// 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 shareable

import (
	"fmt"
	"image/color"
	"runtime"

	"github.com/hajimehoshi/ebiten/internal/affine"
	"github.com/hajimehoshi/ebiten/internal/graphics"
	"github.com/hajimehoshi/ebiten/internal/opengl"
	"github.com/hajimehoshi/ebiten/internal/packing"
	"github.com/hajimehoshi/ebiten/internal/restorable"
	"github.com/hajimehoshi/ebiten/internal/sync"
)

type backend struct {
	restorable *restorable.Image

	// If page is nil, the backend is not shared.
	page *packing.Page
}

func (b *backend) TryAlloc(width, height int) (*packing.Node, bool) {
	// If the region is allocated without any extention, it's fine.
	if n := b.page.Alloc(width, height); n != nil {
		return n, true
	}

	// Simulate the extending the page and calculate the appropriate page size.
	page := b.page.Clone()
	nExtended := 0
	for {
		if !page.Extend() {
			// The page can't be extended any more. Return as failure.
			return nil, false
		}
		nExtended++
		if n := page.Alloc(width, height); n != nil {
			break
		}
	}

	for i := 0; i < nExtended; i++ {
		b.page.Extend()
	}
	s := b.page.Size()
	newImg := restorable.NewImage(s, s, false)
	oldImg := b.restorable
	w, h := oldImg.Size()
	newImg.DrawImage(oldImg, 0, 0, w, h, nil, nil, opengl.CompositeModeCopy, graphics.FilterNearest)
	oldImg.Dispose()
	b.restorable = newImg

	n := b.page.Alloc(width, height)
	if n == nil {
		panic("not reached")
	}
	return n, true
}

var (
	// backendsM is a mutex for critical sections of the backend and packing.Node objects.
	backendsM sync.Mutex

	// theBackends is a set of actually shared images.
	theBackends = []*backend{}
)

type Image struct {
	backend *backend

	// If node is nil, the image is not shared.
	node *packing.Node
}

func (i *Image) ensureNotShared() {
	if i.node == nil {
		return
	}

	x, y, w, h := i.region()
	newImg := restorable.NewImage(w, h, false)
	newImg.DrawImage(i.backend.restorable, x, y, x+w, y+h, nil, nil, opengl.CompositeModeCopy, graphics.FilterNearest)

	i.dispose()
	i.backend = &backend{
		restorable: newImg,
	}
}

func (i *Image) region() (x, y, width, height int) {
	if i.node == nil {
		w, h := i.backend.restorable.Size()
		return 0, 0, w, h
	}
	return i.node.Region()
}

func (i *Image) Size() (width, height int) {
	backendsM.Lock()
	defer backendsM.Unlock()
	_, _, w, h := i.region()
	return w, h
}

func (i *Image) DrawImage(img *Image, sx0, sy0, sx1, sy1 int, geom *affine.GeoM, colorm *affine.ColorM, mode opengl.CompositeMode, filter graphics.Filter) {
	backendsM.Lock()
	defer backendsM.Unlock()
	i.ensureNotShared()

	// Compare i and img after ensuring i is not shared, or
	// i and img might share the same texture even though i != img.
	if i.backend.restorable == img.backend.restorable {
		panic("shareable: Image.DrawImage: img must be different from the receiver")
	}

	dx, dy, _, _ := img.region()
	sx0 += dx
	sy0 += dy
	sx1 += dx
	sy1 += dy
	i.backend.restorable.DrawImage(img.backend.restorable, sx0, sy0, sx1, sy1, geom, colorm, mode, filter)
}

func (i *Image) ReplacePixels(p []byte) {
	backendsM.Lock()
	defer backendsM.Unlock()

	x, y, w, h := i.region()
	if l := 4 * w * h; len(p) != l {
		panic(fmt.Sprintf("shareable: len(p) was %d but must be %d", len(p), l))
	}
	i.backend.restorable.ReplacePixels(p, x, y, w, h)
}

func (i *Image) At(x, y int) (color.Color, error) {
	backendsM.Lock()
	defer backendsM.Unlock()

	ox, oy, w, h := i.region()
	if x < 0 || y < 0 || x >= w || y >= h {
		return color.RGBA{}, nil
	}

	clr, err := i.backend.restorable.At(x+ox, y+oy)
	return clr, err
}

func (i *Image) isDisposed() bool {
	return i.backend == nil
}

func (i *Image) Dispose() {
	backendsM.Lock()
	defer backendsM.Unlock()
	i.dispose()
}

func (i *Image) dispose() {
	if i.isDisposed() {
		return
	}

	defer func() {
		i.backend = nil
		i.node = nil
		runtime.SetFinalizer(i, nil)
	}()

	if i.node == nil {
		i.backend.restorable.Dispose()
		return
	}

	i.backend.page.Free(i.node)
	if !i.backend.page.IsEmpty() {
		// As this part can be reused, this should be cleared explicitly.
		i.backend.restorable.Clear(i.region())
		return
	}

	i.backend.restorable.Dispose()
	index := -1
	for idx, sh := range theBackends {
		if sh == i.backend {
			index = idx
			break
		}
	}
	if index == -1 {
		panic("not reached")
	}
	theBackends = append(theBackends[:index], theBackends[index+1:]...)
}

func (i *Image) IsInvalidated() (bool, error) {
	backendsM.Lock()
	defer backendsM.Unlock()
	v, err := i.backend.restorable.IsInvalidated()
	return v, err
}

func NewImage(width, height int) *Image {
	const (
		initSize = 1024
		maxSize  = 4096
	)

	backendsM.Lock()
	defer backendsM.Unlock()

	if width > maxSize || height > maxSize {
		b := &backend{
			restorable: restorable.NewImage(width, height, false),
		}
		return &Image{
			backend: b,
		}
	}

	for _, b := range theBackends {
		if n, ok := b.TryAlloc(width, height); ok {
			return &Image{
				backend: b,
				node:    n,
			}
		}
	}
	size := initSize
	for width > size || height > size {
		if size == maxSize {
			panic("not reached")
		}
		size *= 2
	}

	b := &backend{
		restorable: restorable.NewImage(size, size, false),
		page:       packing.NewPage(size, maxSize),
	}
	theBackends = append(theBackends, b)

	n := b.page.Alloc(width, height)
	if n == nil {
		panic("not reached")
	}
	i := &Image{
		backend: b,
		node:    n,
	}
	runtime.SetFinalizer(i, (*Image).Dispose)
	return i
}

func NewVolatileImage(width, height int) *Image {
	backendsM.Lock()
	defer backendsM.Unlock()

	r := restorable.NewImage(width, height, true)
	i := &Image{
		backend: &backend{
			restorable: r,
		},
	}
	runtime.SetFinalizer(i, (*Image).Dispose)
	return i
}

func NewScreenFramebufferImage(width, height int) *Image {
	backendsM.Lock()
	defer backendsM.Unlock()

	r := restorable.NewScreenFramebufferImage(width, height)
	i := &Image{
		backend: &backend{
			restorable: r,
		},
	}
	runtime.SetFinalizer(i, (*Image).Dispose)
	return i
}

func InitializeGLState() error {
	backendsM.Lock()
	defer backendsM.Unlock()
	return restorable.InitializeGLState()
}

func ResolveStaleImages() error {
	backendsM.Lock()
	defer backendsM.Unlock()
	return restorable.ResolveStaleImages()
}

func IsRestoringEnabled() bool {
	// As IsRestoringEnabled is an immutable state, no need to lock here.
	return restorable.IsRestoringEnabled()
}

func Restore() error {
	backendsM.Lock()
	defer backendsM.Unlock()
	return restorable.Restore()
}

func BackendNumForTesting() int {
	backendsM.Lock()
	defer backendsM.Unlock()
	return len(theBackends)
}