import { Store, Term, NamedNode } from "n3";
import { RDFS } from "./namespaces";

function _singleValue(g: Store, s: Term, p: Term): Term {
  const quads = g.getQuads(s, p, null, null);
  const objs = new Set(quads.map((q) => q.object));
  if (objs.size == 0) {
    throw new Error("no value for " + s.value + " " + p.value);
  } else if (objs.size == 1) {
    const obj = objs.values().next().value;
    return obj as Term;
  } else {
    throw new Error("too many different values: " + JSON.stringify(quads));
  }
}

export function stringValue(g: Store, s: Term, p: Term): string {
  const ret = _singleValue(g, s, p);
  if (ret.termType != "Literal") {
    throw new Error(`ret=${ret}`);
  }
  return ret.value as string;
}

export function uriValue(g: Store, s: Term, p: Term): NamedNode {
  const ret = _singleValue(g, s, p);
  if (ret.termType != "NamedNode") {
    throw new Error(`ret=${ret}`);
  }

  return ret;
}

export function labelOrTail(g: Store, uri: NamedNode): string {
  let ret: string;
  try {
    ret = stringValue(g, uri, RDFS("label"));
  } catch (e) {
    const words = uri.value.split("/");
    ret = words[words.length - 1];
  }
  if (!ret) {
    ret = uri.value;
  }
  return ret;
}