// Estimated cost of the Climate Commitment Act to Washington on-road fuel users, 2023-2026 Q3.
// Two independent methods:
//   A. Allowance-cost method: quarterly auction settlement price x EPA CO2 per gallon x taxed gallons.
//   B. Measured-premium method (gasoline only): annual difference-in-differences effect x taxed gallons.
// Usage: node cost.js <did_results.json> <CPIAUCSL.csv> <out.json>
const fs = require('fs');
const [resFile, cpiFile, outFile] = process.argv.slice(2);
const res = JSON.parse(fs.readFileSync(resFile, 'utf8'));

// Ecology quarterly auction settlement prices, current vintage ($/allowance = $/t CO2e)
const AUCTIONS = {
  '2023Q1': 48.50, '2023Q2': 56.01, '2023Q3': 63.03, '2023Q4': 51.89,
  '2024Q1': 25.76, '2024Q2': 29.92, '2024Q3': 29.88, '2024Q4': 40.26,
  '2025Q1': 50.00, '2025Q2': 58.51, '2025Q3': 64.30, '2025Q4': 70.86,
  '2026Q1': 65.26, '2026Q2': 64.56, '2026Q3': 39.50,
};
// EPA 40 CFR Part 98 Subpart MM, Table MM-1 (kg CO2 per gallon)
const KG_GASOLINE = 8.78, KG_DIESEL = 10.21;
const ETHANOL_SHARE = 0.10; // E10; biogenic CO2 from ethanol is not a CCA compliance obligation
const kgGas = KG_GASOLINE * (1 - ETHANOL_SHARE);

// Washington taxed motor fuel, million gallons, by state fiscal year (July-June).
// Source: Transportation Revenue Forecast Council, February 2026 forecast, Vol. II, Table A.1.
// FY2018-FY2025 are actuals; FY2026-FY2027 are forecasts.
const FY = {
  gasoline: { 2023: 2621, 2024: 2612, 2025: 2578, 2026: 2461, 2027: 2420 },
  diesel: { 2023: 757, 2024: 691, 2025: 694, 2026: 673, 2027: 661 },
};
// Quarter q of calendar year y falls in FY y (Q1, Q2) or FY y+1 (Q3, Q4); quarterly gallons = FY/4.
const fyOf = (q) => (+q[5] <= 2 ? +q.slice(0, 4) : +q.slice(0, 4) + 1);
const quarterGallons = (fuel, q) => (FY[fuel][fyOf(q)] * 1e6) / 4;
const isForecastFy = (q) => fyOf(q) >= 2026;

// CPI for converting the real (Jan-2024 $) measured effect back to nominal dollars
const cpi = new Map();
for (const l of fs.readFileSync(cpiFile, 'utf8').trim().split(/\r?\n/).slice(1)) { const [d, v] = l.split(','); if (v) cpi.set(d.slice(0, 7), +v); }
cpi.set('2025-10', (cpi.get('2025-09') + cpi.get('2025-11')) / 2);
const base = cpi.get('2024-01');
const lastCpi = [...cpi.values()].pop();
const cpiQ = (q) => { const y = q.slice(0, 4), m0 = (+q[5] - 1) * 3; const v = [1, 2, 3].map((i) => cpi.get(`${y}-${String(m0 + i).padStart(2, '0')}`) ?? lastCpi); return v.reduce((a, b) => a + b) / 3; };

const CONTROL = '7 EIA states w/o fuel carbon pricing';
const quarters = Object.keys(AUCTIONS);
const rows = quarters.map((q) => {
  const p = AUCTIONS[q];
  const gasCents = (p * kgGas) / 10; // $/t * kg/gal / 1000 * 100
  const dieselCents = (p * KG_DIESEL) / 10;
  const gGal = quarterGallons('gasoline', q), dGal = quarterGallons('diesel', q);
  const measuredReal = res.quarterly[CONTROL].effects.find((e) => e.period === q).effect; // $/gal, Jan-2024 $
  const measuredNominal = (measuredReal * cpiQ(q)) / base;
  return {
    quarter: q, allowancePrice: p,
    gasolineCarbonCostCentsPerGal: +gasCents.toFixed(1), dieselCarbonCostCentsPerGal: +dieselCents.toFixed(1),
    gasolineGallonsMillions: gGal / 1e6, dieselGallonsMillions: dGal / 1e6, gallonsAreForecast: isForecastFy(q),
    allowanceMethodGasolineUsdMillions: +((gasCents / 100) * gGal / 1e6).toFixed(1),
    allowanceMethodDieselUsdMillions: +((dieselCents / 100) * dGal / 1e6).toFixed(1),
    measuredGasolinePremiumCentsNominal: +(measuredNominal * 100).toFixed(1),
    measuredMethodGasolineUsdMillions: +(measuredNominal * gGal / 1e6).toFixed(1),
  };
});

const byYear = {};
for (const r of rows) {
  const y = r.quarter.slice(0, 4);
  const t = (byYear[y] ??= { year: y, quarters: 0, allowanceGasoline: 0, allowanceDiesel: 0, measuredGasoline: 0 });
  t.quarters++; t.allowanceGasoline += r.allowanceMethodGasolineUsdMillions; t.allowanceDiesel += r.allowanceMethodDieselUsdMillions; t.measuredGasoline += r.measuredMethodGasolineUsdMillions;
}
const totals = { allowanceGasoline: 0, allowanceDiesel: 0, measuredGasoline: 0 };
console.log('Year  Qtrs  Allowance-method gas $M  diesel $M  total $M   Measured-premium gas $M');
for (const t of Object.values(byYear)) {
  for (const k of Object.keys(totals)) totals[k] += t[k];
  console.log(`${t.year}  ${t.quarters}     ${t.allowanceGasoline.toFixed(0).padStart(8)}             ${t.allowanceDiesel.toFixed(0).padStart(6)}   ${(t.allowanceGasoline + t.allowanceDiesel).toFixed(0).padStart(7)}   ${t.measuredGasoline.toFixed(0).padStart(10)}`);
}
console.log(`Total ${quarters.length}q   ${totals.allowanceGasoline.toFixed(0).padStart(8)}             ${totals.allowanceDiesel.toFixed(0).padStart(6)}   ${(totals.allowanceGasoline + totals.allowanceDiesel).toFixed(0).padStart(7)}   ${totals.measuredGasoline.toFixed(0).padStart(10)}`);
console.log('\nPer-gallon carbon cost (cents): ' + rows.map((r) => `${r.quarter} gas ${r.gasolineCarbonCostCentsPerGal} / diesel ${r.dieselCarbonCostCentsPerGal}`).join('; '));
fs.writeFileSync(outFile, JSON.stringify({ assumptions: { kgGas, KG_DIESEL, ETHANOL_SHARE, control: CONTROL, gallonsSource: 'TRFC Feb 2026 Vol II Table A.1' }, quarterly: rows, annual: Object.values(byYear), totals }, null, 2));