export const config = { runtime: 'edge' };

import { getCorsHeaders, isDisallowedOrigin } from './_cors.js';

const CACHE_TTL = 900;
let cachedResponse = null;
let cacheTimestamp = 0;

const ETF_LIST = [
  { ticker: 'IBIT', issuer: 'BlackRock' },
  { ticker: 'FBTC', issuer: 'Fidelity' },
  { ticker: 'ARKB', issuer: 'ARK/21Shares' },
  { ticker: 'BITB', issuer: 'Bitwise' },
  { ticker: 'GBTC', issuer: 'Grayscale' },
  { ticker: 'HODL', issuer: 'VanEck' },
  { ticker: 'BRRR', issuer: 'Valkyrie' },
  { ticker: 'EZBC', issuer: 'Franklin' },
  { ticker: 'BTCO', issuer: 'Invesco' },
  { ticker: 'BTCW', issuer: 'WisdomTree' },
];

async function fetchChart(ticker) {
  const url = `https://query1.finance.yahoo.com/v8/finance/chart/${ticker}?range=5d&interval=1d`;
  const controller = new AbortController();
  const id = setTimeout(() => controller.abort(), 8000);
  try {
    const res = await fetch(url, { signal: controller.signal });
    if (!res.ok) return null;
    return await res.json();
  } catch {
    return null;
  } finally {
    clearTimeout(id);
  }
}

function parseChartData(chart, ticker, issuer) {
  try {
    const result = chart?.chart?.result?.[0];
    if (!result) return null;

    const quote = result.indicators?.quote?.[0];
    const closes = quote?.close || [];
    const volumes = quote?.volume || [];

    const validCloses = closes.filter(p => p != null);
    const validVolumes = volumes.filter(v => v != null);

    if (validCloses.length < 2) return null;

    const latestPrice = validCloses[validCloses.length - 1];
    const prevPrice = validCloses[validCloses.length - 2];
    const priceChange = prevPrice ? ((latestPrice - prevPrice) / prevPrice * 100) : 0;

    const latestVolume = validVolumes.length > 0 ? validVolumes[validVolumes.length - 1] : 0;
    const avgVolume = validVolumes.length > 1
      ? validVolumes.slice(0, -1).reduce((a, b) => a + b, 0) / (validVolumes.length - 1)
      : latestVolume;

    // Estimate flow direction from price change + volume
    const volumeRatio = avgVolume > 0 ? latestVolume / avgVolume : 1;
    const direction = priceChange > 0.1 ? 'inflow' : priceChange < -0.1 ? 'outflow' : 'neutral';
    const estFlowMagnitude = latestVolume * latestPrice * (priceChange > 0 ? 1 : -1) * 0.1;

    return {
      ticker,
      issuer,
      price: +latestPrice.toFixed(2),
      priceChange: +priceChange.toFixed(2),
      volume: latestVolume,
      avgVolume: Math.round(avgVolume),
      volumeRatio: +volumeRatio.toFixed(2),
      direction,
      estFlow: Math.round(estFlowMagnitude),
    };
  } catch {
    return null;
  }
}

function buildFallbackResult() {
  return {
    timestamp: new Date().toISOString(),
    summary: {
      etfCount: 0,
      totalVolume: 0,
      totalEstFlow: 0,
      netDirection: 'UNAVAILABLE',
      inflowCount: 0,
      outflowCount: 0,
    },
    etfs: [],
    unavailable: true,
  };
}

export default async function handler(req) {
  const cors = getCorsHeaders(req);
  if (req.method === 'OPTIONS') {
    if (isDisallowedOrigin(req)) {
      return new Response(null, { status: 403, headers: cors });
    }
    return new Response(null, { status: 204, headers: cors });
  }
  if (isDisallowedOrigin(req)) {
    return new Response(JSON.stringify({ error: 'Forbidden' }), { status: 403, headers: { ...cors, 'Content-Type': 'application/json' } });
  }

  const now = Date.now();
  if (cachedResponse && now - cacheTimestamp < CACHE_TTL * 1000) {
    return new Response(JSON.stringify(cachedResponse), {
      headers: { ...cors, 'Content-Type': 'application/json', 'Cache-Control': `public, s-maxage=${CACHE_TTL}, stale-while-revalidate=1800` },
    });
  }

  try {
    const charts = await Promise.allSettled(
      ETF_LIST.map(etf => fetchChart(etf.ticker))
    );

    const etfs = [];
    for (let i = 0; i < ETF_LIST.length; i++) {
      const chart = charts[i].status === 'fulfilled' ? charts[i].value : null;
      if (chart) {
        const parsed = parseChartData(chart, ETF_LIST[i].ticker, ETF_LIST[i].issuer);
        if (parsed) etfs.push(parsed);
      }
    }

    const totalVolume = etfs.reduce((sum, e) => sum + e.volume, 0);
    const totalEstFlow = etfs.reduce((sum, e) => sum + e.estFlow, 0);
    const inflowCount = etfs.filter(e => e.direction === 'inflow').length;
    const outflowCount = etfs.filter(e => e.direction === 'outflow').length;

    const result = {
      timestamp: new Date().toISOString(),
      summary: {
        etfCount: etfs.length,
        totalVolume,
        totalEstFlow,
        netDirection: totalEstFlow > 0 ? 'NET INFLOW' : totalEstFlow < 0 ? 'NET OUTFLOW' : 'NEUTRAL',
        inflowCount,
        outflowCount,
      },
      etfs: etfs.sort((a, b) => b.volume - a.volume),
    };

    cachedResponse = result;
    cacheTimestamp = now;

    return new Response(JSON.stringify(result), {
      headers: { ...cors, 'Content-Type': 'application/json', 'Cache-Control': `public, s-maxage=${CACHE_TTL}, stale-while-revalidate=1800` },
    });
  } catch (err) {
    const fallback = cachedResponse || buildFallbackResult();
    cachedResponse = fallback;
    cacheTimestamp = now;
    return new Response(JSON.stringify(fallback), {
      status: 200,
      headers: { ...cors, 'Content-Type': 'application/json', 'Cache-Control': 'public, max-age=30, s-maxage=60, stale-while-revalidate=30' },
    });
  }
}