// 趋势徽标: 上升 / 下降 / 持平 / 震荡
// props:
//   trend: 'up' | 'down' | 'flat' | 'volatile'
//   showText: 是否显示文字 (默认 true)
const META = {
  up:       { icon: '\u2191', text: '上升' },
  down:     { icon: '\u2193', text: '下降' },
  flat:     { icon: '=',     text: '持平' },
  volatile: { icon: '\u223F', text: '震荡' },
}

// 根据最近 N 个数据点计算趋势:
//   - 数据不足 2 个 → flat
//   - 取最近 6 个点的变化, 整体涨幅 < 1% → flat
//   - 单调递增 → up, 单调递减 → down
//   - 其余 (有升有降) → volatile
// 返回: { trend, change }  (change 为百分比变化, 保留 1 位小数)
export function calcTrend(rows) {
  if (!rows || rows.length < 2) return { trend: 'flat', change: 0 }
  const N = Math.min(6, rows.length)
  const recent = rows.slice(-N).map((r) => r.value).filter((v) => typeof v === 'number')
  if (recent.length < 2) return { trend: 'flat', change: 0 }
  const first = recent[0]
  const last = recent[recent.length - 1]
  const change = first === 0 ? 0 : ((last - first) / Math.abs(first)) * 100
  if (Math.abs(change) < 1) return { trend: 'flat', change }
  let up = 0, down = 0
  for (let i = 1; i < recent.length; i++) {
    if (recent[i] > recent[i - 1]) up++
    else if (recent[i] < recent[i - 1]) down++
  }
  if (up === recent.length - 1) return { trend: 'up', change }
  if (down === recent.length - 1) return { trend: 'down', change }
  return { trend: 'volatile', change }
}

// 取数据序列最后一个有效点: { month, value } 或 null
export function lastPoint(data) {
  const rows = (data && data.rows) || []
  for (let i = rows.length - 1; i >= 0; i--) {
    if (rows[i] && typeof rows[i].value === 'number') return rows[i]
  }
  return null
}

export default function TrendBadge({ trend, showText = true }) {
  const m = META[trend] || META.flat
  return (
    <span className={'trend-badge trend-' + (trend || 'flat')}>
      <span className="trend-icon">{m.icon}</span>
      {showText && <span>{m.text}</span>}
    </span>
  )
}