// 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 ebiten

import (
	"image"
	"math"

	"github.com/hajimehoshi/ebiten/internal/driver"
	"github.com/hajimehoshi/ebiten/internal/graphics"
	"github.com/hajimehoshi/ebiten/internal/shareable"
)

type mipmap struct {
	orig *shareable.Image
	imgs map[image.Rectangle][]*shareable.Image
}

func newMipmap(s *shareable.Image) *mipmap {
	return &mipmap{
		orig: s,
		imgs: map[image.Rectangle][]*shareable.Image{},
	}
}

func (m *mipmap) original() *shareable.Image {
	return m.orig
}

func (m *mipmap) level(r image.Rectangle, level int) *shareable.Image {
	if level <= 0 {
		panic("ebiten: level must be positive at level")
	}

	imgs, ok := m.imgs[r]
	if !ok {
		imgs = []*shareable.Image{}
		m.imgs[r] = imgs
	}
	idx := level - 1

	size := r.Size()
	w, h := size.X, size.Y
	if len(imgs) > 0 {
		w, h = imgs[len(imgs)-1].Size()
	}

	for len(imgs) < idx+1 {
		if m.orig.IsVolatile() {
			panic("ebiten: mipmap images for a volatile image is not implemented yet")
		}

		w2 := w / 2
		h2 := h / 2
		if w2 == 0 || h2 == 0 {
			return nil
		}
		s := shareable.NewImage(w2, h2)
		var src *shareable.Image
		vs := vertexSlice(4)
		if l := len(imgs); l == 0 {
			src = m.orig
			graphics.PutQuadVertices(vs, src, r.Min.X, r.Min.Y, r.Max.X, r.Max.Y, 0.5, 0, 0, 0.5, 0, 0, 1, 1, 1, 1)
		} else {
			src = m.level(r, l)
			graphics.PutQuadVertices(vs, src, 0, 0, w, h, 0.5, 0, 0, 0.5, 0, 0, 1, 1, 1, 1)
		}
		is := graphics.QuadIndices()
		s.DrawTriangles(src, vs, is, nil, driver.CompositeModeCopy, driver.FilterLinear, driver.AddressClampToZero)
		imgs = append(imgs, s)
		w = w2
		h = h2
	}
	m.imgs[r] = imgs

	if len(imgs) <= idx {
		return nil
	}
	return imgs[idx]
}

func (m *mipmap) isDisposed() bool {
	return m.orig == nil
}

func (m *mipmap) dispose() {
	m.disposeMipmaps()
	m.orig.Dispose()
	m.orig = nil
}

func (m *mipmap) disposeMipmaps() {
	for _, a := range m.imgs {
		for _, img := range a {
			img.Dispose()
		}
	}
	for k := range m.imgs {
		delete(m.imgs, k)
	}
}

// mipmapLevel returns an appropriate mipmap level for the given determinant of a geometry matrix.
//
// mipmapLevel returns -1 if det is 0.
//
// mipmapLevel panics if det is NaN.
func mipmapLevel(det float32) int {
	if math.IsNaN(float64(det)) {
		panic("graphicsutil: det must be finite")
	}
	if det == 0 {
		return -1
	}

	d := math.Abs(float64(det))
	level := 0
	for d < 0.25 {
		level++
		d *= 4
	}
	return level
}