import React, { useEffect, useMemo, useState } from 'react';
import {
  BarChart,
  Bar,
  XAxis,
  YAxis,
  Tooltip,
  ResponsiveContainer,
  Legend,
} from 'recharts';
import { format } from 'date-fns';
import { fetchMonthlyKpi, type MonthlyKPI } from '@/app/utils/api';

interface MonthlyBarChartProps {
  siteId: string;
}

const getLastNMonthKeys = (n: number): string[] => {
  const out: string[] = [];
  const now = new Date();
  // include current month, go back n-1 months
  for (let i = 0; i < n; i++) {
    const d = new Date(now.getFullYear(), now.getMonth() - (n - 1 - i), 1);
    const key = `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, '0')}`; // YYYY-MM
    out.push(key);
  }
  return out;
};

function useIsDarkMode() {
  const [isDark, setIsDark] = useState(() =>
    typeof document !== 'undefined'
      ? document.body.classList.contains('dark')
      : false
  );

  useEffect(() => {
    const check = () => setIsDark(document.body.classList.contains('dark'));
    check();
    const observer = new MutationObserver(check);
    observer.observe(document.body, { attributes: true, attributeFilter: ['class'] });
    return () => observer.disconnect();
  }, []);

  return isDark;
}

const MonthlyBarChart: React.FC<MonthlyBarChartProps> = ({ siteId }) => {
  const [chartData, setChartData] = useState<
    { month: string; consumption: number; generation: number }[]
  >([]);
  const [loading, setLoading] = useState(true);

  const isDark = useIsDarkMode();
  const consumptionColor = isDark ? '#ba8e23' : '#003049';
  const generationColor = isDark ? '#fcd913' : '#669bbc';

  const monthKeys = useMemo(() => getLastNMonthKeys(6), []);

  useEffect(() => {
    if (!siteId) return;

    const load = async () => {
      setLoading(true);
      try {
        // Fetch all 6 months in parallel
        const results: MonthlyKPI[] = await Promise.all(
          monthKeys.map((month) =>
            fetchMonthlyKpi({
              site: siteId,
              month,
              // consumption_topic: '...', // optional if your API needs it
              // generation_topic: '...',  // optional if your API needs it
            }).catch((e) => {
              // normalize failures to an error-shaped record so the chart can still render other months
              return {
                site: siteId,
                month,
                yield_kwh: null,
                consumption_kwh: null,
                grid_draw_kwh: null,
                efficiency: null,
                peak_demand_kw: null,
                avg_power_factor: null,
                load_factor: null,
                error: String(e),
              } as MonthlyKPI;
            })
          )
        );

        // Map to chart rows; default nulls to 0 for stacking/tooltip friendliness
        const rows = results.map((kpi) => {
          const monthLabel = format(new Date(`${kpi.month}-01`), 'MMM');
          return {
            month: monthLabel,
            consumption: kpi.consumption_kwh ?? 0,
            generation: kpi.yield_kwh ?? 0,
          };
        });

        setChartData(rows);
      } finally {
        setLoading(false);
      }
    };

    load();
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [siteId]); // monthKeys are stable via useMemo

  if (loading || !siteId || chartData.length === 0) {
    return (
      <div className="bg-white p-3 rounded-lg shadow-md dark:bg-rtgray-800 dark:text-white-light">
        <div className="h-[200px] w-full flex items-center justify-center">
          <p className="text-white/70">
            {loading ? 'Loading data...' : 'No data available for chart.'}
          </p>
        </div>
      </div>
    );
  }

  return (
    <div className="bg-white p-3 rounded-lg dark:bg-rtgray-800 dark:text-white-light">
      <div className="h-[200px] w-full">
        <ResponsiveContainer width="100%" height="100%">
          <BarChart data={chartData}>
            <XAxis
              dataKey="month"
              tick={{ fontSize: 10, fill: isDark ? '#fff' : '#222' }}
              axisLine={{ stroke: isDark ? '#fff' : '#222' }}
              tickLine={{ stroke: isDark ? '#fff' : '#222' }}
            />
            <YAxis
              tick={{ fontSize: 10, fill: isDark ? '#fff' : '#222' }}
              axisLine={{ stroke: isDark ? '#fff' : '#222' }}
              tickLine={{ stroke: isDark ? '#fff' : '#222' }}
              label={{
                value: 'Energy (kWh)', // fixed: units are kWh
                angle: -90,
                position: 'insideLeft',
                style: {
                  textAnchor: 'middle',
                  fill: isDark ? '#fff' : '#222',
                  fontSize: 12,
                },
              }}
            />
            <Tooltip
              formatter={(value: number) => [`${value.toFixed(2)} kWh`]}
              labelFormatter={(label) => `${label}`}
              contentStyle={{
                background: isDark ? '#232b3e' : '#fff',
                color: isDark ? '#fff' : '#222',
                border: isDark ? '1px solid #444' : '1px solid #ccc',
              }}
              labelStyle={{
                color: isDark ? '#fff' : '#222',
              }}
              cursor={{
                fill: isDark ? '#808080' : '#e0e7ef',
                fillOpacity: isDark ? 0.6 : 0.3,
              }}
            />
            <Legend wrapperStyle={{ color: isDark ? '#fff' : '#222' }} />
            <Bar dataKey="consumption" fill={consumptionColor} name="Consumption (kWh)" />
            <Bar dataKey="generation" fill={generationColor} name="Generation (kWh)" />
          </BarChart>
        </ResponsiveContainer>
      </div>
    </div>
  );
};

export default MonthlyBarChart;