/**
 * 指标变化展示规则纯函数
 * 规则来源：design.md §8 变化颜色与箭头规则
 * 颜色映射：改善=绿 / 恶化=红 / 中性=灰
 */

/**
 * 由 good_direction × movement 推导展示样式
 * @param {string} goodDirection higher_is_better|lower_is_better|in_range_is_better|neutral
 * @param {string} movement up|down|flat
 * @returns {{trendLabel:string, cssClass:string, arrow:string}}
 */
export function resolveChangeStyle(goodDirection, movement) {
  var gd = goodDirection || 'neutral'
  var mv = movement || 'flat'
  if (mv === 'flat') {
    return { trendLabel: '中性', cssClass: 'flat', arrow: '→' }
  }
  // 是否"改善"：higher_is_better 升=改善；lower_is_better 降=改善；in_range 视区间判定（此处交给 withRange 变体）
  var isImprove = false
  if (gd === 'higher_is_better') {
    isImprove = mv === 'up'
  } else if (gd === 'lower_is_better') {
    isImprove = mv === 'down'
  } else {
    // neutral / in_range_is_better（一期 in_range 的管理端手配方向；区间内移动判定留二期，先按中性展示）
    return {
      trendLabel: '中性',
      cssClass: gd === 'in_range_is_better' ? 'neutral-up' : mv === 'up' ? 'neutral-up' : 'neutral-down',
      arrow: mv === 'up' ? '↑' : '↓'
    }
  }
  if (isImprove) {
    return { trendLabel: '改善', cssClass: gd === 'higher_is_better' ? 'impr-up' : 'impr-down', arrow: mv === 'up' ? '↑' : '↓' }
  }
  return { trendLabel: '恶化', cssClass: gd === 'higher_is_better' ? 'worst-down' : 'worst-up', arrow: mv === 'up' ? '↑' : '↓' }
}

/**
 * Δ 展示文本 "±x (±x%)"
 * @param {number|null} delta
 * @param {number|null} deltaPct
 * @returns {string}
 */
export function formatDelta(delta, deltaPct) {
  if (delta === null || delta === undefined || isNaN(delta)) return '--'
  var sign = delta > 0 ? '+' : ''
  if (deltaPct === null || deltaPct === undefined || isNaN(deltaPct)) {
    return sign + delta
  }
  var pctSign = deltaPct > 0 ? '+' : ''
  return sign + delta + ' (' + pctSign + deltaPct + '%)'
}

/**
 * CSS 颜色类：改善=green-text 恶化=red-text 中性=gray-text
 * @param {string} cssClass resolveChangeStyle 返回的类
 * @returns {string}
 */
export function colorClassFor(cssClass) {
  if (cssClass.indexOf('impr') === 0) return 'green-text'
  if (cssClass.indexOf('worst') === 0) return 'red-text'
  return 'gray-text'
}