// Copyright 2014, 2015 by Sascha L. Teichmann
// Use of this source code is governed by the MIT license
// that can be found in the LICENSE file.

package common

import (
	"image"
	"image/color"
	"math"
)

type Renderer struct {
	width             int
	height            int
	xOfs              int16
	zOfs              int16
	yBuffer           []int32
	yMin              []int32
	cBuffer           []int32
	RejectedBlocks    int
	SolidBlocks       int
	TransparentBlocks int
	spans             *SpanPool
	tBuffer           []*Span
}

func NewRenderer(width, height int, transparent bool) (renderer *Renderer) {
	dim := width * height
	pixSize := dim * 16 * 16
	yBuffer := make([]int32, pixSize)
	cBuffer := make([]int32, pixSize)
	yMin := make([]int32, dim)

	var tBuffer []*Span
	var spans *SpanPool

	if transparent {
		tBuffer = make([]*Span, pixSize)
		spans = NewSpanPool()
	}

	renderer = &Renderer{
		width:   width,
		height:  height,
		yBuffer: yBuffer,
		cBuffer: cBuffer,
		yMin:    yMin,
		tBuffer: tBuffer,
		spans:   spans}

	renderer.initBuffers()
	return
}

func (r *Renderer) SetPos(xOfs, zOfs int16) {
	r.xOfs = xOfs
	r.zOfs = zOfs
}

func (r *Renderer) GetPos() (int16, int16) {
	return r.xOfs, r.zOfs
}

func (r *Renderer) initBuffers() {
	yb := r.yBuffer
	for i := range yb {
		yb[i] = math.MinInt32
	}

	cb := r.cBuffer
	for i := range cb {
		cb[i] = -1
	}

	ym := r.yMin
	for i := range ym {
		ym[i] = math.MinInt32
	}
}

func (r *Renderer) Reset() {

	r.RejectedBlocks = 0

	if r.SolidBlocks > 0 || r.TransparentBlocks > 0 {
		r.SolidBlocks = 0
		r.initBuffers()
	}

	if r.TransparentBlocks > 0 {
		r.TransparentBlocks = 0

		tb := r.tBuffer
		for i, t := range tb {
			if t != nil {
				r.spans.FreeAll(t)
				tb[i] = nil
			}
		}
	}
}

func (r *Renderer) IsFilled() bool {
	for _, y := range r.yMin {
		if y == math.MinInt32 {
			return false
		}
	}
	return true
}

func (r *Renderer) IsEmpty() bool {
	return r.SolidBlocks == 0 && r.TransparentBlocks == 0
}

// down goes down the y direction in a block from top to bottom.
// In its loop it copies the logic of Block.Content pulling some
// things like the version check and common indexing out to
// save some cycles.
func down(db *DecodedBlock, x, y, z int) (int32, int) {
	mc := db.MapContent
	switch {
	case db.Version >= 24:
		for sliver := (z<<8 + x) << 1; y >= 0; y-- {
			pos := sliver + y<<5
			content := int32(mc[pos])<<8 | int32(mc[pos+1])
			if content != db.AirID && content != db.IgnoreID {
				if c, found := db.IndexMap[content]; found {
					return c, y
				}
			}
		}
	case db.Version >= 20:
		for sliver := z<<8 + x; y >= 0; y-- {
			pos := sliver + y<<4
			var content int32
			if c := mc[pos]; c <= 0x80 {
				content = int32(c)
			} else {
				content = int32(c)<<4 | int32(mc[pos+0x2000])>>4
			}
			if content != db.AirID && content != db.IgnoreID {
				if c, found := db.IndexMap[content]; found {
					return c, y
				}
			}
		}
	}
	return -1, -1
}

func (r *Renderer) RenderBlock(block *Block, colors *Colors) (err error) {

	bx := block.Coord.X - r.xOfs
	bz := block.Coord.Z - r.zOfs

	// We do not need to render the block if the whole 16x16 area
	// is already filled and the block is strictly below.
	blockY := int32(block.Coord.Y) << 4
	pos := int(bz)*r.width + int(bx)
	if blockY < r.yMin[pos] {
		r.RejectedBlocks++
		return
	}

	// Decoding is pretty expensive so do it that late.
	var db *DecodedBlock
	if db, err = NewDecodedBlock(block.Data, colors); err != nil {
		return
	}

	if db.AirOnly() {
		r.RejectedBlocks++
		return
	}

	w := r.width << 4
	ofs := int(bz)*w<<4 + int(bx)<<4
	yB := r.yBuffer
	yMin := int32(math.MaxInt32)

	if db.Transparent && r.tBuffer != nil {
		r.TransparentBlocks++

		for z := 0; z < 16; z++ {
			for x := 0; x < 16; x++ {
				currentY := yB[ofs]
				if currentY < blockY {
					var c int32
					for y := 15; ; y-- {
						if c, y = down(db, x, y, z); y < 0 {
							break
						}
						cY := blockY + int32(y)

						if colors.IsTransparent(c) {
							r.tBuffer[ofs] = r.spans.Insert(r.tBuffer[ofs], cY, c)
							// We need to continue to go down because we
							// can see through this node.
						} else {
							r.cBuffer[ofs] = c
							currentY = cY
							yB[ofs] = currentY
							break
						}
					}
				}
				if currentY < yMin {
					yMin = currentY
				}
				ofs++
			}
			ofs += w - 16
		}

	} else {
		r.SolidBlocks++
		for z := 0; z < 16; z++ {
			for x := 0; x < 16; x++ {
				currentY := yB[ofs]
				if currentY < blockY {
					if c, y := down(db, x, 15, z); y >= 0 {
						r.cBuffer[ofs] = c
						currentY = blockY + int32(y)
						yB[ofs] = currentY
					}
				}
				if currentY < yMin {
					yMin = currentY
				}
				ofs++
			}
			ofs += w - 16
		}
	}

	r.yMin[pos] = yMin

	return
}

func (r *Renderer) CreateImage(colors []color.RGBA, background color.RGBA) *image.RGBA {
	pw, ph := r.width<<4, r.height<<4
	image := image.NewRGBA(image.Rect(0, 0, pw, ph))
	ofs, numCols := 0, int32(len(colors))
	for z := ph - 1; z >= 0; z-- {
		for x := 0; x < pw; x++ {
			colIdx := r.cBuffer[ofs]
			if colIdx >= 0 && colIdx < numCols {
				image.Set(x, z, colors[colIdx])
			} else {
				image.Set(x, z, background)
			}
			ofs++
		}
	}
	return image
}

func safeColor(x int32) uint8 {
	switch {
	case x < 0:
		return 0
	case x > 255:
		return 255
	default:
		return uint8(x)
	}
}

func (r *Renderer) CreateShadedImage(
	xOfs, zOfs, width, height int,
	cols *Colors, background color.RGBA) *image.RGBA {

	image := image.NewRGBA(image.Rect(0, 0, width, height))

	pw := r.width << 4

	cs := cols.Colors

	ofs, numCols := zOfs*pw+xOfs, int32(len(cs))

	stride := pw - width

	istride := image.Stride + 4*width

	iofs := image.PixOffset(0, height-1)

	pix := image.Pix

	if r.TransparentBlocks > 0 { // Fast path for transparent images.
		for z := height - 1; z >= 0; z-- {
			for x := 0; x < width; x++ {
				colIdx := r.cBuffer[ofs]
				if colIdx < 0 || colIdx >= numCols {
					pix[iofs] = background.R
					pix[iofs+1] = background.G
					pix[iofs+2] = background.B
					pix[iofs+3] = 0xff
				} else {
					y := r.yBuffer[ofs]
					t := r.tBuffer[ofs]

					opaque := t == nil || t.Top() < y

					var y1, y2 int32

					if x == 0 {
						y1 = y
					} else {
						y1 = r.yBuffer[ofs-1]
						if opaque {
							if s := r.tBuffer[ofs-1]; s != nil {
								y1 = max32(y1, s.Top())
							}
						}
					}
					if z == 0 {
						y2 = y
					} else {
						y2 = r.yBuffer[ofs+pw]
						if opaque {
							if s := r.tBuffer[ofs+pw]; s != nil {
								y1 = max32(y1, s.Top())
							}
						}
					}
					d := ((y - y1) + (y - y2)) * 12
					if d > 36 {
						d = 36
					}
					col := cs[colIdx]
					col = color.RGBA{
						R: safeColor(int32(col.R) + d),
						G: safeColor(int32(col.G) + d),
						B: safeColor(int32(col.B) + d),
						A: 0xff}
					if !opaque {
						col = cols.BlendColors(t, col, y)
					}
					pix[iofs] = col.R
					pix[iofs+1] = col.G
					pix[iofs+2] = col.B
					pix[iofs+3] = col.A
				}
				iofs += 4
				ofs++
			}
			ofs += stride
			iofs -= istride
		}

	} else { // Solid images.
		for z := height - 1; z >= 0; z-- {
			for x := 0; x < width; x++ {
				colIdx := r.cBuffer[ofs]
				if colIdx < 0 || colIdx >= numCols {
					pix[iofs] = background.R
					pix[iofs+1] = background.G
					pix[iofs+2] = background.B
					pix[iofs+3] = 0xff
				} else {
					var y, y1, y2 int32
					y = r.yBuffer[ofs]
					if x == 0 {
						y1 = y
					} else {
						y1 = r.yBuffer[ofs-1]
					}
					if z == 0 {
						y2 = y
					} else {
						y2 = r.yBuffer[ofs+pw]
					}
					d := ((y - y1) + (y - y2)) * 12
					if d > 36 {
						d = 36
					}
					col := cs[colIdx]
					pix[iofs] = safeColor(int32(col.R) + d)
					pix[iofs+1] = safeColor(int32(col.G) + d)
					pix[iofs+2] = safeColor(int32(col.B) + d)
					pix[iofs+3] = 0xff
				}
				iofs += 4
				ofs++
			}
			ofs += stride
			iofs -= istride
		}
	}
	return image
}