<template>
  <div class="slider-wrapper" :style="wrapperStyle">
    
    <div class="slider-inner" ref="containerRef" :style="innerStyle">
      
      <div class="track-slot"></div>

      <div
        class="knob"
        :style="knobStyle"
        @mousedown="startDrag"
        @touchstart.prevent="startDrag"
      >
        <div class="knob-face"></div>
      </div>
      
    </div>
  </div>
</template>

<script setup>
import { ref, computed, watch } from 'vue';

const props = defineProps({
  modelValue: {
    type: Number,
    default: 0
  },
  // 新增 scale 属性，默认为 1 (原始大小)
  scale: {
    type: Number,
    default: 1.0
  }
});

const emit = defineEmits(['update:modelValue', 'change']);

// --- 内部常量定义 (基于原始设计尺寸) ---
const ORIGINAL_WIDTH = 40;  // 原始宽度 px
const ORIGINAL_HEIGHT = 150; // 原始高度 px
const STEPS = 4;
const STEP_DISTANCE = 40;
const KNOB_HEIGHT = 24;
const TRACK_PADDING_TOP = 2;

// --- 状态 ---
const currentIndex = ref(props.modelValue);

watch(() => props.modelValue, (newVal) => {
  currentIndex.value = newVal;
});

// --- 样式计算 ---

// 1. 外层容器样式：计算缩放后实际占用的宽高
const wrapperStyle = computed(() => ({
  width: `${ORIGINAL_WIDTH * props.scale}px`,
  height: `${ORIGINAL_HEIGHT * props.scale}px`,
}));

// 2. 内层容器样式：固定原始尺寸，使用 scale 缩放
const innerStyle = computed(() => ({
  width: `${ORIGINAL_WIDTH}px`,
  height: `${ORIGINAL_HEIGHT}px`,
  transform: `scale(${props.scale})`,
  transformOrigin: 'top left' // 关键：从左上角开始缩放，确保与外层容器对齐
}));

// 3. 旋钮位置样式
const knobStyle = computed(() => {
  const topOffset = TRACK_PADDING_TOP + (currentIndex.value * STEP_DISTANCE);
  return {
    transform: `translateY(${topOffset}px)`
  };
});

// --- 拖拽逻辑 (含缩放修正) ---
let isDragging = false;
let startMouseY = 0;
let startKnobTop = 0;

const startDrag = (e) => {
  isDragging = true;
  startMouseY = e.clientY || e.touches[0].clientY;
  startKnobTop = TRACK_PADDING_TOP + (currentIndex.value * STEP_DISTANCE);

  window.addEventListener('mousemove', onDrag);
  window.addEventListener('mouseup', stopDrag);
  window.addEventListener('touchmove', onDrag, { passive: false });
  window.addEventListener('touchend', stopDrag);
};

const onDrag = (e) => {
  if (!isDragging) return;
  if (e.cancelable) e.preventDefault();

  const currentMouseY = e.clientY || e.touches[0].clientY;
  
  // [关键修正]
  // 鼠标在屏幕上移动的距离 (screen delta)
  const screenDeltaY = currentMouseY - startMouseY;
  
  // 转换为组件内部的距离 (internal delta)
  // 比如：如果缩放是 0.5，屏幕移动 10px，相当于内部移动了 20px
  const internalDeltaY = screenDeltaY / props.scale;

  let newRawTop = startKnobTop + internalDeltaY;

  // 计算吸附
  let relativeTop = newRawTop - TRACK_PADDING_TOP;
  let newIndex = Math.round(relativeTop / STEP_DISTANCE);

  const maxIndex = STEPS - 1;
  if (newIndex < 0) newIndex = 0;
  if (newIndex > maxIndex) newIndex = maxIndex;

  if (newIndex !== currentIndex.value) {
    currentIndex.value = newIndex;
    emit('update:modelValue', newIndex);
    emit('change', newIndex);
  }
};

const stopDrag = () => {
  isDragging = false;
  window.removeEventListener('mousemove', onDrag);
  window.removeEventListener('mouseup', stopDrag);
  window.removeEventListener('touchmove', onDrag);
  window.removeEventListener('touchend', stopDrag);
};
</script>

<style scoped>
/* 样式部分主要针对 slider-inner 内部
  保持原本的尺寸定义即可，缩放由内联样式 style 处理 
*/

.slider-wrapper {
  /* 防止溢出裁剪阴影 */
  overflow: visible; 
  /* 禁止选中 */
  user-select: none;
  touch-action: none;
  /* 方便父级布局 */
  display: inline-block; 
  vertical-align: middle;
}

.slider-inner {
  position: relative;
  /* 这里的宽高现在由 innerStyle 动态控制，但写上默认值是个好习惯 */
  width: 40px; 
  height: 150px;
}

.track-slot {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 50%;
  transform: translateX(-50%);
  width: 8px;
  background-color: #1a1a1a;
  border-radius: 4px;
  box-shadow: 
    inset 1px 1px 3px rgba(0,0,0,0.7),
    inset -1px -1px 1px rgba(255,255,255,0.1);
}

.knob {
  position: absolute;
  top: 0;
  left: 50%;
  margin-left: -23px;
  width: 46px;
  height: 24px;
  z-index: 10;
  cursor: grab;
  transition: transform 0.2s cubic-bezier(0.25, 1, 0.5, 1);
  backface-visibility: hidden; /* 优化缩放后的渲染 */
}

.knob:active {
  cursor: grabbing;
}

.knob-face {
  width: 100%;
  height: 100%;
  background: linear-gradient(to bottom, #ffffff 0%, #e4e4e4 100%);
  border-radius: 4px;
  box-shadow: 
    inset 0 1px 0 rgba(255,255,255,1),
    inset 0 -1px 0 rgba(0,0,0,0.1),
    0 3px 6px rgba(0,0,0,0.35),
    0 0 0 1px rgba(0,0,0,0.08);
}
</style>