import { median } from '@rareindex/shared';

export interface GradedSale {
  assetId: string;
  grader: string | null;
  grade: string | null;
  priceUsd: number;
}

export interface GradePremium {
  grader: string;
  grade: string;
  marketMultiplier: number;
  sampleSize: number;
}

/**
 * Empirical grade premiums (§118): for each (grader, grade), the median ratio of a graded sale to
 * the median raw/ungraded (or reference-grade) price of the SAME asset. Computed per category from
 * paired evidence only — never assumed across graders.
 */
export function computeGradePremiums(sales: GradedSale[], opts: { referenceKey?: string; minPairs?: number } = {}): GradePremium[] {
  const minPairs = opts.minPairs ?? 8;
  const byAsset = new Map<string, GradedSale[]>();
  for (const s of sales) if (s.priceUsd > 0) byAsset.set(s.assetId, [...(byAsset.get(s.assetId) ?? []), s]);
  const ratios = new Map<string, number[]>();
  for (const list of byAsset.values()) {
    const key = (s: GradedSale) => (s.grader && s.grade ? `${s.grader}|${s.grade}` : 'raw');
    const groups = new Map<string, number[]>();
    for (const s of list) groups.set(key(s), [...(groups.get(key(s)) ?? []), s.priceUsd]);
    const refKey = opts.referenceKey ?? 'raw';
    let ref = median(groups.get(refKey) ?? []);
    if (ref === null) {
      // fall back to the most common graded key for this asset as reference
      const best = [...groups.entries()].filter(([k]) => k !== refKey).sort((a, b) => b[1].length - a[1].length)[0];
      if (!best || best[1].length < 2) continue;
      ref = median(best[1]);
      // express others relative to that grade, then to raw is impossible → skip unless raw exists
      continue;
    }
    for (const [k, prices] of groups) {
      if (k === refKey) continue;
      const m = median(prices)!;
      ratios.set(k, [...(ratios.get(k) ?? []), m / ref]);
    }
  }
  const out: GradePremium[] = [];
  for (const [k, rs] of ratios) {
    if (rs.length < minPairs) continue;
    const [grader, grade] = k.split('|') as [string, string];
    out.push({ grader, grade, marketMultiplier: Math.round(median(rs)! * 1000) / 1000, sampleSize: rs.length });
  }
  return out.sort((a, b) => a.grader.localeCompare(b.grader) || Number(a.grade) - Number(b.grade));
}

/** Adjustment factor target/source from premium tables (both relative to raw). null when either is unknown. */
export function adjustmentFactor(premiums: GradePremium[], source: { grader: string | null; grade: string | null }, target: { grader: string | null; grade: string | null }): number | null {
  const mult = (g: { grader: string | null; grade: string | null }): number | null => {
    if (!g.grader || !g.grade) return 1; // raw
    const p = premiums.find((x) => x.grader === g.grader && x.grade === g.grade);
    return p ? p.marketMultiplier : null;
  };
  const s = mult(source);
  const t = mult(target);
  if (s === null || t === null || s <= 0) return null;
  return t / s;
}