/**
 * Returns Top source % and HHI-based traffic light (HHI hidden from UI)
 * Uses Herfindahl-Hirschman Index internally but only exposes traffic light color
 */
export const useConcentration = () => {
  const calculateTopSourcePct = (revenueShares: number[]): number => {
    if (revenueShares.length === 0) return 0
    return Math.max(...revenueShares)
  }
  
  const calculateHHI = (revenueShares: number[]): number => {
    // HHI = sum of squared market shares (as percentages)
    return revenueShares.reduce((sum, share) => sum + (share * share), 0)
  }
  
  const getConcentrationStatus = (topSourcePct: number, hhi: number): 'green' | 'yellow' | 'red' => {
    // Primary threshold based on top source %
    if (topSourcePct > 50) return 'red'
    if (topSourcePct > 35) return 'yellow'
    
    // Secondary check using HHI for more nuanced analysis
    if (hhi > 2500) return 'red'  // Highly concentrated
    if (hhi > 1500) return 'yellow'  // Moderately concentrated
    
    return 'green'
  }
  
  const getConcentrationMessage = (status: 'green' | 'yellow' | 'red'): string => {
    switch (status) {
      case 'red':
        return 'Most of your money comes from one place. Add another stream to reduce risk.'
      case 'yellow':
        return 'Revenue somewhat concentrated. Consider diversifying further.'
      case 'green':
        return 'Good revenue diversification.'
    }
  }
  
  const analyzeConcentration = (revenueStreams: Array<{ targetPct: number }>) => {
    const shares = revenueStreams.map(stream => stream.targetPct || 0)
    const topSourcePct = calculateTopSourcePct(shares)
    const hhi = calculateHHI(shares)
    const status = getConcentrationStatus(topSourcePct, hhi)
    
    return {
      topSourcePct,
      status,
      message: getConcentrationMessage(status)
      // Note: HHI is deliberately not exposed in return
    }
  }
  
  return {
    calculateTopSourcePct,
    getConcentrationStatus,
    getConcentrationMessage,
    analyzeConcentration
  }
}