import { useState, useMemo, useEffect } from 'react';
import { useLocation } from 'react-router-dom';
import { Plus, Bell, BellOff, AlertCircle, Search } from 'lucide-react';
import { useQuery } from '@tanstack/react-query';
import { isPast, isToday, parseISO } from 'date-fns';
import api from '@/lib/api';
import type { Reminder } from '@/types';
import { Button } from '@/components/ui/button';
import { Input } from '@/components/ui/input';
import { Card, CardContent } from '@/components/ui/card';
import { ListSkeleton } from '@/components/ui/skeleton';
import ReminderList from './ReminderList';
import ReminderDetailPanel from './ReminderDetailPanel';

const statusFilters = [
  { value: 'active', label: 'Active' },
  { value: 'dismissed', label: 'Dismissed' },
  { value: 'all', label: 'All' },
] as const;

type StatusFilter = (typeof statusFilters)[number]['value'];

export default function RemindersPage() {
  const location = useLocation();

  // Panel state
  const [selectedReminderId, setSelectedReminderId] = useState<number | null>(null);
  const [panelMode, setPanelMode] = useState<'closed' | 'view' | 'create'>('closed');

  const [filter, setFilter] = useState<StatusFilter>('active');
  const [search, setSearch] = useState('');

  // Handle navigation state from dashboard
  useEffect(() => {
    const state = location.state as { reminderId?: number } | null;
    if (state?.reminderId) {
      setSelectedReminderId(state.reminderId);
      setPanelMode('view');
      window.history.replaceState({}, '');
    }
  }, [location.state]);

  const { data: reminders = [], isLoading } = useQuery({
    queryKey: ['reminders'],
    queryFn: async () => {
      const { data } = await api.get<Reminder[]>('/reminders');
      return data;
    },
  });

  const filteredReminders = useMemo(
    () =>
      reminders.filter((r) => {
        if (filter === 'active' && r.is_dismissed) return false;
        if (filter === 'dismissed' && !r.is_dismissed) return false;
        if (search && !r.title.toLowerCase().includes(search.toLowerCase())) return false;
        return true;
      }),
    [reminders, filter, search]
  );

  const activeCount = reminders.filter((r) => !r.is_dismissed).length;
  const overdueCount = reminders.filter(
    (r) => !r.is_dismissed && r.remind_at && isPast(parseISO(r.remind_at)) && !isToday(parseISO(r.remind_at))
  ).length;
  const dismissedCount = reminders.filter((r) => r.is_dismissed).length;

  const panelOpen = panelMode !== 'closed';
  const selectedReminder = useMemo(
    () => reminders.find((r) => r.id === selectedReminderId) ?? null,
    [selectedReminderId, reminders],
  );

  const handleSelect = (reminder: Reminder) => {
    setSelectedReminderId(reminder.id);
    setPanelMode('view');
  };

  const handleCreateNew = () => {
    setSelectedReminderId(null);
    setPanelMode('create');
  };

  const handlePanelClose = () => {
    setPanelMode('closed');
    setSelectedReminderId(null);
  };

  // Escape key closes panel
  useEffect(() => {
    if (!panelOpen) return;
    const handler = (e: KeyboardEvent) => {
      if (e.key === 'Escape') handlePanelClose();
    };
    document.addEventListener('keydown', handler);
    return () => document.removeEventListener('keydown', handler);
  }, [panelOpen]);

  return (
    <div className="flex flex-col h-full animate-fade-in">
      {/* Header */}
      <div className="border-b bg-card px-6 h-16 flex items-center gap-4 shrink-0">
        <h1 className="font-heading text-2xl font-bold tracking-tight">Reminders</h1>

        <div className="flex items-center rounded-md border border-border overflow-hidden ml-4">
          {statusFilters.map((sf) => (
            <button
              key={sf.value}
              onClick={() => setFilter(sf.value)}
              className={`px-3 py-1.5 text-sm font-medium transition-colors duration-150 ${
                filter === sf.value
                  ? 'bg-accent/15 text-accent'
                  : 'text-muted-foreground hover:text-foreground hover:bg-card-elevated'
              }`}
              style={{
                backgroundColor:
                  filter === sf.value ? 'hsl(var(--accent-color) / 0.15)' : undefined,
                color: filter === sf.value ? 'hsl(var(--accent-color))' : undefined,
              }}
            >
              {sf.label}
            </button>
          ))}
        </div>

        <div className="flex-1" />

        <div className="relative">
          <Search className="absolute left-2.5 top-1/2 -translate-y-1/2 h-3.5 w-3.5 text-muted-foreground" />
          <Input
            placeholder="Search..."
            value={search}
            onChange={(e) => setSearch(e.target.value)}
            className="w-52 h-8 pl-8 text-sm ring-inset"
          />
        </div>

        <Button onClick={handleCreateNew} size="sm">
          <Plus className="mr-2 h-4 w-4" />
          Add Reminder
        </Button>
      </div>

      {/* Main content — list + detail panel */}
      <div className="flex-1 overflow-hidden flex">
        <div
          className={`overflow-y-auto transition-all duration-300 ease-[cubic-bezier(0.16,1,0.3,1)] ${
            panelOpen ? 'w-full lg:w-[55%]' : 'w-full'
          }`}
        >
          <div className="px-6 py-5">
            {/* Summary stats */}
            {!isLoading && reminders.length > 0 && (
              <div className="grid gap-2.5 grid-cols-3 mb-5">
                <Card className="bg-gradient-to-br from-accent/[0.03] to-transparent">
                  <CardContent className="p-4 flex items-center gap-3">
                    <div className="p-1.5 rounded-md bg-orange-500/10">
                      <Bell className="h-4 w-4 text-orange-400" />
                    </div>
                    <div>
                      <p className="text-[10px] tracking-wider uppercase text-muted-foreground">
                        Active
                      </p>
                      <p className="font-heading text-xl font-bold tabular-nums">{activeCount}</p>
                    </div>
                  </CardContent>
                </Card>
                <Card className="bg-gradient-to-br from-accent/[0.03] to-transparent">
                  <CardContent className="p-4 flex items-center gap-3">
                    <div className="p-1.5 rounded-md bg-red-500/10">
                      <AlertCircle className="h-4 w-4 text-red-400" />
                    </div>
                    <div>
                      <p className="text-[10px] tracking-wider uppercase text-muted-foreground">
                        Overdue
                      </p>
                      <p className="font-heading text-xl font-bold tabular-nums">{overdueCount}</p>
                    </div>
                  </CardContent>
                </Card>
                <Card className="bg-gradient-to-br from-accent/[0.03] to-transparent">
                  <CardContent className="p-4 flex items-center gap-3">
                    <div className="p-1.5 rounded-md bg-gray-500/10">
                      <BellOff className="h-4 w-4 text-gray-400" />
                    </div>
                    <div>
                      <p className="text-[10px] tracking-wider uppercase text-muted-foreground">
                        Dismissed
                      </p>
                      <p className="font-heading text-xl font-bold tabular-nums">{dismissedCount}</p>
                    </div>
                  </CardContent>
                </Card>
              </div>
            )}

            {isLoading ? (
              <ListSkeleton rows={6} />
            ) : (
              <ReminderList
                reminders={filteredReminders}
                onEdit={handleSelect}
                onAdd={handleCreateNew}
              />
            )}
          </div>
        </div>

        {/* Detail panel (desktop) */}
        <div
          className={`overflow-hidden transition-all duration-300 ease-[cubic-bezier(0.16,1,0.3,1)] ${
            panelOpen ? 'hidden lg:block lg:w-[45%]' : 'w-0 opacity-0'
          }`}
        >
          <ReminderDetailPanel
            reminder={panelMode === 'view' ? selectedReminder : null}
            isCreating={panelMode === 'create'}
            onClose={handlePanelClose}
            onSaved={panelMode === 'create' ? handlePanelClose : undefined}
          />
        </div>
      </div>

      {/* Mobile detail panel overlay */}
      {panelOpen && (
        <div
          className="lg:hidden fixed inset-0 z-50 bg-background/80 backdrop-blur-sm"
          onClick={handlePanelClose}
        >
          <div
            className="fixed inset-y-0 right-0 w-full sm:w-[400px] bg-card border-l border-border shadow-lg"
            onClick={(e) => e.stopPropagation()}
          >
            <ReminderDetailPanel
              reminder={panelMode === 'view' ? selectedReminder : null}
              isCreating={panelMode === 'create'}
              onClose={handlePanelClose}
              onSaved={panelMode === 'create' ? handlePanelClose : undefined}
            />
          </div>
        </div>
      )}
    </div>
  );
}