// Copyright 2019 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package buffered

import (
	"fmt"
	"image"

	"github.com/hajimehoshi/ebiten/v2/internal/atlas"
	"github.com/hajimehoshi/ebiten/v2/internal/graphics"
	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver"
	"github.com/hajimehoshi/ebiten/v2/internal/restorable"
)

var whiteImage *Image

func init() {
	whiteImage = NewImage(3, 3, atlas.ImageTypeRegular)
	pix := make([]byte, 4*3*3)
	for i := range pix {
		pix[i] = 0xff
	}
	whiteImage.WritePixels(pix, image.Rect(0, 0, 3, 3))
}

type Image struct {
	img    *atlas.Image
	width  int
	height int

	// dotsBuffer is a buffer for drawing a lot of dots.
	// An entry in this map is the primary data of pixels for ReadPixels.
	dotsBuffer map[image.Point][4]byte

	// pixels is cached pixels for ReadPixels.
	// pixels might be out of sync with GPU.
	// The data of pixels is the secondary data of pixels for ReadPixels.
	//
	// pixels is always nil when restorable.AlwaysReadPixelsFromGPU() returns false.
	pixels []byte

	// pixelsUnsynced represents whether the pixels in CPU and GPU are not synced.
	pixelsUnsynced bool
}

func NewImage(width, height int, imageType atlas.ImageType) *Image {
	return &Image{
		img:    atlas.NewImage(width, height, imageType),
		width:  width,
		height: height,
	}
}

func (i *Image) Deallocate() {
	i.img.Deallocate()
	i.dotsBuffer = nil
	i.pixels = nil
	i.pixelsUnsynced = false
}

func (i *Image) ReadPixels(graphicsDriver graphicsdriver.Graphics, pixels []byte, region image.Rectangle) (bool, error) {
	if region.Dx() == 1 && region.Dy() == 1 {
		if c, ok := i.dotsBuffer[region.Min]; ok {
			copy(pixels, c[:])
			return true, nil
		}
	}

	// If restorable.AlwaysReadPixelsFromGPU() returns false, the pixel data is cached in the restorable package.
	if !restorable.AlwaysReadPixelsFromGPU() {
		i.syncPixelsIfNeeded()
		ok, err := i.img.ReadPixels(graphicsDriver, pixels, region)
		if err != nil {
			return false, err
		}
		return ok, nil
	}

	// Do not call syncPixelsIfNeeded here. This would slow (image/draw).Draw.
	// See ebiten.TestImageDrawOver.

	if i.pixels == nil {
		pix := make([]byte, 4*i.width*i.height)
		ok, err := i.img.ReadPixels(graphicsDriver, pix, image.Rect(0, 0, i.width, i.height))
		if err != nil {
			return false, err
		}
		if !ok {
			return false, nil
		}
		i.pixels = pix
	}

	if len(i.dotsBuffer) > 0 {
		for pos, clr := range i.dotsBuffer {
			idx := 4 * (pos.Y*i.width + pos.X)
			i.pixels[idx] = clr[0]
			i.pixels[idx+1] = clr[1]
			i.pixels[idx+2] = clr[2]
			i.pixels[idx+3] = clr[3]
			delete(i.dotsBuffer, pos)
		}
		i.pixelsUnsynced = true
	}

	lineWidth := 4 * region.Dx()
	for j := 0; j < region.Dy(); j++ {
		dstX := 4 * j * region.Dx()
		srcX := 4 * ((region.Min.Y+j)*i.width + region.Min.X)
		copy(pixels[dstX:dstX+lineWidth], i.pixels[srcX:srcX+lineWidth])
	}

	return true, nil
}

func (i *Image) DumpScreenshot(graphicsDriver graphicsdriver.Graphics, name string, blackbg bool) (string, error) {
	i.syncPixelsIfNeeded()
	return i.img.DumpScreenshot(graphicsDriver, name, blackbg)
}

// WritePixels replaces the pixels at the specified region.
func (i *Image) WritePixels(pix []byte, region image.Rectangle) {
	if l := 4 * region.Dx() * region.Dy(); len(pix) != l {
		panic(fmt.Sprintf("buffered: len(pix) was %d but must be %d", len(pix), l))
	}

	// Writing one pixel is a special case.
	// Do not write pixels in GPU, as (image/draw).Image's functions might call WritePixels with pixels one by one.
	if region.Dx() == 1 && region.Dy() == 1 {
		// If i.pixels exists, update this instead of adding an entry to dotsBuffer.
		if i.pixels != nil {
			idx := 4 * (region.Min.Y*i.width + region.Min.X)
			i.pixels[idx] = pix[0]
			i.pixels[idx+1] = pix[1]
			i.pixels[idx+2] = pix[2]
			i.pixels[idx+3] = pix[3]
			i.pixelsUnsynced = true
			delete(i.dotsBuffer, region.Min)
			return
		}

		if i.dotsBuffer == nil {
			i.dotsBuffer = map[image.Point][4]byte{}
		}

		var clr [4]byte
		copy(clr[:], pix)
		i.dotsBuffer[region.Min] = clr

		if len(i.dotsBuffer) >= 10000 {
			i.syncPixelsIfNeeded()
		}
		return
	}

	// If i.pixels is not nil, this indicates ReadPixels is called and might be called again later.
	// Keep and update the pixels data in this case.
	if i.pixels != nil {
		lineWidth := 4 * region.Dx()
		for j := 0; j < region.Dy(); j++ {
			dstX := 4 * ((region.Min.Y+j)*i.width + region.Min.X)
			srcX := 4 * j * region.Dx()
			copy(i.pixels[dstX:dstX+lineWidth], pix[srcX:srcX+lineWidth])
		}
		// pixelsUnsynced can NOT be set false as the outside pixels of the region is not written by WritePixels here.
		// See the test TestUnsyncedPixels.
	}

	// Even if i.pixels is nil, do not create a pixel cache.
	// It is in theroy possible to copy the argument pixels, but this tends to consume a lot of memory.
	// Avoid this unless ReadPixels is called.

	// Remove entries in the dots buffer that are overwritten by this WritePixels call.
	for pos := range i.dotsBuffer {
		if !pos.In(region) {
			continue
		}
		delete(i.dotsBuffer, pos)
	}

	i.img.WritePixels(pix, region)
}

// DrawTriangles draws the src image with the given vertices.
//
// Copying vertices and indices is the caller's responsibility.
func (i *Image) DrawTriangles(srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *atlas.Shader, uniforms []uint32, fillRule graphicsdriver.FillRule, hint restorable.Hint) {
	for _, src := range srcs {
		if i == src {
			panic("buffered: Image.DrawTriangles: source images must be different from the receiver")
		}
		if src != nil {
			// src's pixels have to be synced between CPU and GPU,
			// but doesn't have to be cleared since src is not modified in this function.
			src.syncPixelsIfNeeded()
		}
	}

	i.syncPixelsIfNeeded()

	var imgs [graphics.ShaderSrcImageCount]*atlas.Image
	for i, img := range srcs {
		if img == nil {
			continue
		}
		imgs[i] = img.img
	}

	i.img.DrawTriangles(imgs, vertices, indices, blend, dstRegion, srcRegions, shader, uniforms, fillRule, hint)

	// After rendering, the pixel cache is no longer valid.
	i.pixels = nil
}

// syncPixelsIfNeeded syncs the pixels between CPU and GPU.
// After syncPixelsIfNeeded, dotsBuffer is cleared, but pixels might remain.
func (i *Image) syncPixelsIfNeeded() {
	if i.pixelsUnsynced {
		// If this image already has pixels, use WritePixels instead of DrawTriangles for efficiency.
		for pos, clr := range i.dotsBuffer {
			idx := 4 * (pos.Y*i.width + pos.X)
			i.pixels[idx] = clr[0]
			i.pixels[idx+1] = clr[1]
			i.pixels[idx+2] = clr[2]
			i.pixels[idx+3] = clr[3]
			delete(i.dotsBuffer, pos)
		}
		i.img.WritePixels(i.pixels, image.Rect(0, 0, i.width, i.height))
		i.pixelsUnsynced = false
		return
	}

	if len(i.dotsBuffer) == 0 {
		return
	}

	l := len(i.dotsBuffer)
	vs := make([]float32, l*4*graphics.VertexFloatCount)
	is := make([]uint32, l*6)
	sx, sy := float32(1), float32(1)
	var idx int
	for p, c := range i.dotsBuffer {
		dx := float32(p.X)
		dy := float32(p.Y)
		crf := float32(c[0]) / 0xff
		cgf := float32(c[1]) / 0xff
		cbf := float32(c[2]) / 0xff
		caf := float32(c[3]) / 0xff

		vidx := 4 * idx
		iidx := 6 * idx

		vs[graphics.VertexFloatCount*vidx] = dx
		vs[graphics.VertexFloatCount*vidx+1] = dy
		vs[graphics.VertexFloatCount*vidx+2] = sx
		vs[graphics.VertexFloatCount*vidx+3] = sy
		vs[graphics.VertexFloatCount*vidx+4] = crf
		vs[graphics.VertexFloatCount*vidx+5] = cgf
		vs[graphics.VertexFloatCount*vidx+6] = cbf
		vs[graphics.VertexFloatCount*vidx+7] = caf

		vs[graphics.VertexFloatCount*(vidx+1)] = dx + 1
		vs[graphics.VertexFloatCount*(vidx+1)+1] = dy
		vs[graphics.VertexFloatCount*(vidx+1)+2] = sx + 1
		vs[graphics.VertexFloatCount*(vidx+1)+3] = sy
		vs[graphics.VertexFloatCount*(vidx+1)+4] = crf
		vs[graphics.VertexFloatCount*(vidx+1)+5] = cgf
		vs[graphics.VertexFloatCount*(vidx+1)+6] = cbf
		vs[graphics.VertexFloatCount*(vidx+1)+7] = caf

		vs[graphics.VertexFloatCount*(vidx+2)] = dx
		vs[graphics.VertexFloatCount*(vidx+2)+1] = dy + 1
		vs[graphics.VertexFloatCount*(vidx+2)+2] = sx
		vs[graphics.VertexFloatCount*(vidx+2)+3] = sy + 1
		vs[graphics.VertexFloatCount*(vidx+2)+4] = crf
		vs[graphics.VertexFloatCount*(vidx+2)+5] = cgf
		vs[graphics.VertexFloatCount*(vidx+2)+6] = cbf
		vs[graphics.VertexFloatCount*(vidx+2)+7] = caf

		vs[graphics.VertexFloatCount*(vidx+3)] = dx + 1
		vs[graphics.VertexFloatCount*(vidx+3)+1] = dy + 1
		vs[graphics.VertexFloatCount*(vidx+3)+2] = sx + 1
		vs[graphics.VertexFloatCount*(vidx+3)+3] = sy + 1
		vs[graphics.VertexFloatCount*(vidx+3)+4] = crf
		vs[graphics.VertexFloatCount*(vidx+3)+5] = cgf
		vs[graphics.VertexFloatCount*(vidx+3)+6] = cbf
		vs[graphics.VertexFloatCount*(vidx+3)+7] = caf

		is[iidx] = uint32(vidx)
		is[iidx+1] = uint32(vidx + 1)
		is[iidx+2] = uint32(vidx + 2)
		is[iidx+3] = uint32(vidx + 1)
		is[iidx+4] = uint32(vidx + 2)
		is[iidx+5] = uint32(vidx + 3)

		idx++
	}

	srcs := [graphics.ShaderSrcImageCount]*atlas.Image{whiteImage.img}
	dr := image.Rect(0, 0, i.width, i.height)
	blend := graphicsdriver.BlendCopy
	i.img.DrawTriangles(srcs, vs, is, blend, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillRuleFillAll, restorable.HintNone)

	// TODO: Use clear if Go 1.21 is available.
	for pos := range i.dotsBuffer {
		delete(i.dotsBuffer, pos)
	}
}