// Copyright 2018 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 mipmap

import (
	"fmt"
	"image"
	"math"

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

func canUseMipmap(imageType atlas.ImageType) bool {
	switch imageType {
	case atlas.ImageTypeRegular, atlas.ImageTypeUnmanaged:
		return true
	}
	return false
}

// Mipmap is a set of buffered.Image sorted by the order of mipmap level.
// The level 0 image is a regular image and higher-level images are used for mipmap.
type Mipmap struct {
	width     int
	height    int
	imageType atlas.ImageType
	orig      *buffered.Image
	imgs      map[int]*buffered.Image
}

func New(width, height int, imageType atlas.ImageType) *Mipmap {
	return &Mipmap{
		width:     width,
		height:    height,
		orig:      buffered.NewImage(width, height, imageType),
		imageType: imageType,
	}
}

func (m *Mipmap) DumpScreenshot(graphicsDriver graphicsdriver.Graphics, name string, blackbg bool) (string, error) {
	return m.orig.DumpScreenshot(graphicsDriver, name, blackbg)
}

func (m *Mipmap) WritePixels(pix []byte, region image.Rectangle) {
	m.orig.WritePixels(pix, region)
	m.disposeMipmaps()
}

func (m *Mipmap) ReadPixels(graphicsDriver graphicsdriver.Graphics, pixels []byte, region image.Rectangle) error {
	return m.orig.ReadPixels(graphicsDriver, pixels, region)
}

func (m *Mipmap) DrawTriangles(srcs [graphics.ShaderImageCount]*Mipmap, vertices []float32, indices []uint16, blend graphicsdriver.Blend, dstRegion graphicsdriver.Region, srcRegions [graphics.ShaderImageCount]graphicsdriver.Region, shader *Shader, uniforms []uint32, evenOdd bool, canSkipMipmap bool) {
	if len(indices) == 0 {
		return
	}

	level := 0
	// TODO: Do we need to check all the sources' states of being volatile?
	if !canSkipMipmap && srcs[0] != nil && canUseMipmap(srcs[0].imageType) {
		level = math.MaxInt32
		for i := 0; i < len(indices)/3; i++ {
			const n = graphics.VertexFloatCount
			dx0 := vertices[n*indices[3*i]+0]
			dy0 := vertices[n*indices[3*i]+1]
			sx0 := vertices[n*indices[3*i]+2]
			sy0 := vertices[n*indices[3*i]+3]
			dx1 := vertices[n*indices[3*i+1]+0]
			dy1 := vertices[n*indices[3*i+1]+1]
			sx1 := vertices[n*indices[3*i+1]+2]
			sy1 := vertices[n*indices[3*i+1]+3]
			dx2 := vertices[n*indices[3*i+2]+0]
			dy2 := vertices[n*indices[3*i+2]+1]
			sx2 := vertices[n*indices[3*i+2]+2]
			sy2 := vertices[n*indices[3*i+2]+3]
			if l := mipmapLevelFromDistance(dx0, dy0, dx1, dy1, sx0, sy0, sx1, sy1); level > l {
				level = l
			}
			if l := mipmapLevelFromDistance(dx1, dy1, dx2, dy2, sx1, sy1, sx2, sy2); level > l {
				level = l
			}
			if l := mipmapLevelFromDistance(dx2, dy2, dx0, dy0, sx2, sy2, sx0, sy0); level > l {
				level = l
			}
		}
		if level == math.MaxInt32 {
			panic("mipmap: level must be calculated at least once but not")
		}
	}

	var imgs [graphics.ShaderImageCount]*buffered.Image
	for i, src := range srcs {
		if src == nil {
			continue
		}
		if level != 0 {
			if img := src.level(level); img != nil {
				const n = graphics.VertexFloatCount
				s := float32(pow2(level))
				for i := 0; i < len(vertices)/n; i++ {
					vertices[i*n+2] /= s
					vertices[i*n+3] /= s
				}
				imgs[i] = img
				continue
			}
		}
		imgs[i] = src.orig
	}

	m.orig.DrawTriangles(imgs, vertices, indices, blend, dstRegion, srcRegions, shader.shader, uniforms, evenOdd)
	m.disposeMipmaps()
}

func (m *Mipmap) setImg(level int, img *buffered.Image) {
	if m.imgs == nil {
		m.imgs = map[int]*buffered.Image{}
	}
	m.imgs[level] = img
}

func (m *Mipmap) level(level int) *buffered.Image {
	if level == 0 {
		panic("mipmap: level must be non-zero at level")
	}

	if !canUseMipmap(m.imageType) {
		panic("mipmap: mipmap images for a volatile or a screen image is not implemented yet")
	}

	if img, ok := m.imgs[level]; ok {
		return img
	}

	var src *buffered.Image
	vs := make([]float32, 4*graphics.VertexFloatCount)
	shader := NearestFilterShader
	switch {
	case level == 1:
		src = m.orig
		graphics.QuadVertices(vs, 0, 0, float32(m.width), float32(m.height), 0.5, 0, 0, 0.5, 0, 0, 1, 1, 1, 1)
		shader = LinearFilterShader
	case level > 1:
		src = m.level(level - 1)
		if src == nil {
			m.setImg(level, nil)
			return nil
		}
		w := sizeForLevel(m.width, level-1)
		h := sizeForLevel(m.height, level-1)
		graphics.QuadVertices(vs, 0, 0, float32(w), float32(h), 0.5, 0, 0, 0.5, 0, 0, 1, 1, 1, 1)
		shader = LinearFilterShader
	default:
		panic(fmt.Sprintf("mipmap: invalid level: %d", level))
	}
	is := graphics.QuadIndices()

	w2 := sizeForLevel(m.width, level-1)
	h2 := sizeForLevel(m.height, level-1)
	if w2 == 0 || h2 == 0 {
		m.setImg(level, nil)
		return nil
	}
	// buffered.NewImage panics with a too big size when actual allocation happens.
	// 4096 should be a safe size in most environments (#1399).
	// Unfortunately a precise max image size cannot be obtained here since this requires GPU access.
	if w2 > 4096 || h2 > 4096 {
		m.setImg(level, nil)
		return nil
	}

	s := buffered.NewImage(w2, h2, m.imageType)

	dstRegion := graphicsdriver.Region{
		X:      0,
		Y:      0,
		Width:  float32(w2),
		Height: float32(h2),
	}
	s.DrawTriangles([graphics.ShaderImageCount]*buffered.Image{src}, vs, is, graphicsdriver.BlendCopy, dstRegion, [graphics.ShaderImageCount]graphicsdriver.Region{}, shader.shader, nil, false)
	m.setImg(level, s)

	return m.imgs[level]
}

func sizeForLevel(x int, level int) int {
	for i := 0; i < level; i++ {
		x /= 2
		if x == 0 {
			return 0
		}
	}
	return x
}

func (m *Mipmap) MarkDisposed() {
	m.disposeMipmaps()
	m.orig.MarkDisposed()
	m.orig = nil
}

func (m *Mipmap) disposeMipmaps() {
	for _, img := range m.imgs {
		if img != nil {
			img.MarkDisposed()
		}
	}
	for k := range m.imgs {
		delete(m.imgs, k)
	}
}

// mipmapLevel returns an appropriate mipmap level for the given distance.
func mipmapLevelFromDistance(dx0, dy0, dx1, dy1, sx0, sy0, sx1, sy1 float32) int {
	const maxLevel = 6

	d := (dx1-dx0)*(dx1-dx0) + (dy1-dy0)*(dy1-dy0)
	s := (sx1-sx0)*(sx1-sx0) + (sy1-sy0)*(sy1-sy0)
	if s == 0 {
		return 0
	}
	scale := d / s

	// Scale can be infinite when the specified scale is extremely big (#1398).
	if math.IsInf(float64(scale), 0) {
		return 0
	}

	// Scale can be zero when the specified scale is extremely small (#1398).
	if scale == 0 {
		return 0
	}

	level := 0
	for scale < 0.25 {
		level++
		scale *= 4
	}

	if level > 0 {
		// If the image can be scaled into 0 size, adjust the level. (#839)
		w, h := int(sx1-sx0), int(sy1-sy0)
		for level >= 0 {
			s := 1 << uint(level)
			if (w > 0 && w/s == 0) || (h > 0 && h/s == 0) {
				level--
				continue
			}
			break
		}

		if level < 0 {
			// As the render source is too small, nothing is rendered.
			return 0
		}
	}

	if level > maxLevel {
		level = maxLevel
	}

	return level
}

func pow2(power int) float32 {
	x := 1
	return float32(x << uint(power))
}

type Shader struct {
	shader *buffered.Shader
}

func NewShader(ir *shaderir.Program) *Shader {
	return &Shader{
		shader: buffered.NewShader(ir),
	}
}

func (s *Shader) MarkDisposed() {
	s.shader.MarkDisposed()
	s.shader = nil
}

var (
	NearestFilterShader = &Shader{shader: buffered.NearestFilterShader}
	LinearFilterShader  = &Shader{shader: buffered.LinearFilterShader}
)