/*
Copyright 2021 Josh Deprez

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 engine

import (
	"encoding/gob"
	"image"
	"io/fs"

	"github.com/hajimehoshi/ebiten/v2"
)

var (
	imageCache = make(map[assetKey]*ebiten.Image)

	// Ensure types satisfy interfaces.
	_ Loader = &ImageRef{}
)

func init() {
	gob.Register(&ImageRef{})
}

// ImageRef loads images from the AssetFS into *ebiten.Image form. It is your
// responsibility to import _ "image/..." for whatever format the files are in,
// and to load it (either return it as a subcomponent from Scan so that Game
// will Load it, or call Load yourself).
type ImageRef struct {
	Path string

	image *ebiten.Image
}

// Image returns the image, or nil if not loaded. Multiple distinct ImageRefs
// can use the same path efficiently.
func (r *ImageRef) Image() *ebiten.Image {
	return r.image
}

// Load loads the image. Load is required before Image returns. Loading the same
// path multiple times uses a cache to return the same image.
func (r *ImageRef) Load(assets fs.FS) error {
	// Fast path load from cache
	r.image = imageCache[assetKey{assets, r.Path}]
	if r.image != nil {
		return nil
	}
	// Slow path
	f, err := assets.Open(r.Path)
	if err != nil {
		return err
	}
	defer f.Close()
	i, _, err := image.Decode(f)
	if err != nil {
		return err
	}
	r.image = ebiten.NewImageFromImage(i)
	imageCache[assetKey{assets, r.Path}] = r.image
	return nil
}

func (r *ImageRef) String() string { return "ImageRef{" + r.Path + "}" }