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import { groupBy } from "https://deno.land/std@0.158.0/collections/group_by.ts";
type Term = {  termType: string,  value: string,  language?: string,  datatype?: Term}
type Quad = {  termType: string,  value: string,  subject: Term,  predicate: Term,  object: Term,  graph: Term,}
type RdfJsonTerm = {  type: 'bnode' | 'uri' | 'literal' | 'defaultgraph',  value: string,  lang?: string,  datatype?: string}
const typeMapping = {  'NamedNode': 'uri',  'Literal': 'literal',  'BlankNode': 'bnode',  'DefaultGraph': 'defaultgraph'} as const
/** * @See https://rdf.js.org/data-model-spec/ * @See https://www.w3.org/TR/rdf-json/#overview-of-rdf-json *  * Maps Quads from the RDF data model spec to application/rdf+json */export const convertQuadsToRdfJson = (quads: Array<Quad>) => {  const root: {    [key: string]: {      [key: string]: Array<RdfJsonTerm>    }  } = {}  const groupedSubjectQuads = groupBy(quads, (item: Quad) => item.subject.value)
  for (const subjectQuads of Object.values(groupedSubjectQuads)) {    if (!subjectQuads) continue    const subject = subjectQuads[0].subject.value
    root[subject] = {}    const groupedPredicatesQuads = groupBy(subjectQuads, (item: Quad) => item.predicate.value)
    for (const predicateQuads of Object.values(groupedPredicatesQuads)) {      if (!predicateQuads) continue            const predicate = predicateQuads[0].predicate.value      root[subject][predicate] = []
      for (const predicateQuad of predicateQuads) {                if (!(predicateQuad.object.termType in typeMapping))           throw new Error('Unexpected termType')
        const type = typeMapping[predicateQuad.object.termType as keyof typeof typeMapping]
        const value: RdfJsonTerm = {          type,          value: predicateQuad.object.value,        }
        if (predicateQuad.object.language) {          value.lang = predicateQuad.object.language        }
        if (predicateQuad.object.datatype) {          value.datatype = predicateQuad.object.datatype.value        }
        root[subject][predicate].push(value)      }    }  }
  return root}