package media

import (
	"bytes"
	"context"
	"fmt"
	"os/exec"
	"strings"
)

const maxTelegramPhotoSize = 10 * 1024 * 1024 // 10 MB

// CompressImage compresses an image if it exceeds Telegram's 10 MB photo limit.
// It uses ImageMagick's magick command to convert via stdin/stdout.
// Returns the (possibly compressed) data, updated filename, and any error.
func CompressImage(ctx context.Context, data []byte, filename string) (out []byte, outName string, err error) {
	if len(data) <= maxTelegramPhotoSize {
		return data, filename, nil
	}

	// First attempt: just re-encode as JPEG with quality 85
	out, err = runMagick(ctx, data, "-quality", "85")
	if err != nil {
		return nil, "", fmt.Errorf("compress image: %w", err)
	}

	newFilename := replaceExt(filename, ".jpg")

	if len(out) <= maxTelegramPhotoSize {
		return out, newFilename, nil
	}

	// Second attempt: resize to 50% and quality 85
	out, err = runMagick(ctx, data, "-resize", "50%", "-quality", "85")
	if err != nil {
		return nil, "", fmt.Errorf("compress image with resize: %w", err)
	}

	if len(out) > maxTelegramPhotoSize {
		return nil, "", fmt.Errorf("image still too large after compression (%d bytes)", len(out))
	}

	return out, newFilename, nil
}

func runMagick(ctx context.Context, data []byte, args ...string) ([]byte, error) {
	cmdArgs := append([]string{"-"}, args...)
	cmdArgs = append(cmdArgs, "jpeg:-")

	cmd := exec.CommandContext(ctx, "magick", cmdArgs...)
	cmd.Stdin = bytes.NewReader(data)

	out, err := cmd.Output()
	if err != nil {
		return nil, fmt.Errorf("magick: %w", err)
	}

	return out, nil
}

func replaceExt(filename, newExt string) string {
	if i := strings.LastIndex(filename, "."); i >= 0 {
		return filename[:i] + newExt
	}
	return filename + newExt
}