import { useState, useEffect, useCallback, useRef } from 'react';
import api from '../api/client';
import { useAuth } from '../contexts/AuthContext';
import WeekNavigator, { getWeekRange } from '../components/WeekNavigator';
import DayCard from '../components/DayCard';
import SaveIndicator from '../components/SaveIndicator';
import StatusBadge from '../components/StatusBadge';
import { Send, Download, Mail, Loader2, Copy, TrendingUp } from 'lucide-react';

function toLocalDateStr(d) {
  // Format as YYYY-MM-DD in local timezone (avoid UTC shift)
  const y = d.getFullYear();
  const m = String(d.getMonth() + 1).padStart(2, '0');
  const day = String(d.getDate()).padStart(2, '0');
  return `${y}-${m}-${day}`;
}

function getWeekDates(date) {
  const { start } = getWeekRange(date);
  const dates = [];
  for (let i = 0; i < 7; i++) {
    const d = new Date(start);
    d.setDate(start.getDate() + i);
    dates.push(toLocalDateStr(d));
  }
  return dates;
}

function formatWeekParam(date) {
  const { start } = getWeekRange(date);
  return toLocalDateStr(start);
}

export default function Timesheet() {
  const { user } = useAuth();
  const [selectedDate, setSelectedDate] = useState(new Date());
  const [entries, setEntries] = useState({});
  const [homeowners, setHomeowners] = useState([]);
  const [timesheet, setTimesheet] = useState(null);
  const [saveStatus, setSaveStatus] = useState('saved');
  const [loading, setLoading] = useState(true);
  const [submitting, setSubmitting] = useState(false);
  const [pdfLoading, setPdfLoading] = useState(false);
  const [copying, setCopying] = useState(false);
  const [overtime, setOvertime] = useState(null);
  const saveTimer = useRef(null);
  const pendingChanges = useRef({});

  const weekDates = getWeekDates(selectedDate);
  const weekParam = formatWeekParam(selectedDate);
  // rejected timesheets can be edited and resubmitted
  const timesheetId = timesheet?.id || timesheet?.timesheetId;
  const isLocked = timesheet?.status === 'submitted' || timesheet?.status === 'approved';

  // Load data for current week
  const loadWeek = useCallback(async () => {
    setLoading(true);
    try {
      const [entriesRes, timesheetRes, homeownersRes] = await Promise.all([
        api.get(`/entries?week=${weekParam}`),
        api.get(`/timesheets?week=${weekParam}`).catch(() => ({ data: null })),
        api.get('/homeowners'),
      ]);

      // Organize entries by date
      const byDate = {};
      weekDates.forEach((d) => { byDate[d] = []; });
      (entriesRes.data.entries || entriesRes.data || []).forEach((e) => {
        const dk = e.date?.split('T')[0] || e.date;
        if (byDate[dk]) byDate[dk].push(e);
      });
      // Ensure at least one empty entry per day
      weekDates.forEach((d) => {
        if (byDate[d].length === 0) {
          byDate[d] = [{ id: `new-${d}-0`, date: d, homeownerId: '', hoursWorked: '', workDescription: '', _isNew: true }];
        }
      });

      setEntries(byDate);
      setTimesheet(timesheetRes.data?.timesheet || timesheetRes.data);
      setHomeowners(homeownersRes.data.homeowners || homeownersRes.data || []);
    } catch (err) {
      console.error('Failed to load week:', err);
    } finally {
      setLoading(false);
    }
  }, [weekParam]);

  useEffect(() => { loadWeek(); }, [loadWeek]);

  // Auto-save logic (debounced)
  // Only save when entry has all required fields
  function isEntryComplete(data) {
    return data.date && data.homeownerId && parseFloat(data.hoursWorked) > 0 && data.workDescription?.trim();
  }

  const saveEntry = useCallback(async (entryId, data) => {
    // Don't save incomplete entries
    if (!isEntryComplete(data)) {
      setSaveStatus('saved'); // Reset indicator, not an error
      return;
    }

    setSaveStatus('saving');
    // Normalize data for API
    const payload = {
      date: data.date,
      homeownerId: data.homeownerId,
      hoursWorked: parseFloat(data.hoursWorked),
      workDescription: data.workDescription?.trim() || '',
    };

    try {
      if (data._isNew || entryId.startsWith('new-')) {
        const res = await api.post('/entries', payload);
        // Replace temp ID with real ID
        setEntries((prev) => {
          const dk = data.date;
          return {
            ...prev,
            [dk]: prev[dk].map((e) => (e.id === entryId ? { ...res.data.entry || res.data, date: dk } : e)),
          };
        });
      } else {
        await api.put(`/entries/${entryId}`, payload);
      }
      setSaveStatus('saved');
    } catch (err) {
      console.error('Save failed:', err);
      setSaveStatus('error');
    }
  }, []);

  function handleEntryChange(entryId, updatedEntry) {
    const dk = updatedEntry.date;
    setEntries((prev) => ({
      ...prev,
      [dk]: prev[dk].map((e) => (e.id === entryId ? updatedEntry : e)),
    }));

    // Debounced save
    setSaveStatus('saving');
    pendingChanges.current[entryId] = updatedEntry;
    if (saveTimer.current) clearTimeout(saveTimer.current);
    saveTimer.current = setTimeout(() => {
      Object.entries(pendingChanges.current).forEach(([id, data]) => {
        saveEntry(id, data);
      });
      pendingChanges.current = {};
    }, 800);
  }

  function handleAddEntry(date) {
    const newEntry = {
      id: `new-${date}-${Date.now()}`,
      date,
      homeownerId: '',
      hoursWorked: '',
      workDescription: '',
      _isNew: true,
    };
    setEntries((prev) => ({ ...prev, [date]: [...(prev[date] || []), newEntry] }));
  }

  async function handleDeleteEntry(entryId) {
    try {
      if (!entryId.startsWith('new-')) {
        await api.delete(`/entries/${entryId}`);
      }
      setEntries((prev) => {
        const updated = {};
        Object.entries(prev).forEach(([dk, dayEntries]) => {
          const filtered = dayEntries.filter((e) => e.id !== entryId);
          updated[dk] = filtered.length > 0 ? filtered : [{ id: `new-${dk}-0`, date: dk, homeownerId: '', hoursWorked: '', workDescription: '', _isNew: true }];
        });
        return updated;
      });
      setSaveStatus('saved');
    } catch (err) {
      console.error('Delete failed:', err);
    }
  }

  // Fetch overtime for current week
  useEffect(() => {
    if (!weekParam) return;
    api.get(`/timesheets/overtime?week=${weekParam}`)
      .then((res) => setOvertime(res.data))
      .catch(() => setOvertime(null));
  }, [weekParam]);

  async function handleCopyPrevWeek() {
    const prevMonday = new Date(weekDates[0] + 'T00:00:00');
    prevMonday.setDate(prevMonday.getDate() - 7);
    const fromWeek = toLocalDateStr(prevMonday);
    
    if (!confirm(`Copy entries from week of ${fromWeek} to this week? This will replace any existing entries.`)) return;
    setCopying(true);
    try {
      const res = await api.post('/entries/copy-week', { fromWeek, toWeek: weekParam });
      alert(`Copied ${res.data.copied} entries!`);
      loadWeek();
    } catch (err) {
      alert(err.response?.data?.error || 'Failed to copy week');
    } finally {
      setCopying(false);
    }
  }

  async function handleSubmit() {
    setSubmitting(true);
    try {
      // Save any pending changes first
      if (saveTimer.current) clearTimeout(saveTimer.current);
      for (const [id, data] of Object.entries(pendingChanges.current)) {
        await saveEntry(id, data);
      }
      pendingChanges.current = {};

      const res = await api.post('/timesheets/submit', { weekStart: weekParam });
      setTimesheet(res.data);
    } catch (err) {
      alert(err.response?.data?.error || 'Failed to submit timesheet');
    } finally {
      setSubmitting(false);
    }
  }

  async function handleDownloadPdf() {
    if (!timesheetId) return;
    setPdfLoading(true);
    try {
      const res = await api.get(`/timesheets/${timesheetId}/pdf`, { responseType: 'blob' });
      const url = URL.createObjectURL(res.data);
      const a = document.createElement('a');
      a.href = url;
      a.download = `timesheet-${user.name}-${weekParam}.pdf`;
      a.click();
      URL.revokeObjectURL(url);
    } catch (err) {
      alert('Failed to generate PDF');
    } finally {
      setPdfLoading(false);
    }
  }

  const totalHours = Object.values(entries)
    .flat()
    .reduce((sum, e) => sum + (parseFloat(e.hoursWorked) || 0), 0);

  const today = toLocalDateStr(new Date());

  if (loading) {
    return (
      <div className="flex items-center justify-center py-20">
        <Loader2 size={32} className="animate-spin text-sky-500" />
      </div>
    );
  }

  return (
    <div className="space-y-4">
      {/* Week Navigator + Status */}
      <div className="bg-white dark:bg-gray-900 rounded-2xl border border-gray-200 dark:border-gray-800 p-4 space-y-3">
        <WeekNavigator selectedDate={selectedDate} onDateChange={setSelectedDate} />
        <div className="flex items-center justify-between">
          <div className="flex items-center gap-3">
            <StatusBadge status={timesheet?.status || 'draft'} />
            <SaveIndicator status={saveStatus} />
          </div>
          <div className="text-right">
            <div className="text-2xl font-bold text-gray-900 dark:text-white">{totalHours.toFixed(1)}</div>
            <div className="text-xs text-gray-500 dark:text-gray-400">hours this week</div>
          </div>
        </div>

        {/* Overtime indicator */}
        {overtime && overtime.overtimeHours > 0 && (
          <div className="flex items-center gap-2 px-3 py-2 rounded-xl bg-amber-50 dark:bg-amber-500/10 border border-amber-200 dark:border-amber-500/20">
            <TrendingUp size={16} className="text-amber-500" />
            <span className="text-sm font-medium text-amber-700 dark:text-amber-400">
              {overtime.overtimeHours.toFixed(1)}h overtime (over {overtime.threshold}h)
            </span>
          </div>
        )}

        {/* Copy previous week button */}
        {!isLocked && totalHours === 0 && (
          <button
            onClick={handleCopyPrevWeek}
            disabled={copying}
            className="w-full py-2.5 rounded-xl border-2 border-dashed border-sky-200 dark:border-sky-500/30 text-sky-600 dark:text-sky-400 text-sm font-medium flex items-center justify-center gap-2 hover:bg-sky-50 dark:hover:bg-sky-500/5 transition-all active:scale-[0.98]"
          >
            {copying ? <Loader2 size={16} className="animate-spin" /> : <Copy size={16} />}
            {copying ? 'Copying...' : 'Copy Previous Week'}
          </button>
        )}
      </div>

      {/* Day Cards */}
      <div className="space-y-3">
        {weekDates.map((date) => (
          <DayCard
            key={date}
            date={date}
            entries={entries[date] || []}
            homeowners={homeowners}
            onEntryChange={handleEntryChange}
            onAddEntry={handleAddEntry}
            onDeleteEntry={handleDeleteEntry}
            disabled={isLocked}
            defaultExpanded={date === today}
          />
        ))}
      </div>

      {/* Actions */}
      <div className="bg-white dark:bg-gray-900 rounded-2xl border border-gray-200 dark:border-gray-800 p-4 space-y-3">
        {!isLocked ? (
          <button
            onClick={handleSubmit}
            disabled={submitting || totalHours === 0}
            className="w-full py-4 rounded-2xl bg-gradient-to-r from-emerald-500 to-emerald-600 hover:from-emerald-600 hover:to-emerald-700 text-white font-semibold text-lg shadow-lg shadow-emerald-500/25 hover:shadow-emerald-500/40 transition-all disabled:opacity-50 disabled:cursor-not-allowed flex items-center justify-center gap-2 active:scale-[0.98]"
          >
            {submitting ? <Loader2 size={20} className="animate-spin" /> : <Send size={20} />}
            {submitting ? 'Submitting...' : 'Submit Timesheet'}
          </button>
        ) : (
          <div className="flex gap-2">
            <button
              onClick={handleDownloadPdf}
              disabled={pdfLoading}
              className="flex-1 py-3.5 rounded-xl bg-sky-50 dark:bg-sky-500/10 text-sky-600 dark:text-sky-400 font-semibold flex items-center justify-center gap-2 hover:bg-sky-100 dark:hover:bg-sky-500/20 transition-all"
            >
              {pdfLoading ? <Loader2 size={18} className="animate-spin" /> : <Download size={18} />}
              Download PDF
            </button>
            <button
              onClick={() => {
                if (timesheetId) {
                  window.open(`mailto:?subject=Timesheet - ${user.name} - Week of ${weekParam}&body=Please find my timesheet attached.`);
                }
              }}
              className="flex-1 py-3.5 rounded-xl bg-gray-50 dark:bg-gray-800 text-gray-600 dark:text-gray-400 font-semibold flex items-center justify-center gap-2 hover:bg-gray-100 dark:hover:bg-gray-700 transition-all"
            >
              <Mail size={18} />
              Email
            </button>
          </div>
        )}

        {timesheet?.status === 'rejected' && timesheet?.notes && (
          <div className="bg-red-50 dark:bg-red-500/10 border border-red-200 dark:border-red-500/20 rounded-xl px-4 py-3">
            <p className="text-sm font-medium text-red-600 dark:text-red-400">Rejected</p>
            <p className="text-sm text-red-500 dark:text-red-400/80 mt-1">{timesheet.notes}</p>
          </div>
        )}
      </div>
    </div>
  );
}