import { useEffect, useState } from "react";
import { useNavigate, useParams, Link } from "react-router-dom";
import {
  ArrowLeft, House, Plus, Link2, Unlink, Pencil,
  ChevronUp, ChevronDown, Clock, ClipboardList, PlusCircle,
  LayoutTemplate, BookOpen,
} from "lucide-react";

import { useLibrary } from "@/contexts/AdminLibraryContext";
import { PageMeta } from "@/contexts/MetadataContext";
import AppBreadcrumb from "@/components/generic/Breadcrumb/AppBreadcrumb";
import AttachLessonsDialog from "../../../components/library/AttachLessonsDialog";
import AttachCoursesDialog from "../../../components/library/AttachCoursesDialog";
import { Button } from "@/components/ui/button";
import { Badge } from "@/components/ui/badge";
import { Spinner } from "@/components/ui/spinner";
import { formatDuration } from "@/utils/timestamp.util";

export default function ViewLibraryUnit() {
  const navigate = useNavigate();
  const { unitId } = useParams();
  const {
    fetchUnit, unit, loading,
    attachLessonsToUnit, detachLessonFromUnit, detachUnitFromCourse, attachUnitToCourses, reorderUnitLessons,
  } = useLibrary();

  const [initializing, setInitializing] = useState(true);
  const [attachOpen, setAttachOpen] = useState(false);
  const [attachCourseOpen, setAttachCourseOpen] = useState(false);
  const [descExpanded, setDescExpanded] = useState(false);

  useEffect(() => {
    (async () => {
      await fetchUnit(unitId);
      setInitializing(false);
    })();
  }, [unitId]);

  const items = [
    { label: "Home", icon: <House className="size-4" />, to: "/admin" },
    { label: "Units", to: "/admin/units" },
    { label: unit?.title ?? "..." },
  ];

  const lessons = unit?.lessons ?? [];
  const courses = unit?.courses ?? [];

  const moveLesson = async (index, direction) => {
    const target = index + direction;
    if (target < 0 || target >= lessons.length) return;
    const reordered = [...lessons];
    [reordered[index], reordered[target]] = [reordered[target], reordered[index]];
    await reorderUnitLessons(unitId, reordered.map((l) => l.lesson_id));
    fetchUnit(unitId);
  };

  const handleDetach = async (lessonId) => {
    await detachLessonFromUnit(unitId, lessonId);
    fetchUnit(unitId);
  };

  const handleDetachCourse = async (courseId) => {
    await detachUnitFromCourse(unitId, courseId);
    fetchUnit(unitId);
  };

  const handleAttachCourses = async (courseIds) => {
    await attachUnitToCourses(unitId, courseIds);
    fetchUnit(unitId);
  };

  const handleAttach = async (lessonIds) => {
    await attachLessonsToUnit(unitId, lessonIds);
    fetchUnit(unitId);
  };

  if (initializing) {
    return (
      <div className="flex items-center justify-center h-64">
        <Spinner className="h-6 w-6" />
      </div>
    );
  }

  return (
    <section className="bg-muted h-full">
      <PageMeta title={unit ? `${unit.title} - Units - STARR` : undefined} />
      <div className="lg:container lg:mx-auto lg:px-0 flex flex-col items-start px-4">
        <div className="flex flex-col gap-2 my-6">
          <AppBreadcrumb items={items} />
        </div>

        <div className="w-full space-y-6 pb-10">

          {/* ── Unit header ── */}
          <div className="bg-card rounded-xl border p-6 space-y-4">
            <div className="flex items-start justify-between gap-4">
              <div className="max-w-2xl">
                <h1 className="text-xl font-semibold">{unit?.title}</h1>
                {unit?.description && (
                  <div className="mt-0.5">
                    <p className={`text-sm text-muted-foreground ${descExpanded ? '' : 'line-clamp-2'}`}>
                      {unit.description}
                    </p>
                    <button
                      type="button"
                      onClick={() => setDescExpanded((v) => !v)}
                      className="text-xs font-medium text-primary hover:underline mt-0.5"
                    >
                      {descExpanded ? 'See less' : 'See more'}
                    </button>
                  </div>
                )}
              </div>
              <div className="flex gap-2 shrink-0">
                <Button size="sm" variant="outline" onClick={() => setAttachCourseOpen(true)}>
                  <Link2 className="h-3.5 w-3.5 mr-1.5" /> Attach to Course
                </Button>
                {courses.map((c) => (
                  <Button
                    key={c.course_id}
                    size="sm"
                    variant="destructive"
                    onClick={() => handleDetachCourse(c.course_id)}
                    disabled={loading}
                    title={`Detach from ${c.title} (unit stays in library)`}
                  >
                    <Unlink className="h-3.5 w-3.5 mr-1.5" /> Detach from Course
                  </Button>
                ))}
                <Button size="sm" variant="outline" onClick={() => navigate(`/admin/units/${unitId}/edit`)}>
                  <Pencil className="h-3.5 w-3.5 mr-1.5" /> Edit
                </Button>
                {unit?.quiz ? (
                  <Button size="sm" variant="outline" onClick={() => navigate(`/admin/units/${unitId}/quiz/view`)}>
                    <ClipboardList className="h-3.5 w-3.5 mr-1.5" /> View Quiz
                  </Button>
                ) : (
                  <Button size="sm" variant="outline" onClick={() => navigate(`/admin/units/${unitId}/quiz/edit`)}>
                    <PlusCircle className="h-3.5 w-3.5 mr-1.5" /> Create Quiz
                  </Button>
                )}
              </div>
            </div>

            {/* Stats row */}
            <div className="grid grid-cols-2 lg:grid-cols-5 gap-3">
              <div className="bg-muted/60 rounded-lg p-3 space-y-1">
                <p className="text-xs text-muted-foreground uppercase tracking-wide font-medium">Lessons</p>
                <p className="font-semibold text-sm">{lessons.length}</p>
              </div>
              <div className="bg-muted/60 rounded-lg p-3 space-y-1">
                <p className="text-xs text-muted-foreground uppercase tracking-wide font-medium">Duration</p>
                <p className="font-semibold text-sm">{formatDuration(unit?.duration_seconds ?? 0)}</p>
              </div>
              <div className="bg-muted/60 rounded-lg p-3 space-y-1">
                <p className="text-xs text-muted-foreground uppercase tracking-wide font-medium">Quiz</p>
                <p className="font-semibold text-sm">{unit?.quiz ? unit.quiz.title || "Unit Quiz" : "None"}</p>
              </div>
              <div className="bg-muted/60 rounded-lg p-3 space-y-1">
                <p className="text-xs text-muted-foreground uppercase tracking-wide font-medium">Used In</p>
                <p className="font-semibold text-sm">
                  {courses.length > 0 ? `${courses.length} course${courses.length === 1 ? "" : "s"}` : "Standalone"}
                </p>
              </div>
              <div className="bg-muted/60 rounded-lg p-3 space-y-1">
                <p className="text-xs text-muted-foreground uppercase tracking-wide font-medium">Subscription</p>
                <Badge variant={unit?.subscription ? "outline" : "secondary"} className="capitalize">
                  {unit?.subscription ?? "No subscription gate"}
                </Badge>
              </div>
            </div>

            {/* Attached courses */}
            {courses.length > 0 && (
              <div className="flex flex-wrap items-center gap-2 pt-1">
                <span className="text-xs text-muted-foreground uppercase tracking-wide font-medium">Courses:</span>
                {courses.map((c) => (
                  <Link key={c.course_id} to={`/admin/courses/${c.course_id}/view`}>
                    <Badge variant="secondary" className="hover:bg-muted cursor-pointer">
                      <BookOpen className="h-3 w-3 mr-1" /> {c.title}
                    </Badge>
                  </Link>
                ))}
              </div>
            )}
          </div>

          {/* ── Lessons manager ── */}
          <div className="bg-card rounded-xl border">
            <div className="flex items-center justify-between p-4 border-b">
              <div>
                <h2 className="font-semibold">Lessons</h2>
                <p className="text-xs text-muted-foreground">
                  It can be standalone too attach existing ones or create new.
                </p>
              </div>
              <div className="flex gap-2">
                <Button size="sm" variant="outline" onClick={() => setAttachOpen(true)}>
                  <Link2 className="h-3.5 w-3.5 mr-1.5" /> Select
                </Button>
                <Button size="sm" onClick={() => navigate(`/admin/lessons/add?unit_id=${unitId}`)}>
                  <Plus className="h-3.5 w-3.5 mr-1.5" /> Create
                </Button>
              </div>
            </div>

            {lessons.length === 0 ? (
              <p className="text-sm text-muted-foreground text-center py-10">
                No lessons attached yet — attach one from the library or create a new one.
              </p>
            ) : (
              <div className="divide-y">
                {lessons.map((l, i) => (
                  <div key={l.lesson_id} className="flex items-center gap-3 px-4 py-3">
                    <span className="text-xs font-mono text-muted-foreground w-6 text-right shrink-0">
                      {i + 1}.
                    </span>
                    <div className="flex flex-col gap-0.5 shrink-0">
                      <button
                        type="button"
                        className="text-muted-foreground hover:text-foreground disabled:opacity-30"
                        disabled={i === 0 || loading}
                        onClick={() => moveLesson(i, -1)}
                        aria-label="Move up"
                      >
                        <ChevronUp className="h-3.5 w-3.5" />
                      </button>
                      <button
                        type="button"
                        className="text-muted-foreground hover:text-foreground disabled:opacity-30"
                        disabled={i === lessons.length - 1 || loading}
                        onClick={() => moveLesson(i, 1)}
                        aria-label="Move down"
                      >
                        <ChevronDown className="h-3.5 w-3.5" />
                      </button>
                    </div>
                    <div className="flex-1 min-w-0">
                      <p className="text-sm font-medium truncate">{l.title}</p>
                      {l.description && (
                        <p className="text-xs w-64 text-muted-foreground truncate">{l.description}</p>
                      )}
                    </div>
                    <Badge variant="secondary" className="text-xs shrink-0 tabular-nums">
                      <Clock className="h-3 w-3 mr-1" /> {formatDuration(l.duration_seconds ?? 0)}
                    </Badge>
                    <Button
                      size="sm" variant="outline"
                      onClick={() => navigate(`/admin/lessons/${l.lesson_id}/page`)}
                     
                    >
                      <LayoutTemplate /> Page Builder
                    </Button>
                    <Button
                      size="sm" 
                      variant="destructive"
                      onClick={() => handleDetach(l.lesson_id)}
                      disabled={loading}
                      title="Detach from unit (lesson stays in library)"
                    >
                      <Unlink className="h-3.5 w-3.5" /> Detach
                    </Button>
                  </div>
                ))}
              </div>
            )}
          </div>
        </div>
      </div>

      <AttachLessonsDialog
        open={attachOpen}
        onOpenChange={setAttachOpen}
        attachedLessonIds={lessons.map((l) => l.lesson_id)}
        onAttach={handleAttach}
        loading={loading}
      />

      <AttachCoursesDialog
        open={attachCourseOpen}
        onOpenChange={setAttachCourseOpen}
        attachedCourseIds={courses.map((c) => c.course_id)}
        onAttach={handleAttachCourses}
        loading={loading}
      />
    </section>
  );
}