import { useState, useMemo, useEffect } from 'react';
import { useMediaQuery, DESKTOP } from '@/hooks/useMediaQuery';
import { useLocation } from 'react-router-dom';
import { Plus, CheckSquare, CheckCircle2, AlertCircle } from 'lucide-react';
import { useQuery } from '@tanstack/react-query';
import api from '@/lib/api';
import type { Todo } from '@/types';
import { isTodoOverdue } from '@/lib/utils';
import { Button } from '@/components/ui/button';
import { Select } from '@/components/ui/select';
import { Card, CardContent } from '@/components/ui/card';
import { ListSkeleton } from '@/components/ui/skeleton';
import { CategoryFilterBar } from '@/components/shared';
import MobileDetailOverlay from '@/components/shared/MobileDetailOverlay';
import { useCategoryOrder } from '@/hooks/useCategoryOrder';
import TodoList from './TodoList';
import TodoDetailPanel from './TodoDetailPanel';

const priorityFilters = [
  { value: '', label: 'All' },
  { value: 'none', label: 'None' },
  { value: 'low', label: 'Low' },
  { value: 'medium', label: 'Medium' },
  { value: 'high', label: 'High' },
] as const;

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

  const isDesktop = useMediaQuery(DESKTOP);

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

  // Filters
  const [priorityFilter, setPriorityFilter] = useState('');
  const [activeFilters, setActiveFilters] = useState<string[]>([]);
  const [showCompleted, setShowCompleted] = useState(true);
  const [search, setSearch] = useState('');

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

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

  const allCategories = useMemo(() => {
    const cats = new Set<string>();
    todos.forEach((t) => {
      if (t.category) cats.add(t.category);
    });
    return Array.from(cats).sort();
  }, [todos]);

  const { orderedCategories, reorder: reorderCategories } = useCategoryOrder('todos', allCategories);

  const filteredTodos = useMemo(
    () =>
      todos.filter((todo) => {
        if (priorityFilter && todo.priority !== priorityFilter) return false;
        if (activeFilters.length > 0) {
          if (!todo.category || !activeFilters.includes(todo.category)) return false;
        }
        if (!showCompleted && todo.completed) return false;
        if (search && !todo.title.toLowerCase().includes(search.toLowerCase()))
          return false;
        return true;
      }),
    [todos, priorityFilter, activeFilters, showCompleted, search]
  );

  const totalCount = filteredTodos.filter((t) => !t.completed).length;
  const completedCount = filteredTodos.filter((t) => t.completed).length;
  const overdueCount = filteredTodos.filter((t) => isTodoOverdue(t.due_date, t.completed)).length;

  const panelOpen = panelMode !== 'closed';
  const selectedTodo = useMemo(
    () => todos.find((t) => t.id === selectedTodoId) ?? null,
    [selectedTodoId, todos],
  );

  const handleSelect = (todo: Todo) => {
    setSelectedTodoId(todo.id);
    setPanelMode('view');
  };

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

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

  // CategoryFilterBar handlers
  const toggleAll = () => setActiveFilters([]);
  const toggleCompleted = () => setShowCompleted((p) => !p);
  const toggleCategory = (cat: string) => {
    setActiveFilters((prev) =>
      prev.includes(cat) ? prev.filter((c) => c !== cat) : [...prev, cat]
    );
  };
  const selectAllCategories = () => {
    const allSelected = orderedCategories.every((c) => activeFilters.includes(c));
    setActiveFilters(allSelected ? [] : [...orderedCategories]);
  };

  // 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-4 md:px-6 min-h-[4rem] flex items-center gap-2 md:gap-4 flex-wrap py-2 md:py-0 md:h-16 md:flex-nowrap shrink-0">
        <h1 className="font-heading text-xl md:text-2xl font-bold tracking-tight">Todos</h1>

        {/* Priority filter */}
        <Select
          value={priorityFilter}
          onChange={(e) => setPriorityFilter(e.target.value as typeof priorityFilter)}
          className="h-8 text-sm w-auto pr-8 md:hidden"
        >
          {priorityFilters.map((pf) => (
            <option key={pf.value} value={pf.value}>{pf.label}</option>
          ))}
        </Select>
        <div className="hidden md:flex items-center rounded-md border border-border overflow-hidden ml-4">
          {priorityFilters.map((pf) => (
            <button
              key={pf.value}
              onClick={() => setPriorityFilter(pf.value)}
              className={`px-3 py-1.5 text-sm font-medium transition-colors duration-150 ${
                priorityFilter === pf.value
                  ? 'bg-accent/15 text-accent'
                  : 'text-muted-foreground hover:text-foreground hover:bg-card-elevated'
              }`}
              style={{
                backgroundColor:
                  priorityFilter === pf.value ? 'hsl(var(--accent-color) / 0.15)' : undefined,
                color: priorityFilter === pf.value ? 'hsl(var(--accent-color))' : undefined,
              }}
            >
              {pf.label}
            </button>
          ))}
        </div>

        {/* Category filter bar (All + Completed + Categories with drag) */}
        <div className="w-full md:flex-1 md:w-auto min-w-0 order-last md:order-none">
          <CategoryFilterBar
            activeFilters={activeFilters}
            pinnedLabel="Completed"
            showPinned={showCompleted}
            categories={orderedCategories}
            onToggleAll={toggleAll}
            onTogglePinned={toggleCompleted}
            onToggleCategory={toggleCategory}
            onSelectAllCategories={selectAllCategories}
            onReorderCategories={reorderCategories}
            searchValue={search}
            onSearchChange={setSearch}
          />
        </div>

        <Button onClick={handleCreateNew} size="sm">
          <Plus className="h-4 w-4 md:mr-2" /><span className="hidden md:inline">Add Todo</span>
        </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-4 md:px-6 py-5">
            {/* Summary stats */}
            {!isLoading && todos.length > 0 && (
              <div className="grid gap-1.5 md:gap-2.5 grid-cols-3 mb-5">
                <Card className="bg-gradient-to-br from-accent/[0.03] to-transparent">
                  <CardContent className="p-2.5 md:p-4 flex items-center gap-2 md:gap-3">
                    <div className="p-1.5 rounded-md bg-blue-500/10 hidden sm:block">
                      <CheckSquare className="h-4 w-4 text-blue-400" />
                    </div>
                    <div>
                      <p className="text-[9px] md:text-[10px] tracking-wider uppercase text-muted-foreground">
                        Open
                      </p>
                      <p className="font-heading text-lg md:text-xl font-bold tabular-nums">{totalCount}</p>
                    </div>
                  </CardContent>
                </Card>
                <Card className="bg-gradient-to-br from-accent/[0.03] to-transparent">
                  <CardContent className="p-2.5 md:p-4 flex items-center gap-2 md:gap-3">
                    <div className="p-1.5 rounded-md bg-green-500/10 hidden sm:block">
                      <CheckCircle2 className="h-4 w-4 text-green-400" />
                    </div>
                    <div>
                      <p className="text-[9px] md:text-[10px] tracking-wider uppercase text-muted-foreground">
                        Completed
                      </p>
                      <p className="font-heading text-lg md:text-xl font-bold tabular-nums">{completedCount}</p>
                    </div>
                  </CardContent>
                </Card>
                <Card className="bg-gradient-to-br from-accent/[0.03] to-transparent">
                  <CardContent className="p-2.5 md:p-4 flex items-center gap-2 md:gap-3">
                    <div className="p-1.5 rounded-md bg-red-500/10 hidden sm:block">
                      <AlertCircle className="h-4 w-4 text-red-400" />
                    </div>
                    <div>
                      <p className="text-[9px] md:text-[10px] tracking-wider uppercase text-muted-foreground">
                        Overdue
                      </p>
                      <p className="font-heading text-lg md:text-xl font-bold tabular-nums">{overdueCount}</p>
                    </div>
                  </CardContent>
                </Card>
              </div>
            )}

            {isLoading ? (
              <ListSkeleton rows={6} />
            ) : (
              <TodoList
                todos={filteredTodos}
                onEdit={handleSelect}
                onAdd={handleCreateNew}
              />
            )}
          </div>
        </div>

        {/* Detail panel (desktop) */}
        {panelOpen && isDesktop && (
          <div
            className="overflow-hidden transition-all duration-300 ease-[cubic-bezier(0.16,1,0.3,1)] w-[45%]"
          >
            <TodoDetailPanel
              todo={panelMode === 'view' ? selectedTodo : null}
              isCreating={panelMode === 'create'}
              onClose={handlePanelClose}
              onSaved={panelMode === 'create' ? handlePanelClose : undefined}
            />
          </div>
        )}
      </div>

      {/* Mobile detail panel overlay */}
      {panelOpen && !isDesktop && (
        <MobileDetailOverlay open={true} onClose={handlePanelClose}>
          <TodoDetailPanel
            todo={panelMode === 'view' ? selectedTodo : null}
            isCreating={panelMode === 'create'}
            onClose={handlePanelClose}
            onSaved={panelMode === 'create' ? handlePanelClose : undefined}
          />
        </MobileDetailOverlay>
      )}
    </div>
  );
}