import React, { useState, useMemo, useCallback, useRef } from 'react';
import * as XLSX from 'xlsx';

const MONTHS = ['January','February','March','April','May','June','July','August','September','October','November','December'];
const MONTHS_SHORT = ['Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'];

// Column indices of "Budget Units" in Budget 26 file (one per month, every 8 columns starting at 8)
const BUDGET_UNITS_COLS = [8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96];

interface SellInRow {
  sku: string;
  description: string;
  actualUnits: number;
  sellInBudget: number;
}

interface BudgetRow {
  sku: string;
  description: string;
  monthlyBudget: number[]; // 12 values Jan–Dec
}

interface ComparisonRow {
  sku: string;
  description: string;
  actualUnits: number;
  periodForecast: number;
  budgetYearTotal: number;
  budgetDiscrepancy: boolean;
  pctPeriod: number;
  pctAnnual: number;
}

function parseSellIn(buffer: ArrayBuffer): Map<string, SellInRow> {
  const wb = XLSX.read(buffer, { type: 'array' });
  const ws = wb.Sheets['Export'];
  if (!ws) throw new Error('Hoja "Export" no encontrada en fichero Sell in');
  const rows = XLSX.utils.sheet_to_json<any[]>(ws, { header: 1, defval: '' });
  const result = new Map<string, SellInRow>();
  for (let i = 1; i < rows.length; i++) {
    const row = rows[i];
    const rawArticle = String(row[0] ?? '').trim();
    if (!rawArticle) continue;
    const sku = rawArticle.slice(0, 5);
    if (!/^\d{5}$/.test(sku)) continue;
    result.set(sku, {
      sku,
      description: rawArticle.slice(6).trim(),
      actualUnits: Number(row[8]) || 0,
      sellInBudget: Number(row[10]) || 0,
    });
  }
  return result;
}

function parseBudget(buffer: ArrayBuffer): Map<string, BudgetRow> {
  const wb = XLSX.read(buffer, { type: 'array' });
  const ws = wb.Sheets['Export'];
  if (!ws) throw new Error('Hoja "Export" no encontrada en fichero Budget');
  const rows = XLSX.utils.sheet_to_json<any[]>(ws, { header: 1, defval: '' });
  const result = new Map<string, BudgetRow>();
  // Row 0 = months, Row 1 = sub-fields, data from row 2
  for (let i = 2; i < rows.length; i++) {
    const row = rows[i];
    const rawArticle = String(row[0] ?? '').trim();
    if (!rawArticle) continue;
    const sku = rawArticle.slice(0, 5);
    if (!/^\d{5}$/.test(sku)) continue;
    result.set(sku, {
      sku,
      description: rawArticle.slice(6).trim(),
      monthlyBudget: BUDGET_UNITS_COLS.map(c => Number(row[c]) || 0),
    });
  }
  return result;
}

const getPctColor = (pct: number) => {
  if (pct <= 0) return 'text-slate-500';
  if (pct >= 100) return 'text-emerald-400';
  if (pct >= 80) return 'text-amber-400';
  return 'text-rose-400';
};

const getPctBg = (pct: number) => {
  if (pct <= 0) return 'bg-slate-700';
  if (pct >= 100) return 'bg-emerald-500';
  if (pct >= 80) return 'bg-amber-400';
  return 'bg-rose-500';
};

// ── Sub-components ──────────────────────────────────────────────────────────

const DropZone: React.FC<{
  label: string;
  subtitle: string;
  loaded: boolean;
  fileName: string;
  count?: number;
  onDrop: (f: File) => void;
  onClick: () => void;
}> = ({ label, subtitle, loaded, fileName, count, onDrop, onClick }) => (
  <div
    className={`border-2 border-dashed rounded-xl p-6 flex flex-col items-center justify-center gap-3 cursor-pointer transition-all min-h-[140px] ${
      loaded
        ? 'border-emerald-500/50 bg-emerald-500/5'
        : 'border-slate-700 hover:border-indigo-500/50 hover:bg-indigo-500/5'
    }`}
    onClick={onClick}
    onDragOver={e => e.preventDefault()}
    onDrop={e => { e.preventDefault(); const f = e.dataTransfer.files[0]; if (f) onDrop(f); }}
  >
    <div className={`text-3xl ${loaded ? 'text-emerald-400' : 'text-slate-600'}`}>
      {loaded ? '✓' : '📊'}
    </div>
    <div className="text-center">
      <div className="text-sm font-black text-white">{label}</div>
      <div className="text-xs text-slate-500 mt-1">{subtitle}</div>
      {loaded
        ? <div className="text-xs text-emerald-400 mt-2">{fileName} — {count} SKUs cargados</div>
        : <div className="text-[10px] text-slate-600 mt-2 uppercase tracking-wider">Clic o arrastra aquí</div>
      }
    </div>
  </div>
);

const ComparisonTableRow: React.FC<{ row: ComparisonRow }> = React.memo(({ row }) => {
  const barWidth = Math.min(100, row.pctPeriod);
  return (
    <tr className="hover:bg-indigo-500/5 transition-colors border-b border-slate-800/50 last:border-0">
      <td className="px-4 py-3 whitespace-nowrap">
        <span className="text-xs font-black text-indigo-400 tracking-tighter">{row.sku}</span>
      </td>
      <td className="px-4 py-3 max-w-[280px]">
        <span className="text-sm text-slate-200 line-clamp-1" title={row.description}>
          {row.description}
        </span>
      </td>
      <td className="px-4 py-3 text-right whitespace-nowrap">
        <span className="text-sm font-black text-emerald-400">
          {row.actualUnits.toLocaleString('de-DE')}
        </span>
      </td>
      <td className="px-4 py-3 text-right whitespace-nowrap">
        <span className="text-sm font-bold text-slate-300">
          {row.periodForecast.toLocaleString('de-DE')}
        </span>
      </td>
      <td className="px-4 py-3 text-right whitespace-nowrap">
        <div className="flex flex-col items-end gap-0.5">
          <span className="text-sm font-bold text-slate-400">
            {row.budgetYearTotal.toLocaleString('de-DE')}
          </span>
          {row.budgetDiscrepancy && (
            <span className="text-[9px] font-black text-amber-400 uppercase">⚠ discrepancia</span>
          )}
        </div>
      </td>
      <td className="px-4 py-3">
        <div className="flex flex-col items-center gap-1">
          <span className={`text-sm font-black ${getPctColor(row.pctPeriod)}`}>
            {row.periodForecast > 0 ? `${row.pctPeriod.toFixed(1)}%` : '—'}
          </span>
          {row.periodForecast > 0 && (
            <div className="h-1.5 w-full bg-slate-800 rounded-full overflow-hidden max-w-[100px]">
              <div
                className={`h-full rounded-full ${getPctBg(row.pctPeriod)}`}
                style={{ width: `${barWidth}%` }}
              />
            </div>
          )}
        </div>
      </td>
      <td className="px-4 py-3 text-center whitespace-nowrap">
        <span className={`text-sm font-bold ${getPctColor(row.pctAnnual)}`}>
          {row.budgetYearTotal > 0 ? `${row.pctAnnual.toFixed(1)}%` : '—'}
        </span>
      </td>
    </tr>
  );
});

// ── Main Component ───────────────────────────────────────────────────────────

const ForecastView: React.FC = () => {
  const [sellInData, setSellInData] = useState<Map<string, SellInRow> | null>(null);
  const [budgetData, setBudgetData] = useState<Map<string, BudgetRow> | null>(null);
  const [sellInFileName, setSellInFileName] = useState('');
  const [budgetFileName, setBudgetFileName] = useState('');
  // Default cutoff: May (index 4) — adjust as needed
  const [cutoffMonth, setCutoffMonth] = useState<number>(4);
  const [sortAsc, setSortAsc] = useState(true);
  const [error, setError] = useState<string | null>(null);

  const sellInInputRef = useRef<HTMLInputElement>(null);
  const budgetInputRef = useRef<HTMLInputElement>(null);

  const loadFile = useCallback((file: File, type: 'sellin' | 'budget') => {
    setError(null);
    const reader = new FileReader();
    reader.onload = (e) => {
      try {
        const buf = e.target!.result as ArrayBuffer;
        if (type === 'sellin') {
          const data = parseSellIn(buf);
          setSellInData(data);
          setSellInFileName(file.name);
        } else {
          const data = parseBudget(buf);
          setBudgetData(data);
          setBudgetFileName(file.name);
        }
      } catch (err: any) {
        setError(`Error en ${type === 'sellin' ? 'Sell in' : 'Budget'}: ${err.message}`);
      }
    };
    reader.readAsArrayBuffer(file);
  }, []);

  const comparisonRows = useMemo((): ComparisonRow[] => {
    if (!budgetData) return [];
    const rows: ComparisonRow[] = [];
    budgetData.forEach((budgetRow) => {
      const sellIn = sellInData?.get(budgetRow.sku);
      const actualUnits = sellIn?.actualUnits ?? 0;
      const sellInBudget = sellIn?.sellInBudget ?? 0;
      const periodForecast = budgetRow.monthlyBudget
        .slice(0, cutoffMonth + 1)
        .reduce((a, b) => a + b, 0);
      const budgetYearTotal = budgetRow.monthlyBudget.reduce((a, b) => a + b, 0);
      const budgetDiscrepancy = sellIn != null && Math.abs(budgetYearTotal - sellInBudget) > 1;
      const pctPeriod = periodForecast > 0 ? (actualUnits / periodForecast) * 100 : 0;
      const pctAnnual = budgetYearTotal > 0 ? (actualUnits / budgetYearTotal) * 100 : 0;
      rows.push({
        sku: budgetRow.sku,
        description: budgetRow.description,
        actualUnits,
        periodForecast,
        budgetYearTotal,
        budgetDiscrepancy,
        pctPeriod,
        pctAnnual,
      });
    });
    rows.sort((a, b) => sortAsc ? a.pctPeriod - b.pctPeriod : b.pctPeriod - a.pctPeriod);
    return rows;
  }, [budgetData, sellInData, cutoffMonth, sortAsc]);

  const kpis = useMemo(() => {
    const totalActual = comparisonRows.reduce((s, r) => s + r.actualUnits, 0);
    const totalPeriodForecast = comparisonRows.reduce((s, r) => s + r.periodForecast, 0);
    const totalBudgetYear = comparisonRows.reduce((s, r) => s + r.budgetYearTotal, 0);
    const withForecast = comparisonRows.filter(r => r.periodForecast > 0);
    const below80 = withForecast.filter(r => r.pctPeriod < 80).length;
    const pctOverall = totalPeriodForecast > 0 ? (totalActual / totalPeriodForecast) * 100 : 0;
    return { totalActual, totalPeriodForecast, totalBudgetYear, below80, pctOverall, withForecastCount: withForecast.length };
  }, [comparisonRows]);

  const handleExport = useCallback(() => {
    const data = comparisonRows.map(r => ({
      SKU: r.sku,
      Descripción: r.description,
      'Real Sell-in (Uds)': r.actualUnits,
      [`Forecast Período Jan–${MONTHS_SHORT[cutoffMonth]}`]: r.periodForecast,
      'Budget Total Año': r.budgetYearTotal,
      'Discrepancia Budget': r.budgetDiscrepancy ? 'SÍ' : '',
      '% Cumpl. Período': r.periodForecast > 0 ? r.pctPeriod.toFixed(1) + '%' : '—',
      '% Budget Consumido': r.budgetYearTotal > 0 ? r.pctAnnual.toFixed(1) + '%' : '—',
    }));
    const ws = XLSX.utils.json_to_sheet(data);
    const wb = XLSX.utils.book_new();
    XLSX.utils.book_append_sheet(wb, ws, 'Sell-in vs Budget');
    XLSX.writeFile(wb, `SellIn_vs_Budget_${new Date().toISOString().slice(0, 10)}.xlsx`);
  }, [comparisonRows, cutoffMonth]);

  const isReady = budgetData !== null;

  return (
    <div className="flex flex-col gap-4 md:gap-6 animate-fade-in p-3 md:p-6 h-full overflow-hidden">
      {/* Hidden file inputs — always in DOM */}
      <input
        ref={sellInInputRef}
        type="file"
        accept=".xlsx,.xls"
        className="hidden"
        onChange={e => e.target.files?.[0] && loadFile(e.target.files[0], 'sellin')}
        onClick={e => { (e.target as HTMLInputElement).value = ''; }}
      />
      <input
        ref={budgetInputRef}
        type="file"
        accept=".xlsx,.xls"
        className="hidden"
        onChange={e => e.target.files?.[0] && loadFile(e.target.files[0], 'budget')}
        onClick={e => { (e.target as HTMLInputElement).value = ''; }}
      />

      {/* ── Upload UI (shown until budget is loaded) ── */}
      {!isReady && (
        <div className="bg-slate-900 border border-white/5 rounded-2xl p-6 flex flex-col gap-6">
          <h2 className="text-sm font-black text-white uppercase tracking-widest">
            Sell-in vs Budget 2026 — Carga los ficheros
          </h2>
          <div className="grid grid-cols-1 md:grid-cols-2 gap-4">
            <DropZone
              label="Sell in (*.xlsx)"
              subtitle="Col A: Raw Article · Col I: Sell-in Units Year · Col K: Budget Units"
              loaded={sellInData !== null}
              fileName={sellInFileName}
              count={sellInData?.size}
              onDrop={f => loadFile(f, 'sellin')}
              onClick={() => sellInInputRef.current?.click()}
            />
            <DropZone
              label="Budget 26 (*.xlsx)"
              subtitle="Hoja Export · Fila 1: meses · Fila 2: sub-campos · Datos desde fila 3"
              loaded={budgetData !== null}
              fileName={budgetFileName}
              count={budgetData?.size}
              onDrop={f => loadFile(f, 'budget')}
              onClick={() => budgetInputRef.current?.click()}
            />
          </div>
          {error && (
            <div className="p-3 bg-rose-500/10 border border-rose-500/20 rounded-lg text-xs text-rose-400">
              {error}
            </div>
          )}
        </div>
      )}

      {/* ── Compact toolbar (shown when budget is loaded) ── */}
      {isReady && (
        <div className="flex flex-wrap items-center gap-3 shrink-0">
          <button
            onClick={() => sellInInputRef.current?.click()}
            className={`flex items-center gap-2 px-3 py-1.5 rounded-lg border text-[10px] font-black uppercase tracking-wider transition-all ${
              sellInData
                ? 'border-emerald-500/30 bg-emerald-500/10 text-emerald-400'
                : 'border-slate-600 text-slate-400 hover:border-indigo-500/50'
            }`}
          >
            {sellInData ? '✓' : '+'} Sell In{sellInData ? ` (${sellInData.size} SKUs)` : ' — sin cargar'}
          </button>
          <button
            onClick={() => budgetInputRef.current?.click()}
            className="flex items-center gap-2 px-3 py-1.5 rounded-lg border text-[10px] font-black uppercase tracking-wider border-emerald-500/30 bg-emerald-500/10 text-emerald-400"
          >
            ✓ Budget 26 ({budgetData!.size} SKUs)
          </button>
          {error && <span className="text-xs text-rose-400">{error}</span>}

          <div className="flex items-center gap-2 ml-auto">
            <span className="text-[10px] font-black text-slate-400 uppercase tracking-wider">Período hasta</span>
            <select
              value={cutoffMonth}
              onChange={e => setCutoffMonth(Number(e.target.value))}
              className="bg-slate-800 border border-white/10 rounded-lg px-3 py-1.5 text-sm text-white focus:outline-none focus:ring-1 focus:ring-indigo-500"
            >
              {MONTHS.map((m, i) => <option key={m} value={i}>{m}</option>)}
            </select>
          </div>
          <button
            onClick={handleExport}
            className="px-3 py-1.5 bg-slate-800 hover:bg-slate-700 text-white rounded-lg border border-white/5 transition-all text-xs font-black uppercase tracking-wider"
            title="Exportar a Excel"
          >
            ↓ Excel
          </button>
        </div>
      )}

      {/* ── KPI Cards ── */}
      {isReady && (
        <div className="grid grid-cols-2 md:grid-cols-4 gap-3 shrink-0">
          <div className="bg-slate-900 border border-white/5 p-4 rounded-xl shadow-lg">
            <div className="text-[10px] font-black text-emerald-400 uppercase tracking-widest mb-1">Total Real</div>
            <div className="text-2xl font-black text-emerald-400">{kpis.totalActual.toLocaleString('de-DE')}</div>
            <div className="text-[9px] text-slate-500 mt-1 uppercase">Unidades vendidas a Amazon</div>
          </div>
          <div className="bg-slate-900 border border-white/5 p-4 rounded-xl shadow-lg">
            <div className="text-[10px] font-black text-indigo-400 uppercase tracking-widest mb-1">
              Forecast Jan–{MONTHS_SHORT[cutoffMonth]}
            </div>
            <div className="text-2xl font-black text-white">{kpis.totalPeriodForecast.toLocaleString('de-DE')}</div>
            <div className={`text-[11px] font-black mt-1 ${getPctColor(kpis.pctOverall)}`}>
              {kpis.pctOverall.toFixed(1)}% cumplimiento global
            </div>
          </div>
          <div className="bg-slate-900 border border-white/5 p-4 rounded-xl shadow-lg">
            <div className="text-[10px] font-black text-slate-400 uppercase tracking-widest mb-1">Budget Total Año</div>
            <div className="text-2xl font-black text-white">{kpis.totalBudgetYear.toLocaleString('de-DE')}</div>
            <div className="text-[9px] text-slate-500 mt-1 uppercase">12 meses acumulados</div>
          </div>
          <div className="bg-slate-900 border border-white/5 p-4 rounded-xl shadow-lg">
            <div className="text-[10px] font-black text-rose-400 uppercase tracking-widest mb-1">SKUs &lt; 80% Forecast</div>
            <div className="text-2xl font-black text-rose-400">{kpis.below80}</div>
            <div className="text-[9px] text-slate-500 mt-1 uppercase">
              de {kpis.withForecastCount} con forecast período
            </div>
          </div>
        </div>
      )}

      {/* ── Comparison Table ── */}
      {isReady && (
        <div className="bg-slate-900 border border-white/10 rounded-2xl overflow-hidden shadow-2xl flex-1 flex flex-col min-h-0">
          <div className="flex-1 overflow-auto min-h-0 custom-scrollbar">
            <table className="w-full text-left border-collapse text-xs md:text-sm">
              <thead className="sticky top-0 z-20 bg-slate-950 shadow-sm">
                <tr className="text-[10px] font-black text-slate-500 uppercase tracking-wider">
                  <th className="px-4 py-3 text-left w-[7%]">SKU</th>
                  <th className="px-4 py-3 text-left">Descripción</th>
                  <th className="px-4 py-3 text-right w-[11%]">Real Sell-in</th>
                  <th className="px-4 py-3 text-right w-[13%]">
                    Forecast Período
                    <div className="text-[9px] font-normal normal-case text-slate-600 mt-0.5">
                      Jan–{MONTHS_SHORT[cutoffMonth]}
                    </div>
                  </th>
                  <th className="px-4 py-3 text-right w-[11%]">
                    Budget Año
                    <div className="text-[9px] font-normal normal-case text-slate-600 mt-0.5">12 meses</div>
                  </th>
                  <th
                    className="px-4 py-3 text-center w-[15%] cursor-pointer hover:text-white select-none"
                    onClick={() => setSortAsc(prev => !prev)}
                  >
                    % Cumpl. Período {sortAsc ? '↑' : '↓'}
                    <div className="text-[9px] font-normal normal-case text-slate-600 mt-0.5">real / forecast período</div>
                  </th>
                  <th className="px-4 py-3 text-center w-[13%]">
                    % Budget Consumido
                    <div className="text-[9px] font-normal normal-case text-slate-600 mt-0.5">real / budget año</div>
                  </th>
                </tr>
              </thead>
              <tbody className="divide-y divide-slate-800/50">
                {comparisonRows.map(row => (
                  <ComparisonTableRow key={row.sku} row={row} />
                ))}
              </tbody>
            </table>
            {comparisonRows.length === 0 && (
              <div className="flex items-center justify-center py-20 text-slate-500 text-sm">
                Sin datos de comparación
              </div>
            )}
          </div>
        </div>
      )}
    </div>
  );
};

export default ForecastView;