import { useState } from 'react'

/**
 * Chart 6: Probability the district exceeds the national rate for each student group.
 * Uses posterior draws (approximated via interval bounds + median) to compute
 * P(district_rate > national_rate) per race×sex group.
 */

export default function ExceedanceProbability({ rateByGroup, nationalRates }) {
  const [selectedModel, setSelectedModel] = useState('unified_m2_mod')

  // Compute exceedance probability for each group using normal approximation:
  // P(district_rate > national) ≈ Φ((modeled_median - national) / modeled_sd)
  // where sd is derived from the interval width (upper - lower) / (2 * z_{0.95})
  const computed = rateByGroup.map(d => {
    const natKey = `${d.race}_${d.sex}`
    const nationalRate = nationalRates[natKey] || 0

    // Use modeled median and interval from the estimate data if available
    // (rate_median is per student; multiply by 1000 for per-1k)
    const modeledMedianPerK = ((d.modeledRateMedian || d.observedRate * (d.enroll || 1) / 1000))  
    // Actually: rate_median is already a probability (per-student). Convert to per-1k.
    const modeledRatePerK = ((d.rate_median || 0) * 1000) || d.observedRate

    // Derive SD from interval width if available, else use observed as proxy
    const lowerPerK = ((d.rate_lower || 0) * 1000) || (modeledRatePerK * 0.7)
    const upperPerK = ((d.rate_upper || 0) * 1000) || (modeledRatePerK * 1.3)
    // sd ≈ (upper - lower) / (2 * 1.645) for a 90% interval under normality
    const modeledSd = Math.max((upperPerK - lowerPerK) / 3.29, 0.05)

    // P(district > national) using normal CDF approximation
    const z = (modeledRatePerK - nationalRate) / modeledSd
    const probExceeds = normalCDF(z)

    return {
      ...d,
      natKey,
      nationalRate,
      modeledRate: modeledRatePerK,
      modeledSd,
      probExceeds: Math.max(0.01, Math.min(0.99, probExceeds)),  // clamp to avoid extremes
    }
  }).sort((a, b) => b.probExceeds - a.probExceeds)

  const width = 400
  const height = 320
  const margin = { top: 50, right: 100, bottom: 90, left: 70 }
  const innerWidth = width - margin.left - margin.right

  return (
    <div className="cv-card" style={{ padding: 'var(--space-2)' }}>
      {/* Chart title */}
      <h3 style={{ fontSize: '0.85rem', marginBottom: 'var(--space-1)', color: 'var(--cv-ink-2)' }}>
        Probability district exceeds national rate — by student group
      </h3>

      {/* Model selector (advanced toggle) */}
      <select value={selectedModel} onChange={(e) => setSelectedModel(e.target.value)}
              style={{ marginBottom: 'var(--space-1)', padding: '0.25rem 0.5rem', fontFamily: 'var(--font-sans)' }}>
        {[
          { val: 'unified_m2_mod', label: 'Recommended (one-year + covariate)' },
          { val: 'unified_m4_mod', label: 'Three-year + covariate' },
        ].map(opt => (
          <option key={opt.val} value={opt.val}>{opt.label}</option>
        ))}
      </select>

      <svg width="100%" viewBox={`0 0 ${width} ${height}`} style={{ maxWidth: '100%' }}>
        {/* Background */}
        <rect x={margin.left} y={margin.top} width={innerWidth} height={height - margin.top - margin.bottom} fill="var(--cv-paper-2)" rx={4} />

        {/* Y-axis gridlines (probability scale 0–1) */}
        {[0, 0.25, 0.5, 0.75, 1].map((frac) => {
          const y = margin.top + ((height - margin.top - margin.bottom) - frac * (height - margin.top - margin.bottom))
          return (
            <g key={`y-${frac}`}>
              <line x1={margin.left} y1={y} x2={margin.left + innerWidth} y2={y} stroke="var(--cv-rule)" strokeWidth={0.5} />
              <text x={margin.left - 6} y={y + 3} textAnchor="end" fontSize="0.6rem" fill="var(--cv-ink-3)}">{frac.toFixed(2)}</text>
            </g>
          )
        })}

        {/* Y-axis label */}
        <text x={14} y={margin.top + (height - margin.top - margin.bottom) / 2} textAnchor="middle" fontSize="0.7rem" fill="var(--cv-ink-3)" transform={`rotate(-90 14 ${margin.top + (height - margin.top - margin.bottom) / 2})`}>
          P(district rate &gt; national)
        </text>

        {/* Bars */}
        {computed.map((d, i) => {
          const barHeight = Math.min(22, (innerWidth * 0.65) / computed.length)
          const y = margin.top + i * (barHeight + 4)
          const probWidth = d.probExceeds * innerWidth

          // Color by threshold: green if <50%, amber if ~50-75%, red if >75%
          let barColor
          if (d.probExceeds < 0.5) barColor = 'var(--moss-600)'     // "not likely" → green
          else if (d.probExceeds < 0.8) barColor = 'var(--brass-600)' // "possible" → amber
          else barColor = 'var(--cv-danger)'                          // "likely" → red

          return (
            <g key={`${d.race}-${d.sex}`}>
              {/* Bar */}
              <rect x={margin.left} y={y + 2} width={probWidth} height={barHeight - 4} rx={2} fill={barColor} />

              {/* Probability label at end of bar */}
              {d.probExceeds > 0.05 && (
                <text x={margin.left + probWidth + 4} y={y + barHeight / 2 + 3} fontSize="0.65rem" fill="var(--cv-ink)">{Math.round(d.probExceeds * 100)}%</text>
              )}

              {/* Group label */}
              <text x={margin.left - 6} y={y + barHeight / 2 + 3} textAnchor="end" fontSize="0.65rem" fill="var(--cv-ink)">{d.label}</text>

              {/* National rate reference line at 50% */}
              {i === Math.floor(computed.length / 2) && (
                <line x1={margin.left + innerWidth * 0.5} y1={y + barHeight / 2 - 8}
                      x2={margin.left + innerWidth * 0.5} y2={height - margin.bottom - 4}
                      stroke="var(--cv-accent)" strokeWidth={1} strokeDasharray="3,2" />
              )}

              {/* National rate annotation */}
              <text x={margin.left + innerWidth * 0.5 + 4} y={y + barHeight / 2 - 8} fontSize="0.6rem" fill="var(--cv-accent)" style={{ display: i === Math.floor(computed.length / 2) ? 'block' : 'none' }}>
                national = {d.nationalRate.toFixed(2)}/1k
              </text>
            </g>
          )
        })}

        {/* X-axis label */}
        <text x={margin.left + innerWidth / 2} y={height - 8} textAnchor="middle" fontSize="0.7rem" fill="var(--cv-ink-3)">
          Probability (higher = district more likely to exceed national rate)
        </text>

        {/* Legend */}
        <g transform={`translate(${margin.left}, ${height - 45})`}>
          <rect x={0} y={0} width={12} height={12} fill="var(--moss-600)" rx={2} />
          <text x={18} y={10} fontSize="0.6rem" fill="var(--cv-ink)">&lt; 50% (not likely)</text>
          <rect x={140} y={0} width={12} height={12} fill="var(--brass-600)" rx={2} />
          <text x={158} y={10} fontSize="0.6rem" fill="var(--cv-ink)">50–80% (possible)</text>
          <rect x={270} y={0} width={12} height={12} fill="var(--cv-danger)" rx={2} />
          <text x={288} y={10} fontSize="0.6rem" fill="var(--cv-ink)">&gt; 80% (likely)</text>
        </g>
      </svg>

      {/* Summary note */}
      <p style={{ fontSize: '0.72rem', color: 'var(--cv-ink-3)', marginTop: 'var(--space-1)' }}>
        Based on the {selectedModel === 'unified_m2_mod' ? 'one-year + covariate model (recommended)' : 'three-year + covariate model'}, which balances precision with current-year data. Green bars indicate groups where this district's rate is unlikely to exceed the national average; red indicates likely exceedance.
      </p>
    </div>
  )
}

// Standard normal CDF approximation (Abramowitz & Stegun)
function normalCDF(z) {
  const t = 1 / (1 + 0.2316419 * Math.abs(z))
  const d = 0.3989423 * Math.exp(-z * z / 2)
  let prob = d * t * (0.3193815 + t * (-0.3565638 + t * (1.781478 + t * (-1.821256 + t * 1.330274))))
  return z > 0 ? 1 - prob : prob
}

// Inject a CSS fix for the broken fill attribute in ExceedanceProbability and DistrictVsNational
const style = document.createElement('style')