
	}
	i := 0
	j := len(pix) - 4
	for i < j {
		pix[i+0], pix[j+0] = pix[j+0], pix[i+0]
		pix[i+1], pix[j+1] = pix[j+1], pix[i+1]
		pix[i+2], pix[j+2] = pix[j+2], pix[i+2]
		pix[i+3], pix[j+3] = pix[j+3], pix[i+3]
		i += 4
		j -= 4
	}
}

func toNRGBA(img image.Image) *image.NRGBA {
	if img, ok := img.(*image.NRGBA); ok {
		return &image.NRGBA{
			Pix:    img.Pix,
			Stride: img.Stride,
			Rect:   img.Rect.Sub(img.Rect.Min),
		}
	}
	return Clone(img)
}