import { useEffect } from "react";
import { useNavigate, useParams } from "react-router-dom";
import { useForm, useFieldArray } from "react-hook-form";
import { z } from "zod";
import { zodResolver } from "@hookform/resolvers/zod";
import { ArrowLeft, Plus, Trash2 } from "lucide-react";

import { useCourses } from "@/contexts/AdminCoursesContext";
import { useAuth } from "@/contexts/AuthContext";
import { PageMeta } from "@/contexts/MetadataContext";
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";

const schema = z.object({
  title: z.string().min(1, "Title is required."),
  description: z.string().optional(),
  order: z.coerce.number().min(0).default(0),
  objectives: z.array(
    z.object({ value: z.string().min(1, "Objective cannot be empty.") })
  ).optional(),
});

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

export default function AddLesson() {
  const navigate = useNavigate();
  const { courseId, unitId } = useParams();
  const { createLesson, fetchUnit, course, unit, loading } = useCourses();
  const { user } = useAuth();

  const { register, handleSubmit, control, formState: { errors } } = useForm({
    resolver: zodResolver(schema),
    defaultValues: { title: "", description: "", order: 0, objectives: [] },
  });

  const { fields, append, remove } = useFieldArray({ control, name: "objectives" });

  useEffect(() => {
    fetchUnit(courseId, unitId);
  }, [courseId, unitId]);

  const onSubmit = async (data) => {
    const payload = {
      ...data,
      objectives: data.objectives?.map((o) => o.value) ?? [],
      createdBy: user?.user_id,
    };
    const result = await createLesson(courseId, unitId, payload);
    if (!result) return;
    navigate(`/admin/courses/${courseId}/units/${unitId}/lessons`);
  };

  return (
    <section className="bg-muted h-full">
      <PageMeta title={unit ? `Add Lesson – ${unit.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(-1)}>
              <ArrowLeft className="h-4 w-4" />
            </Button>
            <div>
              <h1 className="text-xl font-semibold">Create Lesson</h1>
              <p className="text-sm text-muted-foreground">Add a new lesson to this unit.</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 max-w-[120px]">
                <Label htmlFor="order">Order</Label>
                <Input id="order" type="number" min={0} {...register("order")} />
              </div>

            </div>

            {/* Objectives */}
            <div className="rounded-lg border bg-card p-6 space-y-4">
              <div className="flex items-center justify-between">
                <div>
                  <p className="text-sm font-medium">Objectives</p>
                  <p className="text-xs text-muted-foreground">What learners will achieve from this lesson.</p>
                </div>
                <Button
                  type="button"
                  variant="outline"
                  size="sm"
                  onClick={() => append({ value: "" })}
                >
                  <Plus className="h-4 w-4 mr-1" />
                  Add
                </Button>
              </div>

              {fields.length === 0 && (
                <p className="text-sm text-muted-foreground text-center py-4">
                  No objectives yet. Click Add to get started.
                </p>
              )}

              <div className="space-y-3">
                {fields.map((field, index) => (
                  <div key={field.id} className="flex items-start gap-2">
                    <div className="flex-1 space-y-1">
                      <Input
                        placeholder={`Objective ${index + 1}`}
                        {...register(`objectives.${index}.value`)}
                      />
                      <FieldError message={errors.objectives?.[index]?.value?.message} />
                    </div>
                    <Button
                      type="button"
                      variant="ghost"
                      size="icon"
                      onClick={() => remove(index)}
                      className="text-muted-foreground hover:text-destructive mt-0.5"
                    >
                      <Trash2 className="h-4 w-4" />
                    </Button>
                  </div>
                ))}
              </div>
            </div>

            <div className="flex justify-end gap-3">
              <Button type="button" variant="outline" onClick={() => navigate(-1)} disabled={loading}>
                Cancel
              </Button>
              <Button type="submit" disabled={loading}>
                {loading && <Spinner className="h-4 w-4 mr-2" />}
                Create Lesson
              </Button>
            </div>
          </form>
        </div>
      </div>
    </section>
  );
}