// Copyright 2014 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 (
	"container/heap"
	"image"
	"image/color"
	"math"
)

type Area struct {
	X1, Z1 int16
	X2, Z2 int16
}

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

type YOrder struct {
	Renderer *Renderer
	blocks   []*Block
	capacity int
}

func NewYOrder(renderer *Renderer, capacity int) *YOrder {
	return &YOrder{
		Renderer: renderer,
		blocks:   make([]*Block, 0, capacity),
		capacity: capacity}
}

func (yo *YOrder) Reset() {
	yo.blocks = yo.blocks[0:0]
}

func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func copyData(data []byte) []byte {
	l := len(data)
	ndata := make([]byte, l, max(l, 8*1024))
	copy(ndata, data)
	return ndata
}

func (yo *YOrder) RenderBlock(block *Block, colors *Colors) (err error) {
	var nblock *Block
	if len(yo.blocks) == yo.capacity {
		oblock := yo.blocks[0]
		if oblock.Coord.Y < block.Coord.Y {
			// New one is above highest old. Directly render new.
			err = yo.Renderer.RenderBlock(block, colors)
			return
		}
		// Render old one. Store copy of new in heap.
		heap.Pop(yo)
		err = yo.Renderer.RenderBlock(oblock, colors)
		l := len(block.Data)
		if cap(oblock.Data) < l {
			oblock.Data = make([]byte, l, max(l, 8*1024))
		} else {
			oblock.Data = oblock.Data[0:l]
		}
		copy(oblock.Data, block.Data)
		oblock.Coord = block.Coord
		nblock = oblock
	} else {
		nblock = &Block{Coord: block.Coord, Data: copyData(block.Data)}
	}

	heap.Push(yo, nblock)
	return
}

func (yo *YOrder) Drain(colors *Colors) (err error) {
	for len(yo.blocks) > 0 {
		if err = yo.Renderer.RenderBlock(heap.Pop(yo).(*Block), colors); err != nil {
			return
		}
	}
	return
}

func (yo *YOrder) Len() int {
	return len(yo.blocks)
}

func (yo *YOrder) Swap(i, j int) {
	yo.blocks[i], yo.blocks[j] = yo.blocks[j], yo.blocks[i]
}

func (yo *YOrder) Less(i, j int) bool {
	// Reverse order intented.
	return yo.blocks[i].Coord.Y > yo.blocks[j].Coord.Y
}

func (yo *YOrder) Push(x interface{}) {
	yo.blocks = append(yo.blocks, x.(*Block))
}

func (yo *YOrder) Pop() (x interface{}) {
	l := len(yo.blocks)
	x = yo.blocks[l-1]
	yo.blocks = yo.blocks[0 : l-1]
	return x
}

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

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

	renderer.Reset()
	return
}

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

func (r *Renderer) Reset() {
	for i, n := 0, len(r.yBuffer); i < n; i++ {
		r.yBuffer[i] = math.MinInt32
		r.cBuffer[i] = -1
	}
	for i, n := 0, len(r.yMin); i < n; i++ {
		r.yMin[i] = math.MinInt32
	}
}

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

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
	}

	if db.Transparent {
		r.TransparentBlocks++
	} else {
		r.SolidBlocks++
	}

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

	yMin := int32(math.MaxInt32)
	for z := 0; z < 16; z++ {
		for x := 0; x < 16; x++ {
			currentY := yB[ofs]
			if currentY < blockY {
				for y := 15; y >= 0; y-- {
					if c, ok := db.Content(x, y, z); ok {
						r.cBuffer[ofs] = c
						currentY = blockY + int32(y)
						yB[ofs] = currentY
						break
					}
				}
			}
			if currentY < yMin {
				yMin = currentY
			}
			ofs++
		}
		ofs += w - 16
	}
	r.yMin[pos] = yMin

	return
}

func (a Area) Contains(x, z int16) bool {
	return x >= a.X1 && x <= a.X2 && z >= a.Z1 && z <= a.Z2
}

func (a Area) IsHigher() bool {
	return a.Z2-a.Z1 > a.X2-a.X1
}

func areasContain(areas []Area, x, z int16) bool {
	for _, r := range areas {
		if r.Contains(x, z) {
			return true
		}
	}
	return false
}

// Greedy algorithm to figure out a list of disjunct areas
// of free regions in the domain to the (x, z) block plane.
// oldAreas are searched and found free areas are appended
// to newAreas which ist return.
// This is useful to spatial query only blocks from db
// that are not below already rendered blocks.
func (r *Renderer) UncoveredAreas(newAreas, oldAreas []Area) []Area {
	yM := r.yMin

	// Scan old areas.
	for _, oldArea := range oldAreas {
		for z := oldArea.Z1; z <= oldArea.Z2; z++ {
			row := z * int16(r.width)
			for x := oldArea.X1; x <= oldArea.X2; x++ {
				// Uncovered and not in list of new areas?
				if yM[row+x] > math.MinInt32 || areasContain(newAreas, x, z) {
					continue
				}
				area := Area{X1: x, Z1: z, X2: x, Z2: z}
				// Try to extend the area in x and/or z till no further extension is possible.
				for extendDirs := 1 | 2; extendDirs != 0; {
					var xFirst bool
					// Try to extend in the direction with most gain
					// of blocks.
					if area.IsHigher() { // Higher means to win more blocks in x direction.
						xFirst = true
					}
				dirs:
					for i := 0; i < 2; i++ {
						if xFirst {
							// Extension in x possible?
							if extendDirs&1 == 1 {
								nx := area.X2 + 1
								if nx >= int16(r.width) {
									extendDirs &= ^1
									continue
								}
								// Scan line below current area if its fully free.
								for nz := area.Z1; nz <= area.Z2; nz++ {
									if yM[nz*int16(r.width)+nx] > math.MinInt32 || areasContain(newAreas, nx, nz) {
										extendDirs &= ^1
										continue dirs
									}
								}
								// free -> extend
								area.X2 = nx
							}
						} else if extendDirs&2 == 2 {
							// Symmetric case in z direction
							nz := area.Z2 + 1
							if nz >= int16(r.height) {
								extendDirs &= ^2
								continue
							}
							// Scan line right beside the area if its free.
							row2 := nz * int16(r.width)
							for nx := area.X1; nx <= area.X2; nx++ {
								if yM[row2+nx] > math.MinInt32 || areasContain(newAreas, nx, nz) {
									extendDirs &= ^2
									continue dirs
								}
							}
							area.Z2 = nz
						}
						// Switch to other search direction (x -> z or z -> x)
						xFirst = !xFirst
					}
				}
				// At this point the area is extended to max.
				newAreas = append(newAreas, area)
			}
		}
	}
	return newAreas
}

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,
	colors []color.RGBA, background color.RGBA) *image.RGBA {

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

	pw := r.width << 4

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

	stride := pw - width

	istride := image.Stride + 4*width

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

	pix := image.Pix

	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 := colors[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
}