import { NextResponse } from 'next/server';

export const dynamic = 'force-dynamic';

interface WhaleFilingDate {
  date: string;
}

interface WhaleHoldingRaw {
  symbol: string;
  securityName: string;
  shares: number;
  value: number;
  date: string;
}

interface WhaleProfile {
  name: string;
  cik: string;
  aum: number;
  holdingsCount: number;
  topSector: string;
  filingDate: string;
}

interface PositionDelta {
  manager: string;
  symbol: string;
  name: string;
  currentWeight: number;
  prevWeight: number;
  vocDelta: number;
  shares: number;
  value: number;
}

// target tracking CIK registry
const TARGET_WHALES = [
  { name: 'Scion Asset Management (Michael Burry)', cik: '0001649339', sector: 'Consumer Cyclical' },
  { name: 'Akre Capital Management (Chuck Akre)', cik: '0001483348', sector: 'Financial Services' },
  { name: 'Mairs & Power Small Cap Fund', cik: '0001099684', sector: 'Industrials' }
];

// Offline high-fidelity mock data baseline
const MOCK_WHALE_PROFILES: WhaleProfile[] = [
  {
    name: 'Scion Asset Management (Michael Burry)',
    cik: '0001649339',
    aum: 118420000,
    holdingsCount: 16,
    topSector: 'Consumer Cyclical',
    filingDate: '2026-05-15'
  },
  {
    name: 'Akre Capital Management (Chuck Akre)',
    cik: '0001483348',
    aum: 13420800000,
    holdingsCount: 22,
    topSector: 'Financial Services',
    filingDate: '2026-05-15'
  },
  {
    name: 'Mairs & Power Small Cap Fund',
    cik: '0001099684',
    aum: 928400000,
    holdingsCount: 38,
    topSector: 'Industrials',
    filingDate: '2026-05-14'
  }
];

const MOCK_WHALE_POSITIONS: PositionDelta[] = [
  {
    manager: 'Scion Asset Management (Michael Burry)',
    symbol: 'JD',
    name: 'JD.com Inc. ADR',
    currentWeight: 10.45,
    prevWeight: 5.21,
    vocDelta: 5.24,
    shares: 280000,
    value: 12373000
  },
  {
    manager: 'Scion Asset Management (Michael Burry)',
    symbol: 'BABA',
    name: 'Alibaba Group Holding Ltd.',
    currentWeight: 9.82,
    prevWeight: 6.12,
    vocDelta: 3.70,
    shares: 135000,
    value: 11629000
  },
  {
    manager: 'Mairs & Power Small Cap Fund',
    symbol: 'TNC',
    name: 'Tennant Company',
    currentWeight: 5.42,
    prevWeight: 2.15,
    vocDelta: 3.27,
    shares: 480000,
    value: 50320000
  },
  {
    manager: 'Akre Capital Management (Chuck Akre)',
    symbol: 'MA',
    name: 'Mastercard Inc.',
    currentWeight: 16.85,
    prevWeight: 13.80,
    vocDelta: 3.05,
    shares: 5100000,
    value: 2261470000
  },
  {
    manager: 'Scion Asset Management (Michael Burry)',
    symbol: 'BIDU',
    name: 'Baidu Inc. ADR',
    currentWeight: 5.82,
    prevWeight: 3.55,
    vocDelta: 2.27,
    shares: 65000,
    value: 6891000
  },
  {
    manager: 'Akre Capital Management (Chuck Akre)',
    symbol: 'V',
    name: 'Visa Inc.',
    currentWeight: 14.12,
    prevWeight: 12.15,
    vocDelta: 1.97,
    shares: 6800000,
    value: 1895020000
  },
  {
    manager: 'Mairs & Power Small Cap Fund',
    symbol: 'HURC',
    name: 'Hurco Companies Inc.',
    currentWeight: 3.85,
    prevWeight: 2.10,
    vocDelta: 1.75,
    shares: 1400000,
    value: 35742000
  },
  {
    manager: 'Akre Capital Management (Chuck Akre)',
    symbol: 'KMX',
    name: 'CarMax Inc.',
    currentWeight: 7.95,
    prevWeight: 6.80,
    vocDelta: 1.15,
    shares: 11200000,
    value: 1066980000
  },
  {
    manager: 'Scion Asset Management (Michael Burry)',
    symbol: 'BP',
    name: 'BP plc ADR',
    currentWeight: 3.25,
    prevWeight: 4.55,
    vocDelta: -1.30,
    shares: 105000,
    value: 3848000
  },
  {
    manager: 'Mairs & Power Small Cap Fund',
    symbol: 'CSGP',
    name: 'CoStar Group Inc.',
    currentWeight: 1.12,
    prevWeight: 2.85,
    vocDelta: -1.73,
    shares: 150000,
    value: 10398000
  },
  {
    manager: 'Scion Asset Management (Michael Burry)',
    symbol: 'GOOGL',
    name: 'Alphabet Inc.',
    currentWeight: 0.00,
    prevWeight: 5.12,
    vocDelta: -5.12,
    shares: 0,
    value: 0
  }
];

async function fetchWithTimeout(url: string, timeoutMs = 4000): Promise<Response> {
  const controller = new AbortController();
  const id = setTimeout(() => controller.abort(), timeoutMs);
  try {
    const response = await fetch(url, { signal: controller.signal, cache: 'no-store' });
    clearTimeout(id);
    return response;
  } catch (err) {
    clearTimeout(id);
    throw err;
  }
}

export async function GET() {
  const isDevMode = process.env.DEV_MODE === 'true';
  const apiKey = process.env.FMP_API_KEY || 'U6lOXaOFPye7oc1D235kyAqJeQaiTAWc';
  const now = Date.now();

  // 1. DEV_MODE Interception check
  if (isDevMode) {
    const response = NextResponse.json({
      whales: MOCK_WHALE_PROFILES,
      positions: MOCK_WHALE_POSITIONS,
      isShieldActive: true,
      timestamp: now
    });
    response.headers.set('Cache-Control', 'no-store, max-age=0, must-revalidate');
    response.headers.set('X-Shield-Active', 'true');
    return response;
  }

  // 2. Live FMP Ingestion
  try {
    const whaleProfiles: WhaleProfile[] = [];
    const positionsList: PositionDelta[] = [];

    for (const target of TARGET_WHALES) {
      // Step A: Fetch Filing Dates
      const datesUrl = `https://financialmodelingprep.com/api/v3/form-thirteen-date/${target.cik}?apikey=${apiKey}`;
      const datesRes = await fetchWithTimeout(datesUrl);
      if (!datesRes.ok) {
        throw new Error(`Failed to fetch dates for CIK ${target.cik}`);
      }
      const dates: WhaleFilingDate[] = await datesRes.json();

      if (!Array.isArray(dates) || dates.length < 2) {
        // Fallback to mock profiles/positions for this specific whale if insufficient historical filings exist
        const mockProfile = MOCK_WHALE_PROFILES.find(p => p.cik === target.cik);
        if (mockProfile) {
          whaleProfiles.push(mockProfile);
          MOCK_WHALE_POSITIONS.filter(pos => pos.manager.includes(target.name)).forEach(pos => {
            positionsList.push(pos);
          });
        }
        continue;
      }

      const dateCurrent = dates[0].date;
      const datePrevious = dates[1].date;

      // Step B: Fetch Holdings for Current & Previous quarters
      const currentUrl = `https://financialmodelingprep.com/api/v3/form-thirteen/${target.cik}?date=${dateCurrent}&apikey=${apiKey}`;
      const prevUrl = `https://financialmodelingprep.com/api/v3/form-thirteen/${target.cik}?date=${datePrevious}&apikey=${apiKey}`;

      const [currRes, prevRes] = await Promise.all([
        fetchWithTimeout(currentUrl),
        fetchWithTimeout(prevUrl)
      ]);

      if (!currRes.ok || !prevRes.ok) {
        throw new Error(`Failed to fetch holdings data for CIK ${target.cik}`);
      }

      const rawCurrent: WhaleHoldingRaw[] = await currRes.json();
      const rawPrevious: WhaleHoldingRaw[] = await prevRes.json();

      // Step C: Compute total filing values (AUM)
      const currentAum = rawCurrent.reduce((acc, item) => acc + (item.value || 0), 0);
      const prevAum = rawPrevious.reduce((acc, item) => acc + (item.value || 0), 0);

      whaleProfiles.push({
        name: target.name,
        cik: target.cik,
        aum: currentAum,
        holdingsCount: rawCurrent.length,
        topSector: target.sector,
        filingDate: dateCurrent
      });

      // Step D: Calculate delta weights
      const prevHoldingsMap = new Map<string, WhaleHoldingRaw>();
      rawPrevious.forEach(h => {
        if (h.symbol) {
          prevHoldingsMap.set(h.symbol, h);
        }
      });

      const processedSymbols = new Set<string>();

      // Process current holdings
      rawCurrent.forEach(curr => {
        if (!curr.symbol) return;
        processedSymbols.add(curr.symbol);

        const prev = prevHoldingsMap.get(curr.symbol);

        const currentWeight = currentAum > 0 ? (curr.value / currentAum) * 100 : 0;
        const prevWeight = prev && prevAum > 0 ? (prev.value / prevAum) * 100 : 0;
        const vocDelta = currentWeight - prevWeight;

        positionsList.push({
          manager: target.name,
          symbol: curr.symbol,
          name: curr.securityName || `${curr.symbol} Corp.`,
          currentWeight: parseFloat(currentWeight.toFixed(2)),
          prevWeight: parseFloat(prevWeight.toFixed(2)),
          vocDelta: parseFloat(vocDelta.toFixed(2)),
          shares: curr.shares,
          value: curr.value
        });
      });

      // Process closed out positions (held in previous quarter, but not current)
      rawPrevious.forEach(prev => {
        if (!prev.symbol || processedSymbols.has(prev.symbol)) return;

        const prevWeight = prevAum > 0 ? (prev.value / prevAum) * 100 : 0;
        const vocDelta = 0 - prevWeight;

        positionsList.push({
          manager: target.name,
          symbol: prev.symbol,
          name: prev.securityName || `${prev.symbol} Corp.`,
          currentWeight: 0,
          prevWeight: parseFloat(prevWeight.toFixed(2)),
          vocDelta: parseFloat(vocDelta.toFixed(2)),
          shares: 0,
          value: 0
        });
      });
    }

    // Sort positions by delta weight descending
    positionsList.sort((a, b) => b.vocDelta - a.vocDelta);

    return NextResponse.json({
      whales: whaleProfiles,
      positions: positionsList,
      isShieldActive: false,
      timestamp: now
    });
  } catch (err: any) {
    console.error("FMP Ingestion for Whale Screener failed, falling back to mock archive. Reason:", err.message || err);
    // Fallback response on error
    const response = NextResponse.json({
      whales: MOCK_WHALE_PROFILES,
      positions: MOCK_WHALE_POSITIONS,
      isShieldActive: true,
      timestamp: now
    });
    response.headers.set('Cache-Control', 'no-store, max-age=0, must-revalidate');
    return response;
  }
}