package main

import (
	"bytes"
	"context"
	"encoding/base64"
	"fmt"
	"image"
	"image/png"
	_ "image/gif"
	_ "image/jpeg"

	_ "github.com/biessek/golang-ico"
	_ "golang.org/x/image/webp"
)

// convertIconToBase64PNG downloads an icon from S3, converts it to PNG, and returns base64-encoded data.
func convertIconToBase64PNG(ctx context.Context, s3Key string, iconsBucket string) (encoded string, width, height int, err error) {
	data, err := s3Download(ctx, iconsBucket, s3Key)
	if err != nil {
		return "", 0, 0, fmt.Errorf("s3 download: %w", err)
	}

	// Check for SVG (can't decode to raster without external deps)
	if isSVG(data) {
		return "", 0, 0, fmt.Errorf("svg not supported")
	}

	// image.Decode handles PNG, GIF, JPEG, WebP, BMP, and ICO (via registered decoders)
	img, _, err := image.Decode(bytes.NewReader(data))
	if err != nil {
		return "", 0, 0, fmt.Errorf("decode: %w", err)
	}

	// Downscale icons >128px to 32x32 to keep bundle sizes reasonable
	bounds := img.Bounds()
	w, h := bounds.Dx(), bounds.Dy()
	if w > 128 || h > 128 {
		img = resizeNearestNeighbor(img, 32, 32)
		w, h = 32, 32
	}

	// Re-encode as PNG
	var pngBuf bytes.Buffer
	if err := png.Encode(&pngBuf, img); err != nil {
		return "", 0, 0, fmt.Errorf("png encode: %w", err)
	}

	encoded = base64.StdEncoding.EncodeToString(pngBuf.Bytes())
	return encoded, w, h, nil
}

// resizeNearestNeighbor does a simple nearest-neighbor resize.
func resizeNearestNeighbor(src image.Image, dstW, dstH int) image.Image {
	srcBounds := src.Bounds()
	srcW := srcBounds.Dx()
	srcH := srcBounds.Dy()
	dst := image.NewRGBA(image.Rect(0, 0, dstW, dstH))
	for y := 0; y < dstH; y++ {
		srcY := srcBounds.Min.Y + y*srcH/dstH
		for x := 0; x < dstW; x++ {
			srcX := srcBounds.Min.X + x*srcW/dstW
			dst.Set(x, y, src.At(srcX, srcY))
		}
	}
	return dst
}

func isSVG(data []byte) bool {
	if len(data) < 5 {
		return false
	}
	header := data[:min(256, len(data))]
	return bytes.Contains(header, []byte("<svg")) || bytes.Contains(header, []byte("<?xml"))
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}