import { Document, Element, parseXml } from 'libxmljs';
import { VError } from 'verror';

export class XMLReader {
  private document: Document;
  private namespaces: Record<string, string>;

  constructor(inputXml: string) {
    try {
      this.document = parseXml(inputXml);
      this.namespaces = {};

      // Bad typings? No .namespaces()
      for (const ns of (this.document as any).namespaces()) {
        let name = ns.prefix();
        if (name === null) {
          name = '_';
        }
        this.namespaces[name] = ns.href();
      }
    } catch (cause) {
      throw new VError(
        { cause, name: 'ParseError', info: { inputXml } },
        'Failed to parse XML',
      );
    }
  }

  public get(xpath: string): string {
    const element: Element | null = this.document.get(xpath, this.namespaces);

    if (element === null || element === undefined) {
      throw new Error(`XPath element "${xpath}" was not found`);
    }

    return element.text();
  }
}

const input: string = `<?xml version="1.0" encoding="UTF-8"?>
  <root xmlns="default:namespace" xmlns:opt="inner:namespace">
    <outer><opt:inner>value</opt:inner></outer>
  </root>
  `;

const xml = new XMLReader(input);

// Need to specify the default namespace with _.
console.log(xml.get('/_:root/_:outer/opt:inner'));