import { useEffect, useState } from "react";
import { useNavigate, useParams } from "react-router-dom";
import { useForm, useWatch } from "react-hook-form";
import { z } from "zod";
import { zodResolver } from "@hookform/resolvers/zod";
import { ArrowLeft } from "lucide-react";

import { useLibrary } from "@/contexts/AdminLibraryContext";
import { useCourses } from "@/contexts/AdminCoursesContext";
import { useAuth } from "@/contexts/AuthContext";
import { PageMeta } from "@/contexts/MetadataContext";
import api from "@/utils/api.util";
import { Button } from "@/components/ui/button";
import { Input } from "@/components/ui/input";
import { Label } from "@/components/ui/label";
import { Textarea } from "@/components/ui/textarea";
import { Spinner } from "@/components/ui/spinner";
import {
  Select, SelectContent, SelectItem, SelectTrigger, SelectValue,
} from "@/components/ui/select";
import { useUnsavedChangesGuard } from "@/hooks/useUnsavedChangesGuard";
import CompletionRequirementBuilder from "@/modules/admin/components/courses/CompletionRequirementBuilder";
import ProductPricingCard from "@/modules/admin/components/products/ProductPricingCard";

const schema = z.object({
  title: z.string().min(1, "Title is required."),
  description: z.string().optional(),
  subscription: z.string().optional(),
});

function FieldError({ message }) {
  if (!message) return null;
  return <p className="text-xs text-destructive mt-1">{message}</p>;
}

export default function EditLibraryLesson() {
  const navigate = useNavigate();
  const { lessonId } = useParams();
  const { fetchLesson, updateLesson, lesson, loading, fetchLessonProduct, saveLessonProduct, removeLessonProduct } = useLibrary();
  const { fetchLessonRequirements, syncLessonRequirements } = useCourses();
  const { user } = useAuth();

  const [tierCategories, setTierCategories] = useState([]);
  useEffect(() => {
    api.get("/admin/tiers/categories")
      .then(({ data }) => setTierCategories((data.data ?? []).filter((c) => c.is_active)))
      .catch(() => {});
  }, []);

  const { register, handleSubmit, reset, control, setValue, formState: { errors, isDirty } } = useForm({
    resolver: zodResolver(schema),
    defaultValues: { title: "", description: "", subscription: "free" },
  });

  const { bypassOnce, dialog: unsavedChangesDialog } = useUnsavedChangesGuard(isDirty);

  const watchedSubscr = useWatch({ control, name: "subscription" });
  const defaultTierSlug = tierCategories.find((c) => c.is_default)?.slug || "free";

  useEffect(() => {
    fetchLesson(lessonId);
  }, [lessonId]);

  useEffect(() => {
    if (lesson && String(lesson.lesson_id) === String(lessonId)) {
      reset({ title: lesson.title ?? "", description: lesson.description ?? "", subscription: lesson.subscription || defaultTierSlug });
    }
  }, [lesson, lessonId, reset]);

  const onSubmit = async (data) => {
    const result = await updateLesson(lessonId, { ...data, subscription: data.subscription || defaultTierSlug, updatedBy: user?.user_id });
    if (!result) return;
    bypassOnce();
    navigate(`/admin/lessons/${lessonId}/view`);
  };

  return (
    <section className="bg-muted h-full">
      <PageMeta title={lesson ? `Edit Lesson – ${lesson.title} - STARR` : undefined} />
      <div className="lg:container lg:mx-auto lg:px-0 flex flex-col items-center px-4 py-10">

        <div className="w-full max-w-2xl mx-auto">
          <div className="flex items-center gap-3 mb-6">
            <Button type="button" variant="ghost" size="icon" onClick={() => navigate(`/admin/lessons/${lessonId}/view`)}>
              <ArrowLeft className="h-4 w-4" />
            </Button>
            <div>
              <h1 className="text-xl font-semibold">Edit Lesson</h1>
              <p className="text-sm text-muted-foreground">
                Changes apply everywhere this lesson is attached.
              </p>
            </div>
          </div>

          <form onSubmit={handleSubmit(onSubmit)} className="space-y-6">
            <div className="rounded-lg border bg-card p-6 space-y-5">

              <div className="space-y-1.5">
                <Label htmlFor="title">Title <span className="text-destructive">*</span></Label>
                <Input id="title" placeholder="Lesson title" {...register("title")} />
                <FieldError message={errors.title?.message} />
              </div>

              <div className="space-y-1.5">
                <Label htmlFor="description">Description</Label>
                <Textarea id="description" placeholder="Optional description" rows={3} {...register("description")} />
              </div>

              <div className="space-y-1.5">
                <Label>Subscription</Label>
                <Select
                  value={watchedSubscr || defaultTierSlug}
                  onValueChange={(val) => setValue("subscription", val, { shouldDirty: true })}
                >
                  <SelectTrigger>
                    <SelectValue placeholder="No tier gate" />
                  </SelectTrigger>
                  <SelectContent>
                    {tierCategories.map((c) => (
                      <SelectItem key={c.slug} value={c.slug}>
                        {c.name}
                      </SelectItem>
                    ))}
                  </SelectContent>
                </Select>
                <p className="text-xs text-muted-foreground">
                  Optional. Gates this lesson directly, independent of any unit it may later be attached to.
                </p>
              </div>

            </div>

            <div className="flex justify-end gap-3">
              <Button type="button" variant="outline" onClick={() => navigate(`/admin/lessons/${lessonId}/view`)} disabled={loading}>
                Cancel
              </Button>
              <Button type="submit" disabled={loading}>
                {loading && <Spinner className="h-4 w-4 mr-2" />}
                Save Changes
              </Button>
            </div>
          </form>

          <div className="rounded-lg border bg-card p-6 space-y-4 mt-6">
            <div>
              <h2 className="text-sm font-semibold">Completion Requirements</h2>
              <p className="text-xs text-muted-foreground">What a learner must do for this lesson to count as complete, wherever it's attached.</p>
            </div>
            <CompletionRequirementBuilder
              entityType="lesson"
              fetchFn={fetchLessonRequirements}
              syncFn={syncLessonRequirements}
              args={[null, null, lessonId]}
            />
          </div>

          <div className="rounded-lg border bg-card p-6 space-y-4 mt-6">
            <div>
              <h2 className="text-sm font-semibold">Pricing</h2>
              <p className="text-xs text-muted-foreground">Optional individual-purchase listing for this lesson.</p>
            </div>
            <ProductPricingCard
              label="this lesson"
              fetchFn={fetchLessonProduct}
              saveFn={saveLessonProduct}
              removeFn={removeLessonProduct}
              args={[lessonId]}
            />
          </div>
        </div>
      </div>

      {unsavedChangesDialog}
    </section>
  );
}