// gestures.js — 触控手势检测器（简化版）
//
// 仅支持 6 种手势：单击 · 双击 · 左滑 · 右滑 · 上滑 · 下滑
// 无长按，无多指操作

class GestureDetector {
  constructor(el) {
    this._el = el;
    this._handlers = {};

    this._startX = 0;
    this._startY = 0;
    this._startTime = 0;
    this._tapTimer = null;
    this._tapCount = 0;

    this._bindTouch();
    this._bindMouse();
    this._bindKeyboard();
  }

  on(evt, fn) { this._handlers[evt] = fn; return this; }

  _emit(evt) {
    dbg(evt);
    const fn = this._handlers[evt];
    if (fn) fn();
  }

  // ── 触摸事件 ──
  _bindTouch() {
    const el = this._el;
    el.addEventListener('touchstart', e => {
      e.preventDefault();
      const t = e.touches[0];
      this._startX = t.clientX;
      this._startY = t.clientY;
      this._startTime = Date.now();
    }, { passive: false });

    el.addEventListener('touchend', e => {
      e.preventDefault();
      const t = e.changedTouches[0];
      this._process(t.clientX, t.clientY);
    }, { passive: false });

    el.addEventListener('touchcancel', () => this._reset(), { passive: false });
  }

  // ── 鼠标事件（桌面调试）──
  _bindMouse() {
    this._el.addEventListener('mousedown', e => {
      this._startX = e.clientX;
      this._startY = e.clientY;
      this._startTime = Date.now();
    });
    this._el.addEventListener('mouseup', e => {
      this._process(e.clientX, e.clientY);
    });
  }

  // ── 键盘事件（桌面调试）──
  _bindKeyboard() {
    document.addEventListener('keydown', e => {
      switch (e.code) {
        case 'Space':      e.preventDefault(); this._emit('singletap'); break;
        case 'Enter':      e.preventDefault(); this._emit('doubletap'); break;
        case 'ArrowLeft':  e.preventDefault(); this._emit('swipe_left'); break;
        case 'ArrowRight': e.preventDefault(); this._emit('swipe_right'); break;
        case 'ArrowUp':    e.preventDefault(); this._emit('swipe_up'); break;
        case 'ArrowDown':  e.preventDefault(); this._emit('swipe_down'); break;
      }
    });
  }

  // ── 手势判定 ──
  _process(endX, endY) {
    const dx = endX - this._startX;
    const dy = endY - this._startY;
    const dist = Math.sqrt(dx * dx + dy * dy);
    const dt = Date.now() - this._startTime;

    // 滑动：距离 > 35px
    if (dist > 35) {
      const angle = Math.abs(Math.atan2(dy, dx) * 180 / Math.PI);
      let dir = null;

      if (angle < 45)           dir = 'right';
      else if (angle > 135)     dir = 'left';
      else if (dy < 0 && Math.abs(dy) > Math.abs(dx)) dir = 'up';
      else if (dy > 0 && Math.abs(dy) > Math.abs(dx)) dir = 'down';

      if (dir) {
        this._tapCount = 0;
        clearTimeout(this._tapTimer);
        this._emit(`swipe_${dir}`);
        return;
      }
    }

    // 点击：距离 < 20px，时间 < 500ms
    if (dist < 20 && dt < 500) {
      this._tapCount++;
      if (this._tapCount === 1) {
        this._tapTimer = setTimeout(() => {
          this._tapCount = 0;
          this._emit('singletap');
        }, 250);
      } else if (this._tapCount >= 2) {
        clearTimeout(this._tapTimer);
        this._tapCount = 0;
        this._emit('doubletap');
      }
    }
  }

  _reset() {
    clearTimeout(this._tapTimer);
    this._tapCount = 0;
  }
}