// ============================================================
// FENTON 2013 — preterm growth LMS for weight-for-GA. Table
// ported VERBATIM from public/js/calculators.js:1168-1183
// (15 GA weeks × 2 sexes × {L,M,S}). Parity against the vanilla
// implementation pinned by e2e/fixtures/calc-vectors.json +
// fenton.test.ts.
//
// Reference:
//   Fenton TR, Kim JH. A systematic review and meta-analysis
//   to revise the Fenton growth chart for preterm infants.
//   BMC Pediatr 2013;13:59.
// ============================================================

export type Sex = 'male' | 'female';
export interface Lms { L: number; M: number; S: number }

export interface FentonResult {
  L: number;
  M: number;
  S: number;
  z: number;
  percentile: number;
}

// Verbatim from calculators.js:1168-1183.
export const fentonLMS: Record<Sex, Record<number, Lms>> = {
  male: {
    22: { L: 0.21,  M: 496,  S: 0.17 }, 24: { L: 0.21,  M: 660,  S: 0.17 }, 26: { L: 0.21,  M: 870,  S: 0.16 },
    28: { L: 0.20,  M: 1124, S: 0.15 }, 30: { L: 0.18,  M: 1430, S: 0.14 }, 32: { L: 0.15,  M: 1795, S: 0.14 },
    34: { L: 0.12,  M: 2230, S: 0.13 }, 36: { L: 0.08,  M: 2710, S: 0.13 }, 38: { L: 0.04,  M: 3195, S: 0.12 },
    40: { L: 0.01,  M: 3530, S: 0.12 }, 42: { L: -0.02, M: 3820, S: 0.12 }, 44: { L: -0.04, M: 4200, S: 0.12 },
    46: { L: -0.06, M: 4680, S: 0.12 }, 48: { L: -0.07, M: 5200, S: 0.12 }, 50: { L: -0.08, M: 5760, S: 0.12 },
  },
  female: {
    22: { L: 0.23,  M: 474,  S: 0.17 }, 24: { L: 0.22,  M: 610,  S: 0.17 }, 26: { L: 0.22,  M: 810,  S: 0.16 },
    28: { L: 0.21,  M: 1040, S: 0.15 }, 30: { L: 0.19,  M: 1330, S: 0.14 }, 32: { L: 0.16,  M: 1680, S: 0.14 },
    34: { L: 0.12,  M: 2090, S: 0.13 }, 36: { L: 0.08,  M: 2540, S: 0.13 }, 38: { L: 0.04,  M: 3000, S: 0.12 },
    40: { L: 0.01,  M: 3340, S: 0.12 }, 42: { L: -0.02, M: 3630, S: 0.12 }, 44: { L: -0.04, M: 4010, S: 0.12 },
    46: { L: -0.06, M: 4470, S: 0.12 }, 48: { L: -0.07, M: 4970, S: 0.12 }, 50: { L: -0.08, M: 5510, S: 0.12 },
  },
};

// Verbatim from calculators.js:2299-2311.
export function interpolateLMS(table: Record<number, Lms>, val: number): Lms {
  const keys = Object.keys(table).map(Number).sort((a, b) => a - b);
  if (val <= keys[0]) return table[keys[0]];
  if (val >= keys[keys.length - 1]) return table[keys[keys.length - 1]];
  for (let i = 0; i < keys.length - 1; i++) {
    if (val >= keys[i] && val <= keys[i + 1]) {
      const t = (val - keys[i]) / (keys[i + 1] - keys[i]);
      const lms1 = table[keys[i]];
      const lms2 = table[keys[i + 1]];
      return {
        L: lms1.L + t * (lms2.L - lms1.L),
        M: lms1.M + t * (lms2.M - lms1.M),
        S: lms1.S + t * (lms2.S - lms1.S),
      };
    }
  }
  return table[keys[0]];
}

// Verbatim from calculators.js:2313-2316.
export function calcZ(value: number, L: number, M: number, S: number): number {
  if (L === 0) return Math.log(value / M) / S;
  return (Math.pow(value / M, L) - 1) / (L * S);
}

// Abramowitz & Stegun normal CDF approximation, verbatim from
// calculators.js:2318-2326.
export function zToPercentile(z: number): number {
  const t = 1 / (1 + 0.2316419 * Math.abs(z));
  const d = 0.3989423 * Math.exp(-z * z / 2);
  let p = d * t * (0.3193815 + t * (-0.3565638 + t * (1.781478 + t * (-1.821256 + t * 1.330274))));
  if (z > 0) p = 1 - p;
  return p * 100;
}

export function fentonWeightForAge(gaWeeks: number, weightGrams: number, sex: Sex): FentonResult {
  const lms = interpolateLMS(fentonLMS[sex], gaWeeks);
  const z = calcZ(weightGrams, lms.L, lms.M, lms.S);
  const percentile = zToPercentile(z);
  return { L: lms.L, M: lms.M, S: lms.S, z, percentile };
}

// Clinical classification — per AAP 2017 / Fenton 2013:
//   SGA: <10th percentile, LGA: >90th, AGA: between.
export type SizeForAge = 'SGA' | 'AGA' | 'LGA';
export function classifySizeForAge(percentile: number): SizeForAge {
  if (percentile < 10) return 'SGA';
  if (percentile > 90) return 'LGA';
  return 'AGA';
}