// gestures.js — 触控手势检测器
//
// 支持 9 种手势：
//   单击 · 双击 · 长按(1s) · 左滑 · 右滑 · 上滑 · 下滑
//   两指长按(1s) · 三指点击

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

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

    // 长按检测
    this._longPressTimer = null;
    this._longPressTriggered = false;

    // 多指检测
    this._maxTouches = 0;          // 本次触摸中同时出现的最大手指数
    this._multiTouchLPTimer = null; // 两指长按计时器
    this._multiTouchHandled = false;

    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 count = e.touches.length;

      // 记录本次触摸出现过的最大手指数
      if (count > this._maxTouches) this._maxTouches = count;

      if (count === 1) {
        // 单指：记录起点 + 启动长按计时
        const t = e.touches[0];
        this._startX = t.clientX;
        this._startY = t.clientY;
        this._startTime = Date.now();
        this._longPressTriggered = false;

        this._longPressTimer = setTimeout(() => {
          this._longPressTriggered = true;
          this._longPressTimer = null;
          this._emit('longpress');
        }, 1000);

      } else if (count === 2) {
        // 两指：取消单指长按，启动两指长按计时
        this._cancelLongPress();
        this._multiTouchLPTimer = setTimeout(() => {
          this._multiTouchHandled = true;
          this._multiTouchLPTimer = null;
          this._emit('twofinger_longpress');
        }, 1000);

      } else if (count >= 3) {
        // 三指+：取消所有计时
        this._cancelLongPress();
        this._cancelMultiTouchLP();
      }
    }, { passive: false });

    el.addEventListener('touchmove', e => {
      e.preventDefault();
      // 移动超 15px 取消长按
      if (this._longPressTimer && e.touches.length === 1) {
        const t = e.touches[0];
        const dx = t.clientX - this._startX;
        const dy = t.clientY - this._startY;
        if (Math.sqrt(dx * dx + dy * dy) > 15) {
          this._cancelLongPress();
        }
      }
      // 两指移动也取消两指长按
      if (this._multiTouchLPTimer) {
        this._cancelMultiTouchLP();
      }
    }, { passive: false });

    el.addEventListener('touchend', e => {
      e.preventDefault();

      // 还有手指在屏幕上，等全部抬起再处理
      if (e.touches.length > 0) return;

      // 全部手指抬起 — 根据 maxTouches 判定手势类型
      const max = this._maxTouches;

      // 清理计时器
      this._cancelLongPress();
      this._cancelMultiTouchLP();

      // 已在计时器中处理过（长按 / 两指长按）
      if (this._longPressTriggered || this._multiTouchHandled) {
        this._resetMultiTouch();
        return;
      }

      // 三指点击
      if (max >= 3) {
        this._resetMultiTouch();
        this._emit('threefinger_tap');
        return;
      }

      // 两指快速触摸（< 1s）→ 忽略
      if (max === 2) {
        this._resetMultiTouch();
        return;
      }

      // 单指：正常处理（滑动 / 点击）
      this._resetMultiTouch();
      const t = e.changedTouches[0];
      this._process(t.clientX, t.clientY);
    }, { passive: false });

    el.addEventListener('touchcancel', () => {
      this._cancelLongPress();
      this._cancelMultiTouchLP();
      this._resetMultiTouch();
      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._longPressTriggered = false;

      this._longPressTimer = setTimeout(() => {
        this._longPressTriggered = true;
        this._longPressTimer = null;
        this._emit('longpress');
      }, 1000);
    });
    this._el.addEventListener('mouseup', e => {
      this._cancelLongPress();
      if (this._longPressTriggered) {
        this._longPressTriggered = false;
        return;
      }
      this._process(e.clientX, e.clientY);
    });
    this._el.addEventListener('mousemove', e => {
      if (this._longPressTimer) {
        const dx = e.clientX - this._startX;
        const dy = e.clientY - this._startY;
        if (Math.sqrt(dx * dx + dy * dy) > 15) {
          this._cancelLongPress();
        }
      }
    });
  }

  // ── 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;
        case 'KeyL':       e.preventDefault(); this._emit('longpress'); break;
        case 'KeyP':       e.preventDefault(); this._emit('twofinger_longpress'); break;
        case 'KeyQ':       e.preventDefault(); this._emit('threefinger_tap'); break;
      }
    });
  }

  // ── 手势判定（单指） ──
  _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');
      }
    }
  }

  // ── 工具方法 ──

  _cancelLongPress() {
    if (this._longPressTimer) {
      clearTimeout(this._longPressTimer);
      this._longPressTimer = null;
    }
  }

  _cancelMultiTouchLP() {
    if (this._multiTouchLPTimer) {
      clearTimeout(this._multiTouchLPTimer);
      this._multiTouchLPTimer = null;
    }
  }

  _resetMultiTouch() {
    this._maxTouches = 0;
    this._multiTouchHandled = false;
  }

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