package catalog

import (
	"encoding/hex"
	"fmt"
	"strings"
)

func (c *CatalogImage) SHA256() (string, error) {
	if c.Checksum == "" {
		return "", fmt.Errorf("checksum is empty")
	}

	const prefix = "sha256:"
	if !strings.HasPrefix(c.Checksum, prefix) {
		return "", fmt.Errorf("unsupported checksum format (expected sha256:...)")
	}

	hash := strings.TrimPrefix(c.Checksum, prefix)

	if len(hash) != 64 {
		return "", fmt.Errorf("invalid sha256 length: got %d, want 64", len(hash))
	}

	if _, err := hex.DecodeString(hash); err != nil {
		return "", fmt.Errorf("invalid sha256 hex: %w", err)
	}

	return hash, nil
}