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import { type Context, fromRdf, Graph, Iri, Node, type RDF } from "./rdf.ts";import type { Property, Schema } from "./schema/mod.ts";import { ldkit, rdf } from "./namespaces/mod.ts";
type DecodedNode = Record<string, unknown>;
class Decoder {  private graph: Graph;  private schema: Schema;  private context: Context;
  private cache: Map<Schema, Map<Iri, DecodedNode>> = new Map();
  private constructor(graph: Graph, schema: Schema, context: Context) {    this.graph = graph;    this.schema = schema;    this.context = context;  }
  static decode(graph: Graph, schema: Schema, context: Context) {    return new Decoder(graph, schema, context).decode();  }
  getCachedNode(nodeIri: Iri, schema: Schema) {    if (!this.cache.has(schema)) {      this.cache.set(schema, new Map());    }    return this.cache.get(schema)!.get(nodeIri);  }
  setCachedNode(nodeIri: Iri, schema: Schema, decodedNode: DecodedNode) {    if (!this.cache.has(schema)) {      this.cache.set(schema, new Map());    }    this.cache.get(schema)!.set(nodeIri, decodedNode);  }
  decode() {    const output: DecodedNode[] = [];
    for (const [iri, properties] of this.graph) {      if (properties.has(rdf.type)) {        const types = properties.get(rdf.type)!;        for (const type of types) {          if (type.termType === "NamedNode" && type.value === ldkit.Resource) {            output.push(this.decodeNode(iri, this.schema));          }        }      }    }
    if (this.graph.size > 0 && output.length < 1) {      throw new Error(        `Unable to decode graph - no resources with type <${ldkit.Resource}> found`,      );    }
    return output;  }
  decodeNode(nodeIri: Iri, schema: Schema) {    const cachedNode = this.getCachedNode(nodeIri, schema);    if (cachedNode) {      return cachedNode;    }
    const output: DecodedNode = {      $id: nodeIri,    };
    const node = this.graph.get(nodeIri);
    if (!node) {      throw new Error(`Error decoding graph, <${nodeIri}> node not found.`);    }
    output.$type = this.decodeNodeType(node);
    Object.keys(schema).forEach((key) => {      if (key === "@type") {        return;      }      const result = this.decodeNodeProperty(        nodeIri,        node,        key,        schema[key] as Property,      );      if (result !== undefined) {        output[key] = result;      }    });
    this.setCachedNode(nodeIri, schema, output);
    return output;  }
  decodeNodeType(node: Node) {    const typeTerms = node.get(rdf.type);    if (!typeTerms) {      return [];    }    return typeTerms.reduce((acc, term) => {      if (term.value !== ldkit.Resource) {        acc.push(term.value);      }      return acc;    }, [] as Iri[]);  }
  decodeNodeProperty(    nodeIri: Iri,    node: Node,    propertyKey: string,    property: Property,  ) {    const terms = node.get(property["@id"]);
    if (!terms) {      if (!property["@optional"]) {        // No data, required property        throw new Error(          `Required property "${propertyKey}" of type <${            property["@id"]          }> not found on resource <${nodeIri}>`,        );      } else {        // No data, optional property        return property["@array"] ? [] : undefined;      }    }
    if (property["@multilang"]) {      if (property["@array"]) {        return terms.reduce((acc, term) => {          if (term.termType !== "Literal") {            throw new Error(              `Property "${propertyKey}" data type mismatch - expected a literal, but received ${term.termType} instead on resource <${nodeIri}>`,            );          }          const language = term.language;          if (!acc[language]) {            acc[language] = [];          }          acc[language].push(this.decodeTerm(term));          return acc;        }, {} as Record<string, string[]>);      } else {        return terms.reduce((acc, term) => {          if (term.termType !== "Literal") {            throw new Error(              `Property "${propertyKey}" data type mismatch - expected a literal, but received ${term.termType} instead on resource <${nodeIri}>`,            );          }          const language = term.language;          if (!acc[language]) {            // If there are multiple strings with the same language detected, selecting only the first one            acc[language] = this.decodeTerm(term);          }          return acc;        }, {} as Record<string, string>);      }    }
    if (property["@array"]) {      if (property["@context"]) {        // Collection of resources specified by sub schema        return terms.map((term) => {          if (term.termType !== "NamedNode" && term.termType !== "BlankNode") {            throw new Error(              `Property "${propertyKey}" data type mismatch - expected a node, but received ${term.termType} instead on resource <${nodeIri}>`,            );          }          return this.decodeNode(term.value, property["@context"]!);        });      } else {        // Collection of literals or named nodes        return terms.map((term) => {          if (term.termType !== "Literal" && term.termType !== "NamedNode") {            throw new Error(              `Property "${propertyKey}" data type mismatch - expected a literal or named node, but received ${term.termType} instead on resource <${nodeIri}>`,            );          }          return this.decodeTerm(term);        });      }    }
    // Single return value expected from this point on    if (property["@context"]) {      for (const term of terms) {        if (term.termType === "NamedNode" || term.termType === "BlankNode") {          return this.decodeNode(term.value, property["@context"]!);        }      }      throw new Error(        `Property "${propertyKey}" data type mismatch - expected a named node for context on resource <${nodeIri}>`,      );    }
    const preferredLanguage = this.context.language;
    if (preferredLanguage) {      // Try to find a term that corresponds to the preferred language      for (const term of terms) {        if (          term.termType === "Literal" &&          term.language === preferredLanguage        ) {          return this.decodeTerm(term);        }      }    }
    // All options exhausted - return first namedNode or literal if there are multiple    for (const term of terms) {      if (term.termType === "Literal" || term.termType === "NamedNode") {        return this.decodeTerm(term);      }    }
    throw new Error(      `Property "${propertyKey}" data type mismatch - expected a literal or named node instead on resource <${nodeIri}>`,    );  }
  decodeTerm(term: RDF.Term) {    if (term.termType === "NamedNode") {      return term.value;    } else if (term.termType === "Literal") {      return fromRdf(term);    } else {      throw new Error(`Unsupported term type to resolve: ${term.termType}`);    }  }}
export const decode = (  graph: Graph,  schema: Schema,  context: Context,) => {  return Decoder.decode(graph, schema, context);};