// Package avatar manages a user's profile photo: it normalises an uploaded
// image into square WebP variants and keeps them as journaled objects bound to
// the user, so the object ledger's garbage collection preserves them.
package avatar

import (
	"bytes"
	"errors"
	"image"

	"github.com/disintegration/imaging"
	"github.com/gen2brain/webp"
)

// Canonical avatar sizes. The small variant serves lists and headers; the large
// one serves the profile page.
const (
	SizeLarge = 512
	SizeSmall = 128
)

// maxUploadBytes caps an avatar upload. Avatars are small, so a generous
// general image limit would let a client stream needlessly.
const maxUploadBytes = 10 << 20

var errInvalidImage = errors.New("invalid image")

// normalize decodes an uploaded image and produces two square WebP variants.
// Decoding honours the EXIF orientation; re-encoding discards all metadata
// (including GPS), so the stored avatar carries none of the original's.
func normalize(data []byte) (large, small []byte, err error) {
	img, err := imaging.Decode(bytes.NewReader(data), imaging.AutoOrientation(true))
	if err != nil {
		return nil, nil, errInvalidImage
	}
	large, err = fillWebP(img, SizeLarge)
	if err != nil {
		return nil, nil, err
	}
	small, err = fillWebP(img, SizeSmall)
	if err != nil {
		return nil, nil, err
	}
	return large, small, nil
}

// fillWebP centre-crops the image to a square of the given size and encodes it
// as WebP.
func fillWebP(img image.Image, size int) ([]byte, error) {
	square := imaging.Fill(img, size, size, imaging.Center, imaging.Lanczos)
	var buf bytes.Buffer
	if err := webp.Encode(&buf, square, webp.Options{Quality: 82}); err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}