import type { Candle, Pair } from '../types';
import { runBacktest, type BacktestConfig } from './runner';
import { computeMetrics, type Metrics, type EquityPoint } from './metrics';
import type { StrategyParams } from '../strategy/donchian-trend';
import type { ClosedTrade } from '../engine/portfolio';

const DAY = 24 * 60 * 60 * 1000;

export interface Window {
  trainFrom: number;
  trainTo: number;
  testFrom: number;
  testTo: number;
}

/**
 * Rollierende Train/Test-Fenster. Hinweis: Im ersten Fenster sind die ersten
 * ~EMA200-Perioden (≈33 Tage auf 4h) Indikator-Cold-Start — effektive
 * Train-Länge von Fenster 0 ist entsprechend kürzer als bei späteren Fenstern.
 */
export function buildWindows(dataFrom: number, dataTo: number, trainDays = 120, testDays = 30, stepDays = 30): Window[] {
  const out: Window[] = [];
  for (let start = dataFrom; start + (trainDays + testDays) * DAY <= dataTo; start += stepDays * DAY) {
    const trainTo = start + trainDays * DAY;
    out.push({ trainFrom: start, trainTo, testFrom: trainTo, testTo: trainTo + testDays * DAY });
  }
  return out;
}

export const PARAM_GRID: StrategyParams[] = [20, 40, 55].flatMap((donchianPeriod) =>
  [2, 3, 4].flatMap((atrMultiplier) =>
    [100, 200].map((trendEmaPeriod) => ({ donchianPeriod, atrPeriod: 14, atrMultiplier, trendEmaPeriod })),
  ),
);

export interface WindowResult {
  window: Window;
  bestParams: StrategyParams;
  trainMetrics: Metrics;
  testMetrics: Metrics;
  testTrades: ClosedTrade[];
  testEquityCurve: EquityPoint[];
}

export interface GateInput {
  oosProfitFactor: number;
  oosTrades: number;
  oosMaxDrawdownPct: number;
  worstWindow: { profitFactor: number; trades: number };
  avgTrainPf: number;
}

export interface GateCheck {
  name: string;
  pass: boolean;
  value: number;
  threshold: number;
}

export interface GateResult {
  pass: boolean;
  checks: GateCheck[];
}

/** Schlechtestes Test-Fenster UNTER den für Check 4 relevanten (>= 5 Trades). */
export function pickWorstEligibleWindow(metricsList: { profitFactor: number; trades: number }[]): { profitFactor: number; trades: number } {
  return metricsList
    .filter((m) => m.trades >= 5)
    .reduce(
      (acc, m) => (m.profitFactor < acc.profitFactor ? { profitFactor: m.profitFactor, trades: m.trades } : acc),
      { profitFactor: Infinity, trades: 0 },
    );
}

export function evaluateGate(g: GateInput): GateResult {
  const overfitRatio = g.oosProfitFactor > 0 ? g.avgTrainPf / g.oosProfitFactor : Infinity;
  const windowFail = g.worstWindow.trades >= 5 && g.worstWindow.profitFactor < 0.5;
  const checks: GateCheck[] = [
    { name: 'OOS-ProfitFactor >= 1.2', pass: g.oosProfitFactor >= 1.2, value: g.oosProfitFactor, threshold: 1.2 },
    { name: 'OOS-Trades >= 25', pass: g.oosTrades >= 25, value: g.oosTrades, threshold: 25 },
    { name: 'OOS-MaxDrawdown <= 25%', pass: g.oosMaxDrawdownPct <= 0.25, value: g.oosMaxDrawdownPct, threshold: 0.25 },
    { name: 'kein Fenster PF < 0.5 (bei >= 5 Trades)', pass: !windowFail, value: g.worstWindow.profitFactor, threshold: 0.5 },
    { name: 'Train-PF / OOS-PF < 2 (Overfitting)', pass: overfitRatio < 2, value: overfitRatio, threshold: 2 },
  ];
  return { pass: checks.every((c) => c.pass), checks };
}

export interface WalkForwardResult {
  windows: WindowResult[];
  oosMetrics: Metrics;
  oosEquityCurve: EquityPoint[];
  gate: GateResult;
}

type BaseConfig = Omit<BacktestConfig, 'params' | 'tradeFrom' | 'tradeTo'>;

/** PF-Vergleich mit Infinity-Handling: Infinity schlägt alles, Tie-Break TotalPnl. */
function better(a: Metrics, b: Metrics): boolean {
  if (a.profitFactor !== b.profitFactor) return a.profitFactor > b.profitFactor;
  return a.totalPnl > b.totalPnl;
}

export function runWalkForward(
  candles15ByPair: Map<Pair, Candle[]>,
  baseCfg: BaseConfig,
  dataFrom: number,
  dataTo: number,
  onProgress?: (msg: string) => void,
): WalkForwardResult {
  const windows = buildWindows(dataFrom, dataTo);
  const results: WindowResult[] = [];

  for (const [wi, w] of windows.entries()) {
    let bestParams = PARAM_GRID[0];
    let bestMetrics: Metrics | null = null;
    let bestEligible = false;

    for (const params of PARAM_GRID) {
      const r = runBacktest(candles15ByPair, { ...baseCfg, params, tradeFrom: w.trainFrom, tradeTo: w.trainTo });
      const m = computeMetrics(r.trades, r.equityCurve, baseCfg.startCapital);
      const eligible = m.trades >= 5;
      const wins =
        bestMetrics === null ||
        (eligible && !bestEligible) ||
        (eligible === bestEligible && (eligible ? better(m, bestMetrics) : m.trades > bestMetrics.trades));
      if (wins) {
        bestParams = params;
        bestMetrics = m;
        bestEligible = eligible;
      }
    }

    const test = runBacktest(candles15ByPair, { ...baseCfg, params: bestParams, tradeFrom: w.testFrom, tradeTo: w.testTo });
    const testMetrics = computeMetrics(test.trades, test.equityCurve, baseCfg.startCapital);
    results.push({
      window: w, bestParams, trainMetrics: bestMetrics!, testMetrics,
      testTrades: test.trades, testEquityCurve: test.equityCurve,
    });
    onProgress?.(
      `Fenster ${wi + 1}/${windows.length}: Train-PF ${bestMetrics!.profitFactor.toFixed(2)} ` +
      `(${JSON.stringify(bestParams)}) → Test-PF ${testMetrics.profitFactor.toFixed(2)} bei ${testMetrics.trades} Trades`,
    );
  }

  // OOS-Aggregat: Trades kombiniert, Equity-Kurven multiplikativ verkettet
  const oosTrades = results.flatMap((r) => r.testTrades);
  const oosEquityCurve: EquityPoint[] = [];
  let scale = 1;
  for (const r of results) {
    for (const p of r.testEquityCurve) {
      oosEquityCurve.push({ ts: p.ts, equity: baseCfg.startCapital * scale * (p.equity / baseCfg.startCapital) });
    }
    const last = r.testEquityCurve.at(-1);
    if (last) scale *= last.equity / baseCfg.startCapital;
  }
  const oosMetrics = computeMetrics(oosTrades, oosEquityCurve, baseCfg.startCapital);

  const worst = pickWorstEligibleWindow(results.map((r) => r.testMetrics));
  const finiteTrainPfs = results.map((r) => Math.min(r.trainMetrics.profitFactor, 10)); // Infinity kappen
  const avgTrainPf = finiteTrainPfs.reduce((s, v) => s + v, 0) / Math.max(1, finiteTrainPfs.length);

  const gate = evaluateGate({
    oosProfitFactor: oosMetrics.profitFactor,
    oosTrades: oosMetrics.trades,
    oosMaxDrawdownPct: oosMetrics.maxDrawdownPct,
    worstWindow: worst,
    avgTrainPf,
  });

  return { windows: results, oosMetrics, oosEquityCurve, gate };
}