Add BuildURLs helper

internal/core/client.go

@@ -245,3 +245,22 @@ func (b *BaseURLs) PURL(name, version string) string {
 	}
 	return fmt.Sprintf("pkg:%s/%s", "generic", name)
 }
+
+// BuildURLs returns a map of all non-empty URLs for a package.
+// Keys are "registry", "download", "docs", and "purl".
+func BuildURLs(urls URLBuilder, name, version string) map[string]string {
+	result := make(map[string]string)
+	if v := urls.Registry(name, version); v != "" {
+		result["registry"] = v
+	}
+	if v := urls.Download(name, version); v != "" {
+		result["download"] = v
+	}
+	if v := urls.Documentation(name, version); v != "" {
+		result["docs"] = v
+	}
+	if v := urls.PURL(name, version); v != "" {
+		result["purl"] = v
+	}
+	return result
+}

internal/core/client_test.go

@@ -7,6 +7,57 @@ import (
 	"testing"
 )
 
+func TestBuildURLs(t *testing.T) {
+	urls := &BaseURLs{
+		RegistryFn:      func(name, version string) string { return "https://example.com/" + name },
+		DownloadFn:      func(name, version string) string { return "https://example.com/" + name + "/download" },
+		DocumentationFn: func(name, version string) string { return "https://docs.example.com/" + name },
+		PURLFn:          func(name, version string) string { return "pkg:test/" + name + "@" + version },
+	}
+
+	got := BuildURLs(urls, "foo", "1.0.0")
+
+	expected := map[string]string{
+		"registry": "https://example.com/foo",
+		"download": "https://example.com/foo/download",
+		"docs":     "https://docs.example.com/foo",
+		"purl":     "pkg:test/foo@1.0.0",
+	}
+
+	if len(got) != len(expected) {
+		t.Fatalf("BuildURLs returned %d entries, want %d", len(got), len(expected))
+	}
+
+	for k, want := range expected {
+		if got[k] != want {
+			t.Errorf("BuildURLs[%q] = %q, want %q", k, got[k], want)
+		}
+	}
+}
+
+func TestBuildURLs_OmitsEmpty(t *testing.T) {
+	urls := &BaseURLs{
+		RegistryFn: func(name, version string) string { return "https://example.com/" + name },
+		// Documentation and Download are nil, so they return ""
+	}
+
+	got := BuildURLs(urls, "foo", "1.0.0")
+
+	if _, ok := got["docs"]; ok {
+		t.Error("BuildURLs should omit empty docs URL")
+	}
+	if _, ok := got["download"]; ok {
+		t.Error("BuildURLs should omit empty download URL")
+	}
+	if _, ok := got["registry"]; !ok {
+		t.Error("BuildURLs should include non-empty registry URL")
+	}
+	// PURL falls back to generic format in BaseURLs
+	if _, ok := got["purl"]; !ok {
+		t.Error("BuildURLs should include PURL fallback")
+	}
+}
+
 func TestDefaultClient_UserAgent(t *testing.T) {
 	var gotUA string
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {

registries.go

@@ -135,6 +135,12 @@ func SupportedEcosystems() []string {
 	return core.SupportedEcosystems()
 }
 
+// BuildURLs returns a map of all non-empty URLs for a package.
+// Keys are "registry", "download", "docs", and "purl".
+func BuildURLs(urls URLBuilder, name, version string) map[string]string {
+	return core.BuildURLs(urls, name, version)
+}
+
 // DefaultURL returns the default registry URL for an ecosystem.
 func DefaultURL(ecosystem string) string {
 	return core.DefaultURL(ecosystem)

registries_test.go

@@ -174,6 +174,25 @@ func TestIntegration(t *testing.T) {
 	}
 }
 
+func TestBuildURLs(t *testing.T) {
+	reg, err := registries.New("cargo", "", nil)
+	if err != nil {
+		t.Fatalf("New failed: %v", err)
+	}
+
+	got := registries.BuildURLs(reg.URLs(), "serde", "1.0.0")
+
+	if got["registry"] == "" {
+		t.Error("expected non-empty registry URL")
+	}
+	if got["docs"] == "" {
+		t.Error("expected non-empty docs URL")
+	}
+	if got["purl"] != "pkg:cargo/serde@1.0.0" {
+		t.Errorf("purl = %q, want %q", got["purl"], "pkg:cargo/serde@1.0.0")
+	}
+}
+
 func TestConstants(t *testing.T) {
 	// Verify constants are exported correctly
 	if registries.Runtime != "runtime" {