backend: support external SPARQL and named-graph snapshots

backend_go/queryscope/scope.go

@@ -0,0 +1,25 @@
+package queryscope
+
+import "strings"
+
+// NamedGraph wraps a read pattern so app-generated queries read from any named graph via GRAPH ?g.
+func NamedGraph(pattern string) string {
+	trimmed := strings.TrimSpace(pattern)
+	if trimmed == "" {
+		return "  GRAPH ?g {\n  }"
+	}
+
+	return indent("GRAPH ?g {\n"+indent(trimmed, "  ")+"\n}", "  ")
+}
+
+func AskAnyTripleQuery() string {
+	return "ASK WHERE {\n" + NamedGraph("?s ?p ?o .") + "\n}"
+}
+
+func indent(text string, prefix string) string {
+	lines := strings.Split(text, "\n")
+	for i, line := range lines {
+		lines[i] = prefix + line
+	}
+	return strings.Join(lines, "\n")
+}