/**
 * Tauri WebView — HTML5 DnD 대신 pointer capture 기반 팔레트 드래그
 */
import { clientXYFromNative } from './pointerDrag';
import { isDesktop } from './platform';

export type PaletteDragPayload = Record<string, unknown> & {
  type: string;
  value: string;
  label: string;
};

export type PaletteDragPhase = 'start' | 'move' | 'end' | 'cancel';

export interface PaletteDragEvent {
  phase: PaletteDragPhase;
  x: number;
  y: number;
  payload: PaletteDragPayload;
}

type PaletteDragListener = (event: PaletteDragEvent) => void;
type PaletteDropHandler = (event: PaletteDragEvent) => void;

let suppressClickUntil = 0;
const DRAG_THRESHOLD_PX = 6;

let activePayload: PaletteDragPayload | null = null;
let activePointerId: number | null = null;
let unbindMove: (() => void) | null = null;
let pendingPointerId: number | null = null;
let listeners = new Set<PaletteDragListener>();
let dropHandler: PaletteDropHandler | null = null;

export function needsPointerPaletteDrag(): boolean {
  return isDesktop();
}

export function subscribePaletteDrag(listener: PaletteDragListener): () => void {
  listeners.add(listener);
  return () => listeners.delete(listener);
}

/** Canvas 가 mount 직후 drop 콜백 등록 (subscribe 누락 방지) */
export function setPaletteDragDropHandler(handler: PaletteDropHandler | null): void {
  dropHandler = handler;
}

export function getActivePaletteDrag(): PaletteDragPayload | null {
  return activePayload;
}

export function shouldSuppressPaletteClick(): boolean {
  return Date.now() < suppressClickUntil;
}

function emit(event: PaletteDragEvent) {
  listeners.forEach(fn => {
    try {
      fn(event);
    } catch {
      /* ignore */
    }
  });
}

function dispatchEnd(xy: { x: number; y: number }, payload: PaletteDragPayload) {
  const event: PaletteDragEvent = { phase: 'end', x: xy.x, y: xy.y, payload };
  dropHandler?.(event);
  emit(event);
}

function cleanupDrag() {
  unbindMove?.();
  unbindMove = null;
  activePayload = null;
  activePointerId = null;
  pendingPointerId = null;
  document.body.classList.remove('se-palette-drag-active');
  document.querySelectorAll('.se-palette-drag-ghost').forEach(el => el.remove());
}

function finishDrag(phase: 'end' | 'cancel', xy: { x: number; y: number }) {
  if (!activePayload) return;
  const payload = activePayload;
  cleanupDrag();
  if (phase === 'end') {
    suppressClickUntil = Date.now() + 400;
    dispatchEnd(xy, payload);
  } else {
    emit({ phase: 'cancel', x: xy.x, y: xy.y, payload });
  }
}

/** 캔버스 pointerup 백업 — WebView 에서 window 이벤트 누락 시 */
export function completePaletteDragAt(clientX: number, clientY: number): boolean {
  if (!activePayload) return false;
  finishDrag('end', { x: clientX, y: clientY });
  return true;
}

function beginDrag(
  payload: PaletteDragPayload,
  xy: { x: number; y: number },
  pointerId: number,
) {
  activePayload = payload;
  activePointerId = pointerId;
  document.body.classList.add('se-palette-drag-active');

  try {
    document.body.setPointerCapture(pointerId);
  } catch {
    /* ignore */
  }

  emit({ phase: 'start', x: xy.x, y: xy.y, payload });

  const onMove = (ev: Event) => {
    if (!(ev instanceof PointerEvent) || ev.pointerId !== pointerId || !activePayload) return;
    if (ev.cancelable) ev.preventDefault();
    emit({ phase: 'move', x: ev.clientX, y: ev.clientY, payload: activePayload });
  };

  const onUp = (ev: Event) => {
    if (!(ev instanceof PointerEvent) || ev.pointerId !== pointerId) return;
    const xy = clientXYFromNative(ev) ?? { x: ev.clientX, y: ev.clientY };
    finishDrag('end', xy);
  };

  window.addEventListener('pointermove', onMove, { passive: false });
  window.addEventListener('pointerup', onUp, true);
  window.addEventListener('pointercancel', onUp, true);
  window.addEventListener('mouseup', onUp, true);
  document.addEventListener('pointerup', onUp, true);
  document.addEventListener('lostpointercapture', onUp, true);

  unbindMove = () => {
    window.removeEventListener('pointermove', onMove);
    window.removeEventListener('pointerup', onUp, true);
    window.removeEventListener('pointercancel', onUp, true);
    window.removeEventListener('mouseup', onUp, true);
    document.removeEventListener('pointerup', onUp, true);
    document.removeEventListener('lostpointercapture', onUp, true);
    try {
      if (document.body.hasPointerCapture(pointerId)) {
        document.body.releasePointerCapture(pointerId);
      }
    } catch {
      /* ignore */
    }
  };
}

export function handlePalettePointerDown(
  e: React.PointerEvent,
  payload: PaletteDragPayload,
  _label: string,
): void {
  if (!needsPointerPaletteDrag()) return;
  if (e.button !== 0) return;
  if ((e.target as HTMLElement).closest('input, textarea, select, button')) return;

  const startX = e.clientX;
  const startY = e.clientY;
  const pointerId = e.pointerId;
  pendingPointerId = pointerId;

  const onPointerMove = (ev: PointerEvent) => {
    if (ev.pointerId !== pointerId) return;
    const dx = ev.clientX - startX;
    const dy = ev.clientY - startY;
    if (Math.hypot(dx, dy) < DRAG_THRESHOLD_PX) return;

    window.removeEventListener('pointermove', onPointerMove);
    window.removeEventListener('pointerup', onPointerUp);
    window.removeEventListener('pointercancel', onPointerCancel);

    ev.preventDefault();
    beginDrag(payload, { x: ev.clientX, y: ev.clientY }, pointerId);
  };

  const onPointerUp = (ev: PointerEvent) => {
    if (ev.pointerId !== pointerId) return;
    window.removeEventListener('pointermove', onPointerMove);
    window.removeEventListener('pointerup', onPointerUp);
    window.removeEventListener('pointercancel', onPointerCancel);
    pendingPointerId = null;
  };

  const onPointerCancel = onPointerUp;

  window.addEventListener('pointermove', onPointerMove);
  window.addEventListener('pointerup', onPointerUp);
  window.addEventListener('pointercancel', onPointerCancel);
}

export function writePaletteHtmlDragData(e: React.DragEvent, payload: PaletteDragPayload): void {
  const json = JSON.stringify(payload);
  e.dataTransfer.setData('application/json', json);
  e.dataTransfer.setData('text/plain', json);
  e.dataTransfer.effectAllowed = 'copy';
}

export function isPaletteHtmlDrag(e: React.DragEvent): boolean {
  return e.dataTransfer.types.includes('application/json')
    || e.dataTransfer.types.includes('text/plain');
}

export function readPaletteHtmlDragData(e: React.DragEvent): PaletteDragPayload | null {
  const raw = e.dataTransfer.getData('application/json')
    || e.dataTransfer.getData('text/plain');
  if (!raw) return null;
  try {
    return JSON.parse(raw) as PaletteDragPayload;
  } catch {
    return null;
  }
}

export function findPaletteDropKeyAtPoint(x: number, y: number): string | null {
  const el = document.elementFromPoint(x, y);
  if (!el) return null;
  const host = el.closest('[data-palette-drop-key]') as HTMLElement | null;
  return host?.dataset.paletteDropKey ?? null;
}