// Header segmented control: "График" / "Карта" / "Карта и график" plus the
// draggable vertical splitter used in the combined mode. State (mode + split
// ratio) persists in localStorage.
export type ViewMode = 'timeline' | 'map' | 'split';

const LS_MODE = 'mapdash.viewmode';
const LS_SPLIT = 'mapdash.splitLeft';
const MIN_PCT = 20;
const MAX_PCT = 80;

export interface ViewModeElements {
  view: HTMLElement;
  splitResizer: HTMLElement;
  btnTimeline: HTMLElement;
  btnMap: HTMLElement;
  btnSplit: HTMLElement;
}

export interface ViewModeController {
  getMode(): ViewMode;
  setMode(mode: ViewMode): void;
}

export interface ViewModeCallbacks {
  // Called after the mode changes (layout already applied). mapVisible/timelineVisible
  // tell the caller what to (re)initialise or resize.
  onChange(mode: ViewMode): void;
  // Called continuously while the splitter is dragged (rAF-throttled).
  onResize(): void;
}

export function createViewModes(els: ViewModeElements, cb: ViewModeCallbacks): ViewModeController {
  let mode: ViewMode = 'timeline';

  const savedSplit = parseFloat(localStorage.getItem(LS_SPLIT) || '');
  if (savedSplit >= MIN_PCT && savedSplit <= MAX_PCT) {
    els.view.style.setProperty('--split-left', savedSplit + '%');
  }

  function positionIndicator(): void {
    const active = mode === 'timeline' ? els.btnTimeline : mode === 'map' ? els.btnMap : els.btnSplit;
    const ind = els.btnTimeline.parentElement?.querySelector<HTMLElement>('.mode-ind');
    if (ind && active.offsetHeight) {
      ind.style.top = active.offsetTop + 'px';
      ind.style.height = active.offsetHeight + 'px';
    }
  }
  function apply(): void {
    els.view.classList.remove('mode-timeline', 'mode-map', 'mode-split');
    els.view.classList.add('mode-' + mode);
    els.btnTimeline.classList.toggle('active', mode === 'timeline');
    els.btnMap.classList.toggle('active', mode === 'map');
    els.btnSplit.classList.toggle('active', mode === 'split');
    positionIndicator();
  }
  window.addEventListener('resize', positionIndicator);

  function setMode(next: ViewMode): void {
    mode = next;
    localStorage.setItem(LS_MODE, mode);
    apply();
    cb.onChange(mode);
  }

  els.btnTimeline.addEventListener('click', () => setMode('timeline'));
  els.btnMap.addEventListener('click', () => setMode('map'));
  els.btnSplit.addEventListener('click', () => setMode('split'));

  // ---- splitter drag ----
  let dragging = false;
  let rafPending = false;
  let lastPct = savedSplit >= MIN_PCT ? savedSplit : 50;
  function applyDrag(): void {
    rafPending = false;
    els.view.style.setProperty('--split-left', lastPct + '%');
    cb.onResize();
  }
  els.splitResizer.addEventListener('mousedown', (e) => {
    if (mode !== 'split') return;
    dragging = true;
    document.body.style.userSelect = 'none';
    document.body.style.cursor = 'col-resize';
    e.preventDefault();
  });
  window.addEventListener('mousemove', (e) => {
    if (!dragging) return;
    const rect = els.view.getBoundingClientRect();
    let pct = ((e.clientX - rect.left) / rect.width) * 100;
    pct = Math.max(MIN_PCT, Math.min(MAX_PCT, pct));
    lastPct = pct;
    if (rafPending) return;
    rafPending = true;
    requestAnimationFrame(applyDrag);
  });
  window.addEventListener('mouseup', () => {
    if (!dragging) return;
    dragging = false;
    document.body.style.userSelect = '';
    document.body.style.cursor = '';
    localStorage.setItem(LS_SPLIT, String(lastPct));
    cb.onResize();
  });

  // initial mode from storage
  const saved = localStorage.getItem(LS_MODE) as ViewMode | null;
  mode = saved === 'map' || saved === 'split' ? saved : 'timeline';
  apply();
  requestAnimationFrame(positionIndicator); // header is laid out by the next frame

  return {
    getMode: () => mode,
    setMode,
  };
}