import { BindingsFactory, type Context, type IQueryEngine, QuadFactory, type RDF, RDFJSON,} from "../rdf.ts";import { ArrayIterator, MappingIterator, TreeIterator,} from "../asynciterator.ts";
type QueryResponseFormat = { "application/sparql-results+json": RDFJSON.SparqlResultsJsonFormat; "application/rdf+json": RDFJSON.RdfJsonFormat;};
export class QueryEngine implements IQueryEngine { protected getSparqlEndpoint(context?: Context) { if (!context) { throw new Error( "No context supplied to QueryEngine. You need to create a default context or pass one to a resource.", ); } if (!Array.isArray(context.sources) || context.sources.length < 1) { throw new Error( "Invalid context `sources` attribute defined. You need to provide a URL to a SPARQL endpoint to query.", ); } if (context.sources.length > 1) { throw new Error( "This query engine supports only one data source, multiple defined in `sources` property in context.", ); } const source = context.sources[0]; if (typeof source === "string") { return source; } if ("value" in source && typeof source.value === "string") { if ("type" in source) { if (source.type === "sparql") { return source.value; } } else { return source.value; } } throw new Error( "Invalid SPARQL source defined - please provide URL to a SPARQL endpoint to query.", ); }
protected getFetch(context?: Context) { return context && context.fetch ? context.fetch : fetch; }
async query< ResponseType extends keyof QueryResponseFormat, ResponseFormat = QueryResponseFormat[ResponseType], >( query: string, responseType: ResponseType, context?: Context, ) { const endpoint = this.getSparqlEndpoint(context); const fetchFn = this.getFetch(context); const response = await fetchFn(endpoint, { method: "POST", headers: { "accept": responseType, "content-type": "application/x-www-form-urlencoded; charset=UTF-8", }, body: new URLSearchParams({ query, }), }); const json = await response.json(); return json as ResponseFormat; }
async queryBindings( query: string, context?: Context, ): Promise<RDF.ResultStream<RDF.Bindings>> { const json = await this.query( query, "application/sparql-results+json", context, );
if (!Array.isArray(json.results?.bindings)) { throw new Error("Bindings SPARQL query result not found"); }
const bindingsFactory = new BindingsFactory();
const bindingsIterator = new ArrayIterator<RDFJSON.Bindings>( json.results!.bindings, );
return new MappingIterator( bindingsIterator, (i) => bindingsFactory.fromJson(i), ) as unknown as RDF.ResultStream<RDF.Bindings>; }
async queryBoolean( query: string, context?: Context, ): Promise<boolean> { const json = await this.query( query, "application/sparql-results+json", context, ); if ("boolean" in json) { return Boolean(json.boolean); } throw new Error("Boolean SPARQL query result not found"); }
async queryQuads( query: string, context?: Context, ): Promise<RDF.ResultStream<RDF.Quad>> { const json = await this.query(query, "application/rdf+json", context);
if (!(json?.constructor === Object)) { throw new Error("Quads SPARQL query result not found"); }
const quadFactory = new QuadFactory();
const treeIterator = new TreeIterator<RDFJSON.Term>(json);
return new MappingIterator( treeIterator, (i) => quadFactory.fromJson(i as [string, string, RDFJSON.Term]), ) as unknown as RDF.ResultStream<RDF.Quad>; }
async queryVoid( query: string, context?: Context, ): Promise<void> { await this.query(query, "application/sparql-results+json", context); }}