/** @module gpx */
/// <reference path="result.js" />

/**
 * @typedef {[String, String, String]} Segment
 * A tuple of latitude, longtitude and time.
 */

import { parseXml } from "@rgrove/parse-xml";
import { ERROR, OK } from "./result.js";

/**
 * Checks if the given JSON object is an element. Utility function for working
 * with JsonObject converted from XML.
 *
 * @param {JsonObject} object object to check.
 * @returns {boolean} True if the object.type is an element, false otherwise.
 */
const isElement = (object) => object?.type === "element";

/**
 * Checks if the given JSON object is an GPS track object.
 * Utility function for working with JsonObject converted from XML.
 *
 * @param {JsonObject} object to check.
 * @returns {boolean} True if the object.name is trk, false otherwise.
 */
const isTrack = (object) => object?.name === "trk";

/**
 * Checks if the given JSON object is an GPS track segment object.
 * Utility function for working with JsonObject converted from XML.
 *
 * @param {JsonObject} object to check.
 * @returns {boolean} True if the object.name is trkseg, false otherwise.
 */
const isTrackSegment = (object) => object?.name === "trkseg";

/**
 * Checks if the given JSON object is an GPS track segment time object.
 * Utility function for working with JsonObject converted from XML.
 *
 * @param {JsonObject} object to check.
 * @returns {boolean} True if the object.name is time, false otherwise.
 */
const isSegmentTime = (object) => object?.name === "time";

/**
 * Checks if the given JSON object have all nesessary data.
 * Utility function for working with JsonObject converted from XML.
 *
 * @param {JsonObject} object to check.
 * @returns {boolean} True if the object have latitude longtitude and time.
 */
const isProperSegment = (object) => {
  const haveLat = object?.attributes?.lat !== undefined;
  const haveLon = object?.attributes?.lon !== undefined;
  const children = object?.children ?? [];
  const timeObject = children.filter(isSegmentTime)?.[0];
  const haveTime =
    timeObject !== undefined && timeObject.children[0].text.length > 0;

  return haveLat && haveLon && haveTime;
};

/**
 * Take longtitude, latitude and time from JSON object
 * and return it as Segment tuple.
 *
 * @param {JsonObject} object to check.
 * @returns {Segment} True if the object have latitude longtitude and time.
 */
const getSegmentData = (object) => {
  const segmentTime = object.children.filter(isSegmentTime)[0].children[0].text;
  return [object.attributes.lat, object.attributes.lon, segmentTime];
};

/**
 * Parse XML document, turn it into JSON and find track segments,
 * then transform every object to Segment tuple
 *
 * @param {String} xmlDoc string representation of XML document.
 * @returns {Result<[Segment]>}
 */
function parse(xmlDoc) {
  // Check input argument
  if (!xmlDoc || xmlDoc.length === 0) {
    return [ERROR, "Can not parse empty document"];
  }

  const gpxObject = parseXml(xmlDoc);
  const root = gpxObject.toJSON().children?.[0];

  if (!root) {
    return [ERROR, "Document doesn't contain root element"];
  }

  const track = root.children.filter(isElement).filter(isTrack)?.[0];

  if (!track) {
    return [ERROR, "Document doesn't contain track element"];
  }

  const segments = track.children
    .filter(isElement)
    .filter(isTrackSegment)
    .reduce(
      (seg1, seg2) => [...(seg1?.children ?? []), ...(seg2?.children ?? [])],
      [],
    )
    .filter(isElement)
    .filter(isProperSegment)
    .map(getSegmentData);

  if (segments.length === 0) {
    return [ERROR, "There are no track segments to process"];
  }

  return [OK, segments];
}

export { parse };