"use client";

import { useState, useTransition } from "react";
import {
  DndContext,
  closestCenter,
  PointerSensor,
  useSensor,
  useSensors,
  DragEndEvent,
} from "@dnd-kit/core";
import {
  SortableContext,
  verticalListSortingStrategy,
  useSortable,
  arrayMove,
} from "@dnd-kit/sortable";
import { CSS } from "@dnd-kit/utilities";
import Link from "next/link";
import { createModule, deleteModule, updateModule, reorderModules } from "@/lib/actions/course-actions";

interface Module {
  id: string;
  title: string;
  description: string | null;
  order: number;
  _count: { lessons: number };
}

function SortableModule({ mod, courseId }: { mod: Module; courseId: string }) {
  const [editing, setEditing] = useState(false);
  const [editValue, setEditValue] = useState(mod.title);
  const [editDesc, setEditDesc] = useState(mod.description ?? "");
  const [pending, startTransition] = useTransition();
  const { attributes, listeners, setNodeRef, transform, transition, isDragging } =
    useSortable({ id: mod.id });

  const style = {
    transform: CSS.Transform.toString(transform),
    transition,
    opacity: isDragging ? 0.4 : 1,
  };

  function handleUpdate(e: React.FormEvent<HTMLFormElement>) {
    e.preventDefault();
    const fd = new FormData(e.currentTarget);
    startTransition(() => updateModule(mod.id, courseId, fd));
    setEditing(false);
  }

  function handleDelete() {
    if (!confirm(`Удалить модуль "${mod.title}"? Все уроки будут удалены.`)) return;
    startTransition(() => deleteModule(mod.id, courseId));
  }

  return (
    <div
      ref={setNodeRef}
      style={{ ...style, border: "2px solid var(--border)", background: "var(--color-surface)" }}
      className="flex items-center gap-3 px-4 py-3"
    >
      <button
        type="button"
        {...attributes}
        {...listeners}
        className="cursor-grab active:cursor-grabbing text-lg select-none"
        style={{ color: "var(--muted-foreground)" }}
        aria-label="Перетащить"
      >
        ⠿
      </button>

      {editing ? (
        <form onSubmit={handleUpdate} className="flex flex-col gap-2 flex-1">
          <div className="flex items-center gap-2">
            <input
              name="title"
              value={editValue}
              onChange={(e) => setEditValue(e.target.value)}
              autoFocus
              required
              placeholder="Название модуля"
              className="flex-1 px-2 py-1 text-sm"
              style={{ border: "2px solid var(--foreground)", background: "var(--background)", outline: "none" }}
            />
            <button type="submit" disabled={pending} className="btn-aubade text-xs px-3 py-1 shrink-0">
              Сохранить
            </button>
            <button
              type="button"
              onClick={() => { setEditing(false); setEditValue(mod.title); setEditDesc(mod.description ?? ""); }}
              className="text-xs px-3 py-1 shrink-0"
              style={{ color: "var(--muted-foreground)" }}
            >
              Отмена
            </button>
          </div>
          <textarea
            name="description"
            value={editDesc}
            onChange={(e) => setEditDesc(e.target.value)}
            placeholder="Описание модуля (опционально)"
            rows={2}
            className="w-full px-2 py-1 text-sm resize-none"
            style={{ border: "1px solid var(--border)", background: "var(--background)", outline: "none" }}
          />
        </form>
      ) : (
        <>
          <div className="flex-1 min-w-0">
            <span className="font-medium text-sm">{mod.title}</span>
            {mod.description && (
              <p className="text-xs truncate mt-0.5" style={{ color: "var(--muted-foreground)" }}>
                {mod.description}
              </p>
            )}
          </div>
          <span className="text-xs" style={{ color: "var(--muted-foreground)" }}>
            {mod._count.lessons} {mod._count.lessons === 1 ? "урок" : mod._count.lessons < 5 ? "урока" : "уроков"}
          </span>
          <Link
            href={`/admin/courses/${courseId}/modules/${mod.id}`}
            className="btn-aubade text-xs px-3 py-1"
          >
            Уроки →
          </Link>
          <button
            type="button"
            onClick={() => setEditing(true)}
            className="text-xs"
            style={{ color: "var(--muted-foreground)" }}
          >
            Переименовать
          </button>
          <button
            type="button"
            onClick={handleDelete}
            disabled={pending}
            className="text-xs"
            style={{ color: "oklch(0.577 0.245 27.325)" }}
          >
            Удалить
          </button>
        </>
      )}
    </div>
  );
}

export function SortableModules({ courseId, modules }: { courseId: string; modules: Module[] }) {
  const [items, setItems] = useState(modules);
  const [creating, startTransition] = useTransition();

  const sensors = useSensors(useSensor(PointerSensor));

  function handleDragEnd(event: DragEndEvent) {
    const { active, over } = event;
    if (!over || active.id === over.id) return;

    const oldIndex = items.findIndex((m) => m.id === active.id);
    const newIndex = items.findIndex((m) => m.id === over.id);
    const newItems = arrayMove(items, oldIndex, newIndex);
    setItems(newItems);
    startTransition(() => reorderModules(courseId, newItems.map((m) => m.id)));
  }

  function handleCreate(e: React.FormEvent<HTMLFormElement>) {
    e.preventDefault();
    const fd = new FormData(e.currentTarget);
    e.currentTarget.reset();
    startTransition(() => createModule(courseId, fd));
  }

  return (
    <div className="space-y-2">
      <DndContext sensors={sensors} collisionDetection={closestCenter} onDragEnd={handleDragEnd}>
        <SortableContext items={items.map((m) => m.id)} strategy={verticalListSortingStrategy}>
          {items.map((mod) => (
            <SortableModule key={mod.id} mod={mod} courseId={courseId} />
          ))}
        </SortableContext>
      </DndContext>

      {items.length === 0 && (
        <p className="text-sm py-3" style={{ color: "var(--muted-foreground)" }}>
          Модулей пока нет. Добавьте первый.
        </p>
      )}

      <form onSubmit={handleCreate} className="flex gap-2 pt-3">
        <input
          name="title"
          placeholder="Название нового модуля"
          required
          disabled={creating}
          className="flex-1 max-w-xs px-3 py-2 text-sm"
          style={{ border: "2px solid var(--border)", background: "var(--background)", outline: "none" }}
          onFocus={(e) => (e.currentTarget.style.borderColor = "var(--foreground)")}
          onBlur={(e) => (e.currentTarget.style.borderColor = "var(--border)")}
        />
        <button type="submit" disabled={creating} className="btn-aubade text-xs px-4 py-2">
          {creating ? "Создание..." : "+ Модуль"}
        </button>
      </form>
    </div>
  );
}