let mainfig: HTMLElement;
let mainimg: HTMLImageElement;
let mainlink: HTMLAnchorElement;
let altButtons: HTMLInputElement[];
let skipAll: HTMLInputElement;

const opened: Set<string> = new Set;

function openCW(id: string | null, caption: HTMLElement, focusLink = false): void {
  if (id !== null) opened.add(id);
  if (caption.parentElement) {
    mainfig.removeChild(caption);
  }
  mainlink.tabIndex = 0;
  if (focusLink) mainlink.focus();
}

function addCWListeners(id: string | null, caption: HTMLElement): void {
  caption.addEventListener('click', _e => openCW(id, caption));
  caption.addEventListener('keyup',
    e => { if (e.key == 'Enter') openCW(id, caption, true) });
}

function setImage(id: string, src: string, href: string,
                  alt: string, cw: string): void {
  const curCw = document.getElementById('cw');
  const coverNew = cw != '' && !opened.has(id) && !skipAll.checked;

  if (curCw && !coverNew) {
    // keep old cover until load
    function removeCover() { setTimeout(() => openCW(null, curCw!), 100); }
    mainimg.addEventListener('load', removeCover, {once: true});
  } else if (coverNew) {
    // place new cover
    const newCw =
      (document.getElementById('cw-template') as HTMLTemplateElement)
        .content.firstElementChild!.cloneNode(true) as HTMLElement;
    newCw.querySelector('#cw-text')!.innerHTML = cw;

    if (curCw) openCW(null, curCw);
    mainfig.insertBefore(newCw, mainlink);
    mainlink.tabIndex = -1;

    addCWListeners(id, newCw);
  }
  // else no cover before or after

  mainimg.src = src;
  mainimg.alt = mainimg.title = alt;
  mainlink.href = href;
}

function activateButton(button: HTMLInputElement, doPush = true): void {
  setImage(button.id, button.value,
           button.dataset.link!,
           button.dataset.alt ?? '',
           button.dataset.warning ?? '');

  if (doPush) history.pushState(null, '', '#' + button.id);
}

function useFragment(firstLoad = false): void {
  let button = altButtons[0];

  const frag = decodeURIComponent(location.hash).replace(/^#/, '');
  if (frag) {
    const selected = document.getElementById(frag) as HTMLInputElement;
    if (selected) button = selected;
  }

  let id: string | null = null;

  if (button) {
    id = button.id;
    button.checked = true;
    activateButton(button, false);
  }

  if (firstLoad) {
    const cw = document.getElementById('cw');
    if (cw) addCWListeners(id, cw);
  }
}

function setup() {
  mainfig  = document.getElementById('mainfig')!;
  mainimg  = document.getElementById('mainimg') as HTMLImageElement;
  mainlink = document.getElementById('mainlink') as HTMLAnchorElement;
  skipAll  = document.getElementById('skipAll') as HTMLInputElement;

  const alts = document.getElementById('alts');
  if (alts) {
    const inputs = Array.from(alts.getElementsByTagName('input'));
    altButtons = inputs.filter(e => e.name == 'variant');
  } else {
    altButtons = [];
  }

  for (const button of altButtons) {
    button.onchange = _e => { if (button.checked) activateButton(button); };
  }

  if (skipAll) {
    skipAll.onchange = _e => { if (skipAll.checked) {
      const caption = document.getElementById('cw');
      if (caption) { openCW(null, caption, false); }
    } };
  }

  window.addEventListener('popstate', _e => useFragment());
  useFragment(true);
}

window.addEventListener('DOMContentLoaded', setup);

export {};