<template>
  <div class="kole-calendar">
    <div class="kole-calendar-head">
      <button class="kole-calendar-nav" @click="prev">‹</button>
      <span class="kole-calendar-title">{{ viewY }} 年 {{ viewM + 1 }} 月</span>
      <button class="kole-calendar-nav" @click="next">›</button>
    </div>
    <div class="kole-calendar-week">
      <span class="kole-calendar-weekday" v-for="w in weeks" :key="w">{{ w }}</span>
    </div>
    <div class="kole-calendar-grid">
      <div v-for="(c, i) in cells" :key="i" class="kole-calendar-cell"
           :class="{ 'is-out': c.out, 'is-today': c.today, 'is-selected': c.key === selected }"
           @click="pick(c)">{{ c.day }}</div>
    </div>
  </div>
</template>

<script>
export default {
  name: 'KoleCalendar',
  props: { value: { type: String, default: '' } },
  data: function () {
    var n = new Date();
    return {
      weeks: ['日', '一', '二', '三', '四', '五', '六'],
      viewY: n.getFullYear(), viewM: n.getMonth(),
      selected: this.value, today: this.fmt(n)
    };
  },
  computed: {
    cells: function () {
      var first = new Date(this.viewY, this.viewM, 1).getDay();
      var days = new Date(this.viewY, this.viewM + 1, 0).getDate();
      var prevDays = new Date(this.viewY, this.viewM, 0).getDate();
      var arr = [];
      var self = this;
      for (var i = 0; i < first; i++) {
        var pd = prevDays - first + 1 + i;
        var pm = this.viewM - 1, py = this.viewY; if (pm < 0) { pm = 11; py--; }
        arr.push({ day: pd, out: true, key: self.fmt(new Date(py, pm, pd)) });
      }
      for (var d = 1; d <= days; d++) {
        var k = self.fmt(new Date(this.viewY, this.viewM, d));
        arr.push({ day: d, out: false, today: k === this.today, key: k });
      }
      var tail = (7 - (arr.length % 7)) % 7;
      for (var t = 1; t <= tail; t++) {
        var nm = this.viewM + 1, ny = this.viewY; if (nm > 11) { nm = 0; ny++; }
        arr.push({ day: t, out: true, key: self.fmt(new Date(ny, nm, t)) });
      }
      return arr;
    }
  },
  methods: {
    fmt: function (dt) {
      var p = function (n) { return n < 10 ? '0' + n : '' + n; };
      return dt.getFullYear() + '-' + p(dt.getMonth() + 1) + '-' + p(dt.getDate());
    },
    prev: function () { this.viewM--; if (this.viewM < 0) { this.viewM = 11; this.viewY--; } },
    next: function () { this.viewM++; if (this.viewM > 11) { this.viewM = 0; this.viewY++; } },
    pick: function (c) {
      this.selected = c.key;
      this.viewY = parseInt(c.key.slice(0, 4), 10);
      this.viewM = parseInt(c.key.slice(5, 7), 10) - 1;
      this.$emit('input', c.key);
      this.$emit('change', c.key);
    }
  }
};
</script>

<style src="./Calendar.css"></style>
