package xcanvas

import "sort"
import "math"
import "image"
import "github.com/jezek/xgbutil/xgraphics"

func (this *pen) textureRectangle (bounds image.Rectangle) {
	if this.texture.Opaque() {
		this.textureRectangleOpaque(bounds)
	} else {
		this.textureRectangleTransparent(bounds)
	}
}

func (this *pen) textureRectangleOpaque (bounds image.Rectangle) {
	dstBounds := bounds.Intersect(this.image.Bounds())
	var pos image.Point

	dst := this.image.Pix
	src := this.texture.pix
	offset := this.texture.rect.Min.Sub(bounds.Min)

	for pos.Y = dstBounds.Min.Y; pos.Y < dstBounds.Max.Y; pos.Y ++ {
	for pos.X = dstBounds.Min.X; pos.X < dstBounds.Max.X; pos.X ++ {
		srcPos := pos.Add(offset)
		dstIndex := this.image.PixOffset(pos.X, pos.Y)
		srcIndex := this.texture.PixOffset(srcPos.X, srcPos.Y)
		dst[dstIndex + 0] = src[srcIndex + 0]
		dst[dstIndex + 1] = src[srcIndex + 1]
		dst[dstIndex + 2] = src[srcIndex + 2]
		dst[dstIndex + 3] = src[srcIndex + 3]
	}}
}

func (this *pen) textureRectangleTransparent (bounds image.Rectangle) {
	dstBounds := bounds.Intersect(this.image.Bounds())
	var pos image.Point

	dst := this.image.Pix
	src := this.texture.pix
	offset := this.texture.rect.Min.Sub(bounds.Min)

	for pos.Y = dstBounds.Min.Y; pos.Y < dstBounds.Max.Y; pos.Y ++ {
	for pos.X = dstBounds.Min.X; pos.X < dstBounds.Max.X; pos.X ++ {
		srcPos := pos.Add(offset)
		dstIndex := this.image.PixOffset(pos.X, pos.Y)
		srcIndex := this.texture.PixOffset(srcPos.X, srcPos.Y)
		pixel := xgraphics.BlendBGRA(xgraphics.BGRA {
			B: dst[dstIndex + 0],
			G: dst[dstIndex + 1],
			R: dst[dstIndex + 2],
			A: dst[dstIndex + 3],
		}, xgraphics.BGRA {
			B: src[srcIndex + 0],
			G: src[srcIndex + 1],
			R: src[srcIndex + 2],
			A: src[srcIndex + 3],
		})
		dst[dstIndex + 0] = pixel.B
		dst[dstIndex + 1] = pixel.G
		dst[dstIndex + 2] = pixel.R
		dst[dstIndex + 3] = pixel.A
	}}
}

func (this *pen) fillRectangle (c xgraphics.BGRA, bounds image.Rectangle) {
	if c.A == 255 {
		this.fillRectangleOpaque(c, bounds)
	} else {
		this.fillRectangleTransparent(c, bounds)
	}
}

func (this *pen) fillRectangleOpaque (c xgraphics.BGRA, bounds image.Rectangle) {
	bounds = bounds.Intersect(this.image.Bounds())
	var pos image.Point

	for pos.Y = bounds.Min.Y; pos.Y < bounds.Max.Y; pos.Y ++ {
	for pos.X = bounds.Min.X; pos.X < bounds.Max.X; pos.X ++ {
		index := this.image.PixOffset(pos.X, pos.Y)
		this.image.Pix[index + 0] = c.B
		this.image.Pix[index + 1] = c.G
		this.image.Pix[index + 2] = c.R
		this.image.Pix[index + 3] = c.A
	}}
}

func (this *pen) fillRectangleTransparent (c xgraphics.BGRA, bounds image.Rectangle) {
	bounds = bounds.Intersect(this.image.Bounds())
	var pos image.Point

	for pos.Y = bounds.Min.Y; pos.Y < bounds.Max.Y; pos.Y ++ {
	for pos.X = bounds.Min.X; pos.X < bounds.Max.X; pos.X ++ {
		index := this.image.PixOffset(pos.X, pos.Y)
		pixel := xgraphics.BlendBGRA(xgraphics.BGRA {
			B: this.image.Pix[index + 0],
			G: this.image.Pix[index + 1],
			R: this.image.Pix[index + 2],
			A: this.image.Pix[index + 3],
		}, c)
		this.image.Pix[index + 0] = pixel.B
		this.image.Pix[index + 1] = pixel.G
		this.image.Pix[index + 2] = pixel.R
		this.image.Pix[index + 3] = pixel.A
	}}
}

func (this *pen) strokeRectangle (c xgraphics.BGRA, bounds image.Rectangle) {
	if this.weight > bounds.Dx() / 2 || this.weight > bounds.Dy() / 2 {
		this.fillRectangle(c, bounds)
		return
	}

	top := image.Rect (
		bounds.Min.X,
		bounds.Min.Y,
		bounds.Max.X,
		bounds.Min.Y + this.weight)
	bottom := image.Rect (
		bounds.Min.X,
		bounds.Max.Y - this.weight,
		bounds.Max.X,
		bounds.Max.Y)
	left := image.Rect (
		bounds.Min.X,
		bounds.Min.Y + this.weight,
		bounds.Min.X + this.weight,
		bounds.Max.Y - this.weight)
	right := image.Rect (
		bounds.Max.X - this.weight,
		bounds.Min.Y + this.weight,
		bounds.Max.X,
		bounds.Max.Y - this.weight)

	this.fillRectangle(c, top,)
	this.fillRectangle(c, bottom,)
	this.fillRectangle(c, left,)
	this.fillRectangle(c, right,)
}

// the polygon filling algorithm is adapted from:
// https://www.alienryderflex.com/polygon_fill/
// (if you write C like that i will disassemble you)

func (this *pen) fillPolygon (c xgraphics.BGRA, points ...image.Point) {
	if len(points) < 3 { return }

	// figure out the bounds of the polygon so we don't test empty space
	var area image.Rectangle
	area.Min = points[0]
	area.Max = points[0]
	for _, point := range points[1:] {
		if point.X < area.Min.X { area.Min.X = point.X }
		if point.Y < area.Min.Y { area.Min.Y = point.Y }
		if point.X > area.Max.X { area.Max.X = point.X }
		if point.Y > area.Max.Y { area.Max.Y = point.Y }
	}
	area = this.image.Bounds().Intersect(area)
	if area.Empty() { return }

	boundaries := make([]int, len(points))
	context := fillingContext {
		image:      this.image,
		color:      this.fill,
		min:        area.Min.X,
		max:        area.Max.X,
		points:     points,
	}

	for context.y = area.Min.Y; context.y < area.Max.Y; context.y ++ {
		// build boundary list
		boundaryCount := 0
		prevPoint := points[len(points) - 1]
		for _, point := range points {
			fy      := float64(context.y)
			fPointX := float64(point.X)
			fPointY := float64(point.Y)
			fPrevX  := float64(prevPoint.X)
			fPrevY  := float64(prevPoint.Y)
			addboundary :=
				(fPointY < fy && fPrevY  >= fy) ||
				(fPrevY  < fy && fPointY >= fy)
			if addboundary {
				boundaries[boundaryCount] = int(math.Round (
					fPointX +
					(fy - fPointY) /
					(fPrevY - fPointY) *
					(fPrevX - fPointX)))
				boundaryCount ++
			}
			prevPoint = point
		}

		// sort boundary list
		context.boundaries = boundaries[:boundaryCount]
		sort.Ints(context.boundaries)

		// fill pixels between boundary pairs
		if c.A == 255 {
			context.fillPolygonHotOpaque()
		} else {
			context.fillPolygonHotTransparent()
		}
	}

}

type fillingContext struct {
	image      *xgraphics.Image
	color      xgraphics.BGRA
	min, max   int
	y          int
	boundaries []int
	points     []image.Point
}

func (context *fillingContext) fillPolygonHotOpaque () {
	for index := 0; index < len(context.boundaries) - 1; index += 2 {
		left  := context.boundaries[index]
		right := context.boundaries[index + 1]

		// stop if we have exited the polygon
		if left >= context.max { break }
		// begin filling if we are within the polygon
		if right > context.min {
			// constrain boundaries to image size
			if left  < context.min { left  = context.min }
			if right > context.max { right = context.max }

			// fill pixels in between
			for x := left; x < right; x ++ {
				index := context.image.PixOffset(x, context.y)
				context.image.Pix[index + 0] = context.color.B
				context.image.Pix[index + 1] = context.color.G
				context.image.Pix[index + 2] = context.color.R
				context.image.Pix[index + 3] = context.color.A
			}
		}
	}
}

func (context *fillingContext) fillPolygonHotTransparent () {
	for index := 0; index < len(context.boundaries) - 1; index += 2 {
		left  := context.boundaries[index]
		right := context.boundaries[index + 1]

		// stop if we have exited the polygon
		if left >= context.max { break }
		// begin filling if we are within the polygon
		if right > context.min {
			// constrain boundaries to image size
			if left  < context.min { left  = context.min }
			if right > context.max { right = context.max }

			// fill pixels in between
			for x := left; x < right; x ++ {
				index := context.image.PixOffset(x, context.y)
				pixel := xgraphics.BlendBGRA(xgraphics.BGRA {
					B: context.image.Pix[index + 0],
					G: context.image.Pix[index + 1],
					R: context.image.Pix[index + 2],
					A: context.image.Pix[index + 3],
				}, context.color)
				context.image.Pix[index + 0] = pixel.B
				context.image.Pix[index + 1] = pixel.G
				context.image.Pix[index + 2] = pixel.R
				context.image.Pix[index + 3] = pixel.A
			}
		}
	}
}

func (this *pen) strokePolygon (c xgraphics.BGRA, points ...image.Point) {
	prevPoint := points[len(points) - 1]
	for _, point := range points {
		this.line(c, prevPoint, point)
		prevPoint = point
	}
}

func (this *pen) polyLine (c xgraphics.BGRA, points ...image.Point) {
	if len(points) < 2 { return }
	prevPoint := points[0]
	for _, point := range points[1:] {
		this.line(c, prevPoint, point)
		prevPoint = point
	}
}

func wrap (n, min, max int) int {
	max -= min
	n   -= min
	n   %= max
	if n < 0 { n += max }
	return n + min
}