import { useState, useEffect, useCallback } from "react";
import { Link } from "react-router";
import type { MostActiveStock } from "../types";

function formatVolume(vol: number): string {
  if (vol >= 1_000_000_000) return `${(vol / 1_000_000_000).toFixed(1)}B`;
  if (vol >= 1_000_000) return `${(vol / 1_000_000).toFixed(1)}M`;
  if (vol >= 1_000) return `${(vol / 1_000).toFixed(1)}K`;
  return vol.toString();
}

function formatPrice(price: number): string {
  return `$${price.toFixed(2)}`;
}

function formatChangePercent(pct: number): string {
  return `${pct >= 0 ? "+" : ""}${pct.toFixed(2)}%`;
}

export default function MostActiveStocks() {
  const [stocks, setStocks] = useState<MostActiveStock[]>([]);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState<string | null>(null);

  const fetchData = useCallback(async () => {
    try {
      setError(null);
      const res = await fetch("/api/stocks/most-actives");
      if (!res.ok) {
        const data = await res.json();
        throw new Error(data.error || "Failed to fetch data");
      }
      const data = await res.json();
      setStocks(data);
    } catch (err) {
      const message = err instanceof Error ? err.message : "Failed to fetch most active stocks.";
      setError(message);
    } finally {
      setLoading(false);
    }
  }, []);

  useEffect(() => {
    fetchData();
    const interval = setInterval(fetchData, 30000);
    return () => clearInterval(interval);
  }, [fetchData]);

  if (loading) {
    return (
      <div className="bg-white rounded-xl shadow-lg p-6 border border-gray-200">
        <div className="space-y-3">
          {Array.from({ length: 8 }).map((_, i) => (
            <div key={i} className="animate-pulse flex gap-4 py-3 border-b border-gray-100 last:border-0">
              <div className="h-5 bg-gray-200 rounded w-16" />
              <div className="h-5 bg-gray-200 rounded w-32" />
              <div className="h-5 bg-gray-200 rounded w-20" />
              <div className="h-5 bg-gray-200 rounded w-20" />
              <div className="h-5 bg-gray-200 rounded w-24" />
            </div>
          ))}
        </div>
      </div>
    );
  }

  if (error && stocks.length === 0) {
    return (
      <div className="bg-white rounded-xl shadow-lg p-6 border border-gray-200">
        <div className="bg-red-50 border border-red-200 rounded-lg p-4">
          <p className="text-red-600 text-sm mb-3">{error}</p>
          <button
            onClick={fetchData}
            className="bg-blue-600 text-white px-4 py-2 rounded-lg text-sm font-medium hover:bg-blue-700 transition-colors"
          >
            Retry
          </button>
        </div>
      </div>
    );
  }

  return (
    <div className="bg-white rounded-xl shadow-lg border border-gray-200 overflow-hidden">
      {error && (
        <div className="bg-red-50 border-b border-red-200 px-6 py-3">
          <p className="text-red-600 text-sm">{error}</p>
        </div>
      )}
      <div className="overflow-x-auto">
        <table className="w-full">
          <thead>
            <tr className="bg-gray-50 border-b border-gray-200">
              <th className="text-left px-6 py-4 text-sm font-semibold text-gray-600">Symbol</th>
              <th className="text-left px-6 py-4 text-sm font-semibold text-gray-600">Name</th>
              <th className="text-right px-6 py-4 text-sm font-semibold text-gray-600">Price</th>
              <th className="text-right px-6 py-4 text-sm font-semibold text-gray-600">Change %</th>
              <th className="text-right px-6 py-4 text-sm font-semibold text-gray-600">Volume</th>
            </tr>
          </thead>
          <tbody>
            {stocks.map((stock) => (
              <tr key={stock.symbol} className="border-b border-gray-100 hover:bg-gray-50 transition-colors">
                <td className="px-6 py-4">
                  <Link
                    to={`/analyze/${stock.symbol}`}
                    className="text-blue-600 font-semibold hover:text-blue-700 hover:underline"
                  >
                    {stock.symbol}
                  </Link>
                </td>
                <td className="px-6 py-4 text-gray-600">{stock.name}</td>
                <td className="px-6 py-4 text-right font-mono text-gray-900">{formatPrice(stock.price)}</td>
                <td className={`px-6 py-4 text-right font-mono font-medium ${stock.changePercent >= 0 ? "text-green-600" : "text-red-600"}`}>
                  {formatChangePercent(stock.changePercent)}
                </td>
                <td className="px-6 py-4 text-right text-gray-600">{formatVolume(stock.volume)}</td>
              </tr>
            ))}
          </tbody>
        </table>
      </div>
    </div>
  );
}