import type { ResearchCompany, ResearchObservation, ResearchSnapshot } from "./ai-research";

export type IncomePoint = { company: ResearchCompany; observation: ResearchObservation; value: number };
export type IncomeStats = {
  n: number; mean: number; median: number; min: number; max: number;
  sampleDeviation: number | null; cv: number | null; meanMedianRatio: number | null;
  largestShare: number | null; meanWithoutLargest: number | null; largestRemovalDrop: number | null;
};

/** Describes the supplied sample only; missing values never become zero. */
export function describeIncome(values: number[]): IncomeStats | null {
  if (!values.length || values.some((value) => !Number.isFinite(value) || value < 0)) return null;
  const ordered = [...values].sort((a, b) => a - b);
  const n = ordered.length;
  const total = ordered.reduce((sum, value) => sum + value, 0);
  const mean = total / n;
  const median = n % 2 ? ordered[(n - 1) / 2] : (ordered[n / 2 - 1] + ordered[n / 2]) / 2;
  const sampleDeviation = n > 1 ? Math.sqrt(ordered.reduce((sum, value) => sum + (value - mean) ** 2, 0) / (n - 1)) : null;
  const max = ordered[n - 1];
  const meanWithoutLargest = n > 1 ? (total - max) / (n - 1) : null;
  return { n, mean, median, min: ordered[0], max, sampleDeviation,
    cv: sampleDeviation !== null && mean > 0 ? sampleDeviation / mean : null,
    meanMedianRatio: median > 0 ? mean / median : null,
    largestShare: total > 0 ? max / total : null, meanWithoutLargest,
    largestRemovalDrop: meanWithoutLargest !== null && mean > 0 ? (mean - meanWithoutLargest) / mean : null };
}

function calendarDay(value: string | undefined): number | null {
  if (!value || !/^\d{4}-\d{2}-\d{2}$/.test(value)) return null;
  const time = Date.parse(`${value}T00:00:00Z`);
  return Number.isFinite(time) && new Date(time).toISOString().slice(0, 10) === value ? time / 86400000 : null;
}

/** Latest dated platform MRR per product, never ARR, cash collections or estimates. */
export function platformIncomeSample(snapshot: ResearchSnapshot, options: {
  windowDays: number | null; foundedYear?: number; annualize?: boolean;
}) {
  const end = calendarDay(snapshot.asOf);
  if (end === null || (options.windowDays !== null && (!Number.isInteger(options.windowDays) || options.windowDays < 0)))
    throw new Error("Invalid income sample window");
  const companies = new Map(snapshot.companies.map((company) => [company.id, company]));
  const latest = new Map<string, ResearchObservation>();
  const excluded: { observation: ResearchObservation; reason: string }[] = [];
  const candidates = snapshot.observations.filter((o) => o.selection === "platform" && o.metric === "mrr");
  for (const observation of candidates) {
    const company = companies.get(observation.company);
    const day = calendarDay(observation.observedAt);
    let reason = "";
    if (!company || ![2025, 2026].includes(company.year ?? 0)) reason = "创立年份未纳入2025—2026组";
    else if (options.foundedYear && company.year !== options.foundedYear) reason = "不属于所选创立年份";
    else if (observation.origin !== "payment-platform" || observation.unit !== "USD" || observation.bound !== "=" ||
        observation.comparisonGroup !== "trustmrr-usd-mrr" || !observation.provider || !Number.isFinite(observation.value) || observation.value < 0)
      reason = "来源、币种、指标或数值口径不满足条件";
    else if (day === null) reason = "缺少有效数据日期";
    else if (day > end) reason = "数据日期晚于研究截止日";
    else if (options.windowDays !== null && end - day > options.windowDays) reason = "最后同步日期超出所选窗口";
    if (reason) { excluded.push({ observation, reason }); continue; }
    const previous = latest.get(observation.company);
    if (!previous || observation.observedAt! > previous.observedAt!) {
      if (previous) excluded.push({ observation: previous, reason: "同一产品的较早观测" });
      latest.set(observation.company, observation);
    } else excluded.push({ observation, reason: "同一产品已选较新或同日观测" });
  }
  const points: IncomePoint[] = [...latest.values()].map((observation) => ({
    company: companies.get(observation.company)!, observation,
    value: observation.value * (options.annualize ? 12 : 1),
  }));
  return { points, excluded };
}

export function groupIncome(points: IncomePoint[], splitModels = true) {
  const groups = new Map<string, { category: string; provider: string; model: string; points: IncomePoint[] }>();
  for (const point of points) {
    const category = point.company.cat;
    const provider = point.observation.provider!;
    const model = splitModels ? point.company.businessModel ?? "收费模式未核验" : "全部收费模式";
    const key = JSON.stringify([category, provider, model]);
    if (!groups.has(key)) groups.set(key, { category, provider, model, points: [] });
    groups.get(key)!.points.push(point);
  }
  return [...groups.entries()].map(([key, group]) => ({ key, ...group, stats: describeIncome(group.points.map((point) => point.value))! }));
}