Vim-Vixen/src/content/presenters/NavigationPresenter.ts

export default interface NavigationPresenter {
  openHistoryPrev(): void;

  openHistoryNext(): void;

  openLinkPrev(): void;

  openLinkNext(): void;
}

const REL_PATTERN: {[key: string]: RegExp} = {
  prev: /^(?:prev(?:ious)?|older)\b|\u2039|\u2190|\xab|\u226a|<</i,
  next: /^(?:next|newer)\b|\u203a|\u2192|\xbb|\u226b|>>/i,
};

// Return the last element in the document matching the supplied selector
// and the optional filter, or null if there are no matches.
// eslint-disable-next-line func-style
function selectLast<E extends Element>(
  selector: string,
  filter?: (e: E) => boolean,
): E | null {
  let nodes = Array.from(
    window.document.querySelectorAll(selector) as NodeListOf<E>
  );

  if (filter) {
    nodes = nodes.filter(filter);
  }
  return nodes.length ? nodes[nodes.length - 1] : null;
}

export class NavigationPresenterImpl implements NavigationPresenter {
  openHistoryPrev(): void {
    window.history.back();
  }

  openHistoryNext(): void {
    window.history.forward();
  }

  openLinkPrev(): void {
    this.linkRel('prev');
  }

  openLinkNext(): void {
    this.linkRel('next');
  }

  // Code common to linkPrev and linkNext which navigates to the specified page.
  private linkRel(rel: 'prev' | 'next'): void {
    let link = selectLast<HTMLLinkElement>(`link[rel~=${rel}][href]`);
    if (link) {
      window.location.href = link.href;
      return;
    }

    const pattern = REL_PATTERN[rel];

    let a = selectLast<HTMLAnchorElement>(`a[rel~=${rel}][href]`) ||
    // `innerText` is much slower than `textContent`, but produces much better
    // (i.e. less unexpected) results
    selectLast('a[href]', lnk => pattern.test(lnk.innerText));

    if (a) {
      a.click();
    }
  }
}