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package main

import (
	"bytes"
	"errors"
	"image"
	_ "image/gif"
	_ "image/jpeg"
	"image/png"
	"sync"

	"golang.org/x/image/draw"
	_ "golang.org/x/image/webp"
)

const avatarSize = 256

var decoding sync.Mutex

func cropAvatar(data []byte, x, y, size int) ([]byte, error) {
	cfg, _, err := image.DecodeConfig(bytes.NewReader(data))
	if err != nil {
		return nil, errors.New("Avatar must be a PNG, JPEG, GIF or WebP image")
	}
	if cfg.Width > 6000 || cfg.Height > 6000 || cfg.Width*cfg.Height > 16_000_000 {
		return nil, errors.New("Avatar image is too large, keep it under 16 megapixels")
	}
	decoding.Lock()
	defer decoding.Unlock()
	img, _, err := image.Decode(bytes.NewReader(data))
	if err != nil {
		return nil, errors.New("Avatar must be a PNG, JPEG, GIF or WebP image")
	}
	b := img.Bounds()
	if size <= 0 || size > b.Dx() || size > b.Dy() {
		size = min(b.Dx(), b.Dy())
		x = (b.Dx() - size) / 2
		y = (b.Dy() - size) / 2
	}
	x = max(0, min(x, b.Dx()-size))
	y = max(0, min(y, b.Dy()-size))
	src := image.Rect(b.Min.X+x, b.Min.Y+y, b.Min.X+x+size, b.Min.Y+y+size)
	dst := image.NewRGBA(image.Rect(0, 0, avatarSize, avatarSize))
	draw.CatmullRom.Scale(dst, dst.Bounds(), img, src, draw.Src, nil)
	var out bytes.Buffer
	if err := png.Encode(&out, dst); err != nil {
		return nil, err
	}
	return out.Bytes(), nil
}