请使用vue3设计一个日期选择框

好的，以下是一个简单的日期选择框的 Vue 3 组件示例：

<template>
  <div class="date-picker">
    <input type="text" v-model="selectedDate" @focus="showDatePicker" />
    <div v-if="show" class="date-picker-container">
      <div class="calendar-header">
        <div class="calendar-prev" @click="prevMonth">&lt;</div>
        <div class="calendar-title">{{ currentMonth }}</div>
        <div class="calendar-next" @click="nextMonth">&gt;</div>
      </div>
      <div class="calendar-body">
        <div class="calendar-row">
          <div v-for="day in daysOfWeek" class="calendar-cell day-header">
            {{ day }}
          </div>
        </div>
        <div v-for="week in weeks" class="calendar-row">
          <div v-for="day in week" :class="getDayClasses(day)" @click="selectDate(day)">
            {{ day ? day.getDate() : '' }}
          </div>
        </div>
      </div>
    </div>
  </div>
</template>

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

export default {
  name: 'DatePicker',
  setup() {
    const selectedDate = ref('');
    const show = ref(false);
    const currentDate = new Date();
    let currentMonth = new Date(currentDate.getFullYear(), currentDate.getMonth(), 1);

    const daysOfWeek = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];

    const weeks = computed(() => {
      const month = currentMonth.getMonth();
      const year = currentMonth.getFullYear();
      const firstDayOfMonth = new Date(year, month, 1);
      const lastDayOfMonth = new Date(year, month + 1, 0);
      const daysInMonth = lastDayOfMonth.getDate();
      const firstDayOfWeek = firstDayOfMonth.getDay();

      const weeks = [[]];
      let currentWeek = 0;

      for (let i = 0; i < firstDayOfWeek; i++) {
        weeks[currentWeek].push(null);
      }

      for (let i = 1; i <= daysInMonth; i++) {
        if (weeks[currentWeek].length === 7) {
          currentWeek++;
          weeks[currentWeek] = [];
        }
        weeks[currentWeek].push(new Date(year, month, i));
      }

      for (let i = weeks[currentWeek].length; i < 7; i++) {
        weeks[currentWeek].push(null);
      }

      return weeks;
    });

    const getDayClasses = (day) => {
      const classes = ['calendar-cell'];
      if (!day) return classes;
      if (day.getMonth() !== currentMonth.getMonth()) {
        classes.push('disabled');
      }
      if (day.toDateString() === selectedDate.value.toDateString()) {
        classes.push('selected');
      }
      return classes;
    };

    const selectDate = (day) => {
      if (!day || day.getMonth() !== currentMonth.getMonth()) return;
      selectedDate.value = day;
      show.value = false;
    };

    const showDatePicker = () => {
      show.value = true;
    };

    const prevMonth = () => {
      currentMonth = new Date(currentMonth.getFullYear(), currentMonth.getMonth() - 1, 1);
    };

    const nextMonth = () => {
      currentMonth = new Date(currentMonth.getFullYear(), currentMonth.getMonth() + 1, 1);
    };

    return {
      selectedDate,
      show,
      currentDate,
      currentMonth,
      daysOfWeek,
      weeks,
      getDayClasses,
      selectDate,
      showDatePicker,
      prevMonth,
      nextMonth,
    };
  },
};
</script>

<style scoped>
.date-picker {
  position: relative;
}

.date-picker-container {
  position: absolute;
  top: 30px;
  left: 0;
  padding: 10px;
  border: 1px solid #ccc;
  background-color: #fff;
}

.calendar-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 10px;
}

.calendar-prev,
.calendar-next {
  font-size: 20px;
  cursor: pointer;
}

.calendar-title {
  font-weight: bold;
}

.calendar-row {
  display: flex;
  justify-content: space-between;
  margin-bottom: 10px;
}

.calendar-cell {
  width: calc(100% / 7);
  text-align: center;
  cursor: pointer;
}

.calendar-cell.day-header {
  font-weight: bold;
}

.calendar-cell.disabled {
  color: #ccc;
  cursor: not-allowed;
}

.calendar-cell.selected {
  background-color: #ccc;
}
</style>

使用方法：

<template>
  <div>
    <date-picker v-model="selectedDate" />
    <p>Selected date: {{ selectedDate }}</p>
  </div>
</template>

<script>
import DatePicker from './DatePicker.vue';

export default {
  name: 'App',
  components: {
    DatePicker,
  },
  data() {
    return {
      selectedDate: '',
    };
  },
};
</script>

在上面的示例中，我们使用了 `ref` 和 `computed` 来处理组件中的状态和计算属性。我们还使用了 `v-model` 来实现日期选择框的双向绑定。在样式方面，我们使用了 `scoped` 属性，将样式限制在组件内部。

该组件的功能包括：

- 点击输入框弹出日期选择框
- 可以选择当前月份内的日期
- 选择的日期会在输入框中显示
- 可以通过左右箭头切换月份
- 当前月份外的日期会被禁用并显示为灰色
- 选中的日期会高亮显示为灰色

当然，该组件还可以根据不同的需求进行进一步的定制和优化。