import * as jsonld from "jsonld";
import { JsonLd, JsonLdArray } from "jsonld/jsonld-spec";
import { Quad, NamedNode, DataFactory } from "n3";
const { literal, quad, namedNode } = DataFactory;

// const { rdf } = ns;
const rdf = { type: "http://www.w3.org/1999/02/22-rdf-syntax-ns#type" };

function _emitQuad(
  onQuad: (q: Quad) => void,
  subjNode: NamedNode,
  pred: string,
  subj: any,
  graphNode: NamedNode
) {
  let predNode: NamedNode;
  if (pred === "@type") {
    predNode = namedNode(rdf.type);
  } else {
    predNode = namedNode(pred);
  }
  subj[pred as string].forEach(function(obj: any) {
    const objNode = obj["@id"]
      ? namedNode(obj["@id"])
      : literal(obj["@value"], obj["@language"] || obj["@type"]);
    onQuad(quad(subjNode, predNode, objNode, graphNode));
  });
}

export async function eachJsonLdQuad(
  jsonLdObj: object,
  onQuad: (q: Quad) => void
) {
  const expanded = await jsonld.expand(jsonLdObj);

  (expanded as JsonLdArray).forEach(function(g: JsonLd) {
    var graph = (g as { "@id": string })["@id"];
    var graphNode = namedNode(graph);
    (g as { "@graph": JsonLdArray })["@graph"].forEach(function(subj: {
      [predOrId: string]: any;
    }) {
      const subjNode = namedNode(subj["@id"]);
      for (let pred in subj) {
        if (pred === "@id") {
          continue;
        }
        _emitQuad(onQuad, subjNode, pred, subj, graphNode);
      }
    });
  });
}