/**
 * Reads and writes the URL based on reveal.js' current state.
 */
export default class Location {
  // The minimum number of milliseconds that must pass between
  // calls to history.replaceState
  MAX_REPLACE_STATE_FREQUENCY = 1000;

  constructor(Reveal) {
    this.Reveal = Reveal;

    // Delays updates to the URL due to a Chrome thumbnailer bug
    this.writeURLTimeout = 0;

    this.replaceStateTimestamp = 0;

    this.onWindowHashChange = this.onWindowHashChange.bind(this);
  }

  bind() {
    window.addEventListener("hashchange", this.onWindowHashChange, false);
  }

  unbind() {
    window.removeEventListener("hashchange", this.onWindowHashChange, false);
  }

  /**
   * Returns the slide indices for the given hash link.
   *
   * @param {string} [hash] the hash string that we want to
   * find the indices for
   *
   * @returns slide indices or null
   */
  getIndicesFromHash(hash = window.location.hash, options = {}) {
    // Attempt to parse the hash as either an index or name
    let name = hash.replace(/^#\/?/, "");
    let bits = name.split("/");

    // If the first bit is not fully numeric and there is a name we
    // can assume that this is a named link
    if (!/^[0-9]*$/.test(bits[0]) && name.length) {
      let element;

      let f;

      // Parse named links with fragments (#/named-link/2)
      if (/\/[-\d]+$/g.test(name)) {
        f = parseInt(name.split("/").pop(), 10);
        f = isNaN(f) ? undefined : f;
        name = name.split("/").shift();
      }

      // Ensure the named link is a valid HTML ID attribute
      try {
        element = document.getElementById(decodeURIComponent(name));
      } catch (error) {}

      if (element) {
        return { ...this.Reveal.getIndices(element), f };
      }
    } else {
      const config = this.Reveal.getConfig();
      let hashIndexBase =
        config.hashOneBasedIndex || options.oneBasedIndex ? 1 : 0;

      // Read the index components of the hash
      let h = parseInt(bits[0], 10) - hashIndexBase || 0,
        v = parseInt(bits[1], 10) - hashIndexBase || 0,
        f;

      if (config.fragmentInURL) {
        f = parseInt(bits[2], 10);
        if (isNaN(f)) {
          f = undefined;
        }
      }

      return { h, v, f };
    }

    // The hash couldn't be parsed or no matching named link was found
    return null;
  }

  /**
   * Reads the current URL (hash) and navigates accordingly.
   */
  readURL() {
    const currentIndices = this.Reveal.getIndices();
    const newIndices = this.getIndicesFromHash();

    if (newIndices) {
      if (
        newIndices.h !== currentIndices.h ||
        newIndices.v !== currentIndices.v ||
        newIndices.f !== undefined
      ) {
        this.Reveal.slide(newIndices.h, newIndices.v, newIndices.f);
      }
    }
    // If no new indices are available, we're trying to navigate to
    // a slide hash that does not exist
    else {
      this.Reveal.slide(currentIndices.h || 0, currentIndices.v || 0);
    }
  }

  /**
   * Updates the page URL (hash) to reflect the current
   * state.
   *
   * @param {number} delay The time in ms to wait before
   * writing the hash
   */
  writeURL(delay) {
    let config = this.Reveal.getConfig();
    let currentSlide = this.Reveal.getCurrentSlide();

    // Make sure there's never more than one timeout running
    clearTimeout(this.writeURLTimeout);

    // If a delay is specified, timeout this call
    if (typeof delay === "number") {
      this.writeURLTimeout = setTimeout(this.writeURL, delay);
    } else if (currentSlide) {
      let hash = this.getHash();

      // If we're configured to push to history OR the history
      // API is not available.
      if (config.history) {
        window.location.hash = hash;
      }
      // If we're configured to reflect the current slide in the
      // URL without pushing to history.
      else if (config.hash) {
        // If the hash is empty, don't add it to the URL
        if (hash === "/") {
          this.debouncedReplaceState(
            window.location.pathname + window.location.search
          );
        } else {
          this.debouncedReplaceState("#" + hash);
        }
      }
      // UPDATE: The below nuking of all hash changes breaks
      // anchors on pages where reveal.js is running. Removed
      // in 4.0. Why was it here in the first place? ¯\_(ツ)_/¯
      //
      // If history and hash are both disabled, a hash may still
      // be added to the URL by clicking on a href with a hash
      // target. Counter this by always removing the hash.
      // else {
      // 	window.history.replaceState( null, null, window.location.pathname + window.location.search );
      // }
    }
  }

  replaceState(url) {
    window.history.replaceState(null, null, url);
    this.replaceStateTimestamp = Date.now();
  }

  debouncedReplaceState(url) {
    clearTimeout(this.replaceStateTimeout);

    if (
      Date.now() - this.replaceStateTimestamp >
      this.MAX_REPLACE_STATE_FREQUENCY
    ) {
      this.replaceState(url);
    } else {
      this.replaceStateTimeout = setTimeout(
        () => this.replaceState(url),
        this.MAX_REPLACE_STATE_FREQUENCY
      );
    }
  }

  /**
   * Return a hash URL that will resolve to the given slide location.
   *
   * @param {HTMLElement} [slide=currentSlide] The slide to link to
   */
  getHash(slide) {
    let url = "/";

    // Attempt to create a named link based on the slide's ID
    let s = slide || this.Reveal.getCurrentSlide();
    let id = s ? s.getAttribute("id") : null;
    if (id) {
      id = encodeURIComponent(id);
    }

    let index = this.Reveal.getIndices(slide);
    if (!this.Reveal.getConfig().fragmentInURL) {
      index.f = undefined;
    }

    // If the current slide has an ID, use that as a named link,
    // but we don't support named links with a fragment index
    if (typeof id === "string" && id.length) {
      url = "/" + id;

      // If there is also a fragment, append that at the end
      // of the named link, like: #/named-link/2
      if (index.f >= 0) url += "/" + index.f;
    }
    // Otherwise use the /h/v index
    else {
      let hashIndexBase = this.Reveal.getConfig().hashOneBasedIndex ? 1 : 0;
      if (index.h > 0 || index.v > 0 || index.f >= 0)
        url += index.h + hashIndexBase;
      if (index.v > 0 || index.f >= 0) url += "/" + (index.v + hashIndexBase);
      if (index.f >= 0) url += "/" + index.f;
    }

    return url;
  }

  /**
   * Handler for the window level 'hashchange' event.
   *
   * @param {object} [event]
   */
  onWindowHashChange(event) {
    this.readURL();
  }
}