import { createContext, useCallback, useContext, useState } from "react";
import api from "@/utils/api.util";
import { toast } from "sonner";

const CoursesContext = createContext(null);

export function useCourses() {
  const ctx = useContext(CoursesContext);
  if (!ctx) throw new Error("useCourses must be used within a CoursesProvider");
  return ctx;
}

// ─── Initial States ───────────────────────────────────────────────────────────

const PAGINATION_INIT = {
  page: 1,
  limit: 10,
  totalRecords: 0,
  totalPages: 0,
  hasPrevPage: false,
  hasNextPage: false,
};

const BASE = "/admin/courses";

// ─── Provider ─────────────────────────────────────────────────────────────────

export function CoursesProvider({ children }) {

  // ─── State ────────────────────────────────────────────────────────────────
  const [courses, setCourses] = useState([]);
  const [course, setCourse] = useState(null);
  const [units, setUnits] = useState([]);
  const [unit, setUnit] = useState(null);
  const [lessons, setLessons] = useState([]);
  const [lesson, setLesson] = useState(null);
  const [lessonPage, setLessonPage] = useState(null);
  const [prerequisites, setPrerequisites] = useState([]);
  const [quiz, setQuiz] = useState(null);
  const [questions, setQuestions] = useState([]);
  const [assessment, setAssessment] = useState(null);
  const [completions, setCompletions] = useState(null);   // { summary, completions[] }
  const [sessions, setSessions]       = useState(null);   // { summary, sessions[] }
  const [attributes, setAttributes] = useState([]);
  const [pagination, setPagination] = useState(PAGINATION_INIT);
  const [loading, setLoading] = useState(false);

  // ─── Request wrapper ──────────────────────────────────────────────────────
  const request = useCallback(async (fn) => {
    setLoading(true);
    try {
      return await fn();
    } catch (err) {
      const message = err?.response?.data?.message ?? "Something went wrong.";
      if (err.status === 404 && message) toast.warning(message);
      else toast.error(message);
      return null;
    } finally {
      setLoading(false);
    }
  }, []);

  // ─── Paginated GET helper ─────────────────────────────────────────────────
  const paginatedGet = useCallback(
    (url, setter, params = {}) =>
      request(async () => {
        const { filters, sort, ...rest } = params;
        const { data } = await api.get(url, {
          params: {
            ...rest,
            ...(filters?.length ? { filters: JSON.stringify(filters) } : {}),
            ...(sort?.length ? { sort: JSON.stringify(sort) } : {}),
          },
        });
        const final_data = data?.data;
        setter(final_data?.data ?? []);
        setPagination(final_data?.pagination ?? PAGINATION_INIT);
        if (final_data?.attributes?.length) setAttributes(final_data.attributes);
        return data;
      }),
    [request],
  );

  // =========================================================================
  // COURSES
  // =========================================================================

  const fetchCourses = useCallback(
    (params = {}) => paginatedGet(BASE, setCourses, params),
    [paginatedGet],
  );

  const fetchCourse = useCallback(
    (courseId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}`);
        const result = data?.data?.data ?? null;
        setCourse(result);
        setUnits(result?.units ?? []);
        setPrerequisites(result?.prerequisites ?? []);
        setAssessment(result?.assessment ?? null);
        return data;
      }),
    [request],
  );

  const createCourse = useCallback(
    (payload) =>
      request(async () => {
        const { data } = await api.post(BASE, payload);
        const course = data?.data?.data ?? null;
        if (course) {
          setCourses((prev) => [course, ...prev]);
          toast.success("Course created successfully.");
        }
        return data;
      }),
    [request],
  );

  const updateCourse = useCallback(
    (courseId, payload) =>
      request(async () => {
        const { data } = await api.put(`${BASE}/${courseId}`, payload);
        const course = data?.data?.data ?? null;
        if (course) {
          setCourses((prev) => prev.map((c) => (c.course_id === courseId ? course : c)));
          setCourse(course);
          toast.success("Course updated successfully.");
        }
        return data;
      }),
    [request],
  );

  const archiveCourse = useCallback(
    (courseId) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}`);
        setCourses((prev) => prev.filter((c) => c.course_id !== courseId));
        setCourse((prev) => (prev?.course_id === courseId ? null : prev));
        toast.success("Course archived.");
        return data;
      }),
    [request],
  );

  const archiveCourses = useCallback(
    ({ ids }) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/bulk`, { data: { ids } });
        setCourses((prev) => prev.filter((c) => !ids.includes(c.course_id)));
        toast.success("Courses archived.");
        return data;
      }),
    [request],
  );

  // ── Course Archives & Restore ─────────────────────────────────────────────

  const fetchArchivedCourses = useCallback(
    (params = {}) => paginatedGet(`${BASE}/archives`, setCourses, params),
    [paginatedGet],
  );

  const fetchArchivedCourse = useCallback(
    (courseId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/archives/${courseId}`);
        const result = data?.data?.data ?? null;
        setCourse(result);
        return data;
      }),
    [request],
  );

  const restoreCourse = useCallback(
    (courseId) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/restore`);
        const result = data?.data?.data ?? null;
        if (result) {
          setCourses((prev) => prev.filter((c) => c.course_id !== courseId));
          toast.success("Course restored.");
        }
        return data;
      }),
    [request],
  );

  const restoreCourses = useCallback(
    ({ ids }) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/restore/bulk`, { ids });
        setCourses((prev) => prev.filter((c) => !ids.includes(c.course_id)));
        toast.success("Courses restored.");
        return data;
      }),
    [request],
  );

  const permanentlyDeleteCourse = useCallback(
    (courseId) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/permanent`);
        setCourses((prev) => prev.filter((c) => c.course_id !== courseId));
        setCourse((prev) => (prev?.course_id === courseId ? null : prev));
        toast.success("Course permanently deleted.");
        return data;
      }),
    [request],
  );

  const permanentlyDeleteCourses = useCallback(
    ({ ids }) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/bulk/permanent`, { data: { ids } });
        setCourses((prev) => prev.filter((c) => !ids.includes(c.course_id)));
        toast.success("Courses permanently deleted.");
        return data;
      }),
    [request],
  );

  const fetchCoursePermanentDeleteImpact = useCallback(
    (courseId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/permanent-delete-impact`);
        const { unitCount, lessonCount } = data?.data ?? {};
        return [
          { label: "unit(s)", count: unitCount ?? 0 },
          { label: "lesson(s)", count: lessonCount ?? 0 },
        ];
      }),
    [request],
  );

  // =========================================================================
  // PREREQUISITES
  // =========================================================================

  const fetchPrerequisites = useCallback(
    (courseId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/prerequisites`);
        const result = data?.data?.data ?? [];
        setPrerequisites(result);
        return data;
      }),
    [request],
  );

  const syncPrerequisites = useCallback(
    (courseId, prerequisites) =>
      request(async () => {
        const { data } = await api.put(`${BASE}/${courseId}/prerequisites`, { prerequisites });
        setPrerequisites(prerequisites);
        toast.success("Prerequisites updated.");
        return data;
      }),
    [request],
  );

  // =========================================================================
  // UNITS
  // =========================================================================

  const fetchUnits = useCallback(
    (courseId, params = {}) => {
      const mergeQuiz = (incoming) =>
        setUnits((prev) => {
          if (!prev.length) return incoming;
          const prevMap = Object.fromEntries(prev.map((u) => [u.unit_id, u]));
          return incoming.map((u) => {
            const old = prevMap[u.unit_id];
            return {
              ...u,
              quiz:    u.quiz    ?? old?.quiz    ?? null,
              quiz_id: u.quiz_id ?? old?.quiz_id ?? null,
            };
          });
        });
      return paginatedGet(`${BASE}/${courseId}/units`, mergeQuiz, params);
    },
    [paginatedGet],
  );

  const fetchUnit = useCallback(
    (courseId, unitId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/units/${unitId}`);
        const result = data?.data?.data ?? null;
        setUnit(result);
        setLessons(result?.lessons ?? []);
        setQuiz(result?.quiz ?? null);
        return data;
      }),
    [request],
  );

  const createUnit = useCallback(
    (courseId, payload) =>
      request(async () => {
        const { data } = await api.post(`${BASE}/${courseId}/units`, payload);
        const unit = data?.data?.data ?? null;
        if (unit) {
          setUnits((prev) => [...prev, unit]);
          toast.success("Unit created successfully.");
        }
        return data;
      }),
    [request],
  );

  const updateUnit = useCallback(
    (courseId, unitId, payload) =>
      request(async () => {
        const { data } = await api.put(`${BASE}/${courseId}/units/${unitId}`, payload);
        const unit = data?.data?.data ?? null;
        if (unit) {
          setUnits((prev) => prev.map((u) => (u.unit_id === unitId ? unit : u)));
          setUnit(unit);
          toast.success("Unit updated successfully.");
        }
        return data;
      }),
    [request],
  );

  const archiveUnit = useCallback(
    (courseId, unitId) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/units/${unitId}`);
        setUnits((prev) => prev.filter((u) => u.unit_id !== unitId));
        setUnit((prev) => (prev?.unit_id === unitId ? null : prev));
        toast.success("Unit archived.");
        return data;
      }),
    [request],
  );

  const archiveUnits = useCallback(
    (courseId, { ids }) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/units/bulk`, { data: { ids } });
        setUnits((prev) => prev.filter((u) => !ids.includes(u.unit_id)));
        toast.success("Units archived.");
        return data;
      }),
    [request],
  );

  // ── Unit Archives & Restore ───────────────────────────────────────────────

  const fetchArchivedUnits = useCallback(
    (courseId, params = {}) =>
      paginatedGet(`${BASE}/${courseId}/units/archives`, setUnits, params),
    [paginatedGet],
  );

  const fetchArchivedUnit = useCallback(
    (courseId, unitId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/units/archives/${unitId}`);
        const result = data?.data?.data ?? null;
        setUnit(result);
        return data;
      }),
    [request],
  );

  const restoreUnit = useCallback(
    (courseId, unitId) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/units/${unitId}/restore`);
        const result = data?.data?.data ?? null;
        if (result) {
          setUnits((prev) => prev.filter((u) => u.unit_id !== unitId));
          toast.success("Unit restored.");
        }
        return data;
      }),
    [request],
  );

  const restoreUnits = useCallback(
    (courseId, { ids }) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/units/restore/bulk`, { ids } );
        setUnits((prev) => prev.filter((u) => !ids.includes(u.unit_id)));
        toast.success("Units restored.");
        return data;
      }),
    [request],
  );

  const permanentlyDeleteUnit = useCallback(
    (courseId, unitId) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/units/${unitId}/permanent`);
        setUnits((prev) => prev.filter((u) => u.unit_id !== unitId));
        setUnit((prev) => (prev?.unit_id === unitId ? null : prev));
        toast.success("Unit permanently deleted.");
        return data;
      }),
    [request],
  );

  const permanentlyDeleteUnits = useCallback(
    (courseId, { ids }) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/units/bulk/permanent`, { data: { ids } });
        setUnits((prev) => prev.filter((u) => !ids.includes(u.unit_id)));
        toast.success("Units permanently deleted.");
        return data;
      }),
    [request],
  );

  const fetchUnitPermanentDeleteImpact = useCallback(
    (courseId, unitId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/units/${unitId}/permanent-delete-impact`);
        const { lessonCount } = data?.data ?? {};
        return [{ label: "lesson(s)", count: lessonCount ?? 0 }];
      }),
    [request],
  );

  // =========================================================================
  // UNIT QUIZ
  // =========================================================================

  const fetchQuiz = useCallback(
    (courseId, unitId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/units/${unitId}/quiz`);
        const result = data?.data?.data ?? null;
        setQuiz(result);
        setQuestions(result?.questions ?? []);
        return data;
      }),
    [request],
  );

  const createQuiz = useCallback(
    (courseId, unitId, payload) =>
      request(async () => {
        const { data } = await api.post(`${BASE}/${courseId}/units/${unitId}/quiz`, payload);
        const result = data?.data?.data ?? null;
        if (result) {
          setQuiz(result);
          toast.success("Quiz created.");
        }
        return data;
      }),
    [request],
  );

  const updateQuiz = useCallback(
    (courseId, unitId, quizId, payload) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/units/${unitId}/quiz/${quizId}`, payload);
        const result = data?.data?.data ?? null;
        if (result) {
          setQuiz(result);
          toast.success("Quiz updated.");
        }
        return data;
      }),
    [request],
  );

  const deleteQuiz = useCallback(
    (courseId, unitId, quizId, deletedBy) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/units/${unitId}/quiz/${quizId}`, { data: { deletedBy } });
        setQuiz(null);
        setQuestions([]);
        toast.success("Quiz archived.");
        return data;
      }),
    [request],
  );

  // ── Quiz Archives & Restore ───────────────────────────────────────────────

  const fetchArchivedQuiz = useCallback(
    (courseId, unitId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/units/${unitId}/quiz/archives`);
        const result = data?.data?.data ?? null;
        setQuiz(result);
        return data;
      }),
    [request],
  );

  const restoreQuiz = useCallback(
    (courseId, unitId, quizId, restoredBy) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/units/${unitId}/quiz/${quizId}/restore`, { restoredBy });
        const result = data?.data?.data ?? null;
        if (result) {
          setQuiz(result);
          toast.success("Quiz restored.");
        }
        return data;
      }),
    [request],
  );

  // =========================================================================
  // QUIZ QUESTIONS
  // =========================================================================

  const fetchQuizQuestions = useCallback(
    (courseId, unitId, quizId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/units/${unitId}/quiz/${quizId}/questions`);
        const result = data?.data?.data ?? [];
        setQuestions(result);
        return data;
      }),
    [request],
  );

  const createQuizQuestion = useCallback(
    (courseId, unitId, quizId, payload) =>
      request(async () => {
        const { data } = await api.post(`${BASE}/${courseId}/units/${unitId}/quiz/${quizId}/questions`, payload);
        const result = data?.data?.data ?? null;
        if (result) {
          setQuestions((prev) => [...prev, result]);
          toast.success("Question added.");
        }
        return data;
      }),
    [request],
  );

  const updateQuizQuestion = useCallback(
    (courseId, unitId, quizId, questionId, payload) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/units/${unitId}/quiz/${quizId}/questions/${questionId}`, payload);
        const result = data?.data?.data ?? null;
        if (result) {
          setQuestions((prev) => prev.map((q) => (q.question_id === questionId ? result : q)));
          toast.success("Question updated.");
        }
        return data;
      }),
    [request],
  );

  const bulkSyncQuizQuestions = useCallback(
    (courseId, unitId, quizId, questions, updatedBy) =>
      request(async () => {
        const { data } = await api.put(`${BASE}/${courseId}/units/${unitId}/quiz/${quizId}/questions/bulk-sync`, { questions, updatedBy });
        const result = data?.data?.data ?? [];
        setQuestions(result);
        toast.success("Quiz saved.");
        return data;
      }),
    [request],
  );

  const deleteQuizQuestion = useCallback(
    (courseId, unitId, quizId, questionId, deletedBy) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/units/${unitId}/quiz/${quizId}/questions/${questionId}`, { data: { deletedBy } });
        setQuestions((prev) => prev.filter((q) => q.question_id !== questionId));
        toast.success("Question archived.");
        return data;
      }),
    [request],
  );

  const bulkArchiveQuizQuestions = useCallback(
    (courseId, unitId, quizId, ids, deletedBy) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/units/${unitId}/quiz/${quizId}/questions/bulk`, { data: { ids, deletedBy } });
        setQuestions((prev) => prev.filter((q) => !ids.includes(q.question_id)));
        toast.success("Questions archived.");
        return data;
      }),
    [request],
  );

  // ── Quiz Question Archives & Restore ─────────────────────────────────────

  const fetchArchivedQuizQuestion = useCallback(
    (courseId, unitId, quizId, questionId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/units/${unitId}/quiz/${quizId}/questions/archives/${questionId}`);
        return data;
      }),
    [request],
  );

  const restoreQuizQuestion = useCallback(
    (courseId, unitId, quizId, questionId, restoredBy) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/units/${unitId}/quiz/${quizId}/questions/${questionId}/restore`, { restoredBy });
        toast.success("Question restored.");
        return data;
      }),
    [request],
  );

  const bulkRestoreQuizQuestions = useCallback(
    (courseId, unitId, quizId, ids, restoredBy) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/units/${unitId}/quiz/${quizId}/questions/restore/bulk`, { ids, restoredBy });
        toast.success("Questions restored.");
        return data;
      }),
    [request],
  );

  // =========================================================================
  // LESSONS
  // =========================================================================

  const fetchLessons = useCallback(
    (courseId, unitId, params = {}) =>
      paginatedGet(`${BASE}/${courseId}/units/${unitId}/lessons`, setLessons, params),
    [paginatedGet],
  );

  const fetchLesson = useCallback(
    (courseId, unitId, lessonId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/units/${unitId}/lessons/${lessonId}`);
        const result = data?.data?.data ?? null;
        setLesson(result);
        setLessonPage(result?.page ?? null);
        return data;
      }),
    [request],
  );

  const createLesson = useCallback(
    (courseId, unitId, payload) =>
      request(async () => {
        const { data } = await api.post(`${BASE}/${courseId}/units/${unitId}/lessons`, payload);
        const lesson = data?.data?.data ?? null;
        if (lesson) {
          setLessons((prev) => [...prev, lesson]);
          toast.success("Lesson created successfully.");
        }
        return data;
      }),
    [request],
  );

  const updateLesson = useCallback(
    (courseId, unitId, lessonId, payload) =>
      request(async () => {
        const { data } = await api.put(`${BASE}/${courseId}/units/${unitId}/lessons/${lessonId}`, payload);
        const lesson = data?.data?.data ?? null;
        if (lesson) {
          setLessons((prev) => prev.map((l) => (l.lesson_id === lessonId ? lesson : l)));
          setLesson(lesson);
          toast.success("Lesson updated successfully.");
        }
        return data;
      }),
    [request],
  );

  const archiveLesson = useCallback(
    (courseId, unitId, lessonId) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/units/${unitId}/lessons/${lessonId}`);
        setLessons((prev) => prev.filter((l) => l.lesson_id !== lessonId));
        setLesson((prev) => (prev?.lesson_id === lessonId ? null : prev));
        toast.success("Lesson archived.");
        return data;
      }),
    [request],
  );

  const archiveLessons = useCallback(
    (courseId, unitId, { ids }) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/units/${unitId}/lessons/bulk`, { data: { ids } });
        setLessons((prev) => prev.filter((l) => !ids.includes(l.lesson_id)));
        toast.success("Lessons archived.");
        return data;
      }),
    [request],
  );

  // ── Lesson Archives & Restore ─────────────────────────────────────────────

  const fetchArchivedLessons = useCallback(
    (courseId, unitId, params = {}) =>
      paginatedGet(`${BASE}/${courseId}/units/${unitId}/lessons/archives`, setLessons, params),
    [paginatedGet],
  );

  const fetchArchivedLesson = useCallback(
    (courseId, unitId, lessonId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/units/${unitId}/lessons/archives/${lessonId}`);
        const result = data?.data?.data ?? null;
        setLesson(result);
        return data;
      }),
    [request],
  );

  const restoreLesson = useCallback(
    (courseId, unitId, lessonId) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/units/${unitId}/lessons/${lessonId}/restore`);
        const result = data?.data?.data ?? null;
        if (result) {
          setLessons((prev) => prev.filter((l) => l.lesson_id !== lessonId));
          toast.success("Lesson restored.");
        }
        return data;
      }),
    [request],
  );

  const restoreLessons = useCallback(
    (courseId, unitId, { ids }) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/units/${unitId}/lessons/restore/bulk`, { ids });
        setLessons((prev) => prev.filter((l) => !ids.includes(l.lesson_id)));
        toast.success("Lessons restored.");
        return data;
      }),
    [request],
  );

  const permanentlyDeleteLesson = useCallback(
    (courseId, unitId, lessonId) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/units/${unitId}/lessons/${lessonId}/permanent`);
        setLessons((prev) => prev.filter((l) => l.lesson_id !== lessonId));
        setLesson((prev) => (prev?.lesson_id === lessonId ? null : prev));
        toast.success("Lesson permanently deleted.");
        return data;
      }),
    [request],
  );

  const permanentlyDeleteLessons = useCallback(
    (courseId, unitId, { ids }) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/units/${unitId}/lessons/bulk/permanent`, { data: { ids } });
        setLessons((prev) => prev.filter((l) => !ids.includes(l.lesson_id)));
        toast.success("Lessons permanently deleted.");
        return data;
      }),
    [request],
  );

  // =========================================================================
  // LESSON PAGE
  // =========================================================================

  const fetchLessonPage = useCallback(
    (courseId, unitId, lessonId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/units/${unitId}/lessons/${lessonId}/page`);
        const page = data?.data?.data ?? null;
        setLessonPage(page);
        return data;
      }),
    [request],
  );

  const saveLessonPage = useCallback(
    (courseId, unitId, lessonId, payload) =>
      request(async () => {
        const { data } = await api.put(`${BASE}/${courseId}/units/${unitId}/lessons/${lessonId}/page`, payload);
        const page = data?.data?.data ?? null;
        if (page) {
          setLessonPage(page);
          toast.success("Lesson page saved.");
        }
        return data;
      }),
    [request],
  );

  // =========================================================================
  // COURSE ASSESSMENT
  // =========================================================================

  const fetchAssessment = useCallback(
    (courseId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/assessment`);
        const result = data?.data?.data ?? null;
        setAssessment(result);
        setQuestions(result?.questions ?? []);
        return data;
      }),
    [request],
  );

  const createAssessment = useCallback(
    (courseId, payload) =>
      request(async () => {
        const { data } = await api.post(`${BASE}/${courseId}/assessment`, payload);
        const result = data?.data?.data ?? null;
        if (result) {
          setAssessment(result);
          toast.success("Assessment created.");
        }
        return data;
      }),
    [request],
  );

  const updateAssessment = useCallback(
    (courseId, assessmentId, payload) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/assessment/${assessmentId}`, payload);
        const result = data?.data?.data ?? null;
        if (result) {
          setAssessment(result);
          toast.success("Assessment updated.");
        }
        return data;
      }),
    [request],
  );

  const deleteAssessment = useCallback(
    (courseId, assessmentId, deletedBy) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/assessment/${assessmentId}`, { data: { deletedBy } });
        setAssessment(null);
        setQuestions([]);
        toast.success("Assessment archived.");
        return data;
      }),
    [request],
  );

  // ── Assessment Archives & Restore ─────────────────────────────────────────

  const fetchArchivedAssessment = useCallback(
    (courseId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/assessment/archives`);
        const result = data?.data?.data ?? null;
        setAssessment(result);
        return data;
      }),
    [request],
  );

  const restoreAssessment = useCallback(
    (courseId, assessmentId, restoredBy) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/assessment/${assessmentId}/restore`, { restoredBy });
        const result = data?.data?.data ?? null;
        if (result) {
          setAssessment(result);
          toast.success("Assessment restored.");
        }
        return data;
      }),
    [request],
  );

  // =========================================================================
  // ASSESSMENT QUESTIONS
  // =========================================================================

  const fetchAssessmentQuestions = useCallback(
    (courseId, assessmentId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/assessment/${assessmentId}/questions`);
        const result = data?.data?.data ?? [];
        setQuestions(result);
        return data;
      }),
    [request],
  );

  const createAssessmentQuestion = useCallback(
    (courseId, assessmentId, payload) =>
      request(async () => {
        const { data } = await api.post(`${BASE}/${courseId}/assessment/${assessmentId}/questions`, payload);
        const result = data?.data?.data ?? null;
        if (result) {
          setQuestions((prev) => [...prev, result]);
          toast.success("Question added.");
        }
        return data;
      }),
    [request],
  );

  const updateAssessmentQuestion = useCallback(
    (courseId, assessmentId, questionId, payload) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/assessment/${assessmentId}/questions/${questionId}`, payload);
        const result = data?.data?.data ?? null;
        if (result) {
          setQuestions((prev) => prev.map((q) => (q.question_id === questionId ? result : q)));
          toast.success("Question updated.");
        }
        return data;
      }),
    [request],
  );

  const bulkSyncAssessmentQuestions = useCallback(
    (courseId, assessmentId, questions, updatedBy) =>
      request(async () => {
        const { data } = await api.put(`${BASE}/${courseId}/assessment/${assessmentId}/questions/bulk-sync`, { questions, updatedBy });
        const result = data?.data?.data ?? [];
        setQuestions(result);
        toast.success("Assessment saved.");
        return data;
      }),
    [request],
  );

  const deleteAssessmentQuestion = useCallback(
    (courseId, assessmentId, questionId, deletedBy) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/assessment/${assessmentId}/questions/${questionId}`, { data: { deletedBy } });
        setQuestions((prev) => prev.filter((q) => q.question_id !== questionId));
        toast.success("Question archived.");
        return data;
      }),
    [request],
  );

  const bulkArchiveAssessmentQuestions = useCallback(
    (courseId, assessmentId, ids, deletedBy) =>
      request(async () => {
        const { data } = await api.delete(`${BASE}/${courseId}/assessment/${assessmentId}/questions/bulk`, { data: { ids, deletedBy } });
        setQuestions((prev) => prev.filter((q) => !ids.includes(q.question_id)));
        toast.success("Questions archived.");
        return data;
      }),
    [request],
  );

  // ── Assessment Question Archives & Restore ────────────────────────────────

  const fetchArchivedAssessmentQuestion = useCallback(
    (courseId, assessmentId, questionId) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/assessment/${assessmentId}/questions/archives/${questionId}`);
        return data;
      }),
    [request],
  );

  const restoreAssessmentQuestion = useCallback(
    (courseId, assessmentId, questionId, restoredBy) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/assessment/${assessmentId}/questions/${questionId}/restore`, { restoredBy });
        toast.success("Question restored.");
        return data;
      }),
    [request],
  );

  const bulkRestoreAssessmentQuestions = useCallback(
    (courseId, assessmentId, ids, restoredBy) =>
      request(async () => {
        const { data } = await api.patch(`${BASE}/${courseId}/assessment/${assessmentId}/questions/restore/bulk`, { ids, restoredBy });
        toast.success("Questions restored.");
        return data;
      }),
    [request],
  );

  // =========================================================================
  // COMPLETIONS & SESSIONS
  // =========================================================================

  const fetchQuizCompletions = useCallback(
    (courseId, unitId, quizId) =>
      request(async () => {
        setCompletions(null);
        const { data } = await api.get(`${BASE}/${courseId}/units/${unitId}/quiz/${quizId}/completions`);
        setCompletions(data?.data ?? null);
        return data;
      }),
    [request],
  );

  const fetchAssessmentCompletions = useCallback(
    (courseId, assessmentId) =>
      request(async () => {
        setCompletions(null);
        const { data } = await api.get(`${BASE}/${courseId}/assessment/${assessmentId}/completions`);
        setCompletions(data?.data ?? null);
        return data;
      }),
    [request],
  );

  const fetchAssessmentSessions = useCallback(
    (courseId, assessmentId) =>
      request(async () => {
        setSessions(null);
        const { data } = await api.get(`${BASE}/${courseId}/assessment/${assessmentId}/sessions`);
        setSessions(data?.data ?? null);
        return data;
      }),
    [request],
  );

  // =========================================================================
  // COURSE PRODUCT & CATEGORIES
  // =========================================================================

  const fetchCourseProduct = useCallback(
    (courseId) => request(async () => {
      const { data } = await api.get(`/admin/products/courses/${courseId}/product`);
      return data.data ?? null;
    }), [request],
  );

  const saveCourseProduct = useCallback(
    (courseId, payload) => request(async () => {
      const { data } = await api.put(`/admin/products/courses/${courseId}/product`, payload);
      toast.success("Product listing saved.");
      return data.data ?? null;
    }), [request],
  );

  const removeCourseProduct = useCallback(
    (courseId) => request(async () => {
      await api.delete(`/admin/products/courses/${courseId}/product`);
      toast.success("Product listing removed.");
      return true;
    }), [request],
  );

  const fetchCourseCategories = useCallback(
    (courseId) => request(async () => {
      const { data } = await api.get(`/admin/products/courses/${courseId}/categories`);
      return data.data ?? [];
    }), [request],
  );

  const syncCourseCategories = useCallback(
    (courseId, categoryIds) => request(async () => {
      const { data } = await api.post(`/admin/products/courses/${courseId}/categories`, { category_ids: categoryIds });
      toast.success("Categories updated.");
      return data.data ?? [];
    }), [request],
  );

  const fetchInstructors = useCallback(
    (courseId) => request(async () => {
      const { data } = await api.get(`${BASE}/${courseId}/instructors`);
      return data.data ?? [];
    }), [request],
  );

  const syncInstructors = useCallback(
    (courseId, instructors) => request(async () => {
      await api.put(`${BASE}/${courseId}/instructors`, { instructors });
      toast.success("Instructors updated.");
    }), [request],
  );

  const fetchCourseAchievements = useCallback(
    (courseId) => request(async () => {
      const { data } = await api.get(`${BASE}/${courseId}/achievements`);
      return (data?.data?.data ?? []).map((r) => r.achievement_key);
    }), [request],
  );

  const syncCourseAchievements = useCallback(
    (courseId, achievement_keys) => request(async () => {
      await api.put(`${BASE}/${courseId}/achievements`, { achievement_keys });
      toast.success("Rewards updated.");
    }), [request],
  );

  const fetchCourseFieldValues = useCallback(
    (field) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/field-values`, { params: { field } });
        const result = data?.data ?? [];
        return result;
      }),
    [request],
  );

  const fetchUnitFieldValues = useCallback(
    (courseId, field) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/field-values`, { params: { field } });
        const result = data?.data ?? [];
        return result;
      }),
    [request],
  );

  const fetchLessonFieldValues = useCallback(
    (courseId, unitId, field) =>
      request(async () => {
        const { data } = await api.get(`${BASE}/${courseId}/units/${unitId}/field-values`, { params: { field } });
        const result = data?.data ?? [];
        return result;
      }),
    [request],
  );

  // ─── Provider value ───────────────────────────────────────────────────────
  return (
    <CoursesContext.Provider value={{
      // ── state ──────────────────────────────────────────────────────────────
      courses, course,
      units, unit,
      lessons, lesson,
      lessonPage,
      prerequisites,
      quiz,
      questions,
      assessment,
      attributes,
      pagination,
      loading,

      // ── setters ────────────────────────────────────────────────────────────
      setCourse,
      setUnit,
      setLesson,
      setLessonPage,
      setPrerequisites,
      setQuiz,
      setQuestions,
      setAssessment,
      setPagination,

      // ── courses ────────────────────────────────────────────────────────────
      fetchCourses,
      fetchCourse,
      createCourse,
      updateCourse,
      archiveCourse,
      archiveCourses,

      // ── course archives & restore ──────────────────────────────────────────
      fetchArchivedCourses,
      fetchArchivedCourse,
      restoreCourse,
      restoreCourses,
      permanentlyDeleteCourse,
      permanentlyDeleteCourses,
      fetchCoursePermanentDeleteImpact,

      // ── prerequisites ──────────────────────────────────────────────────────
      fetchPrerequisites,
      syncPrerequisites,

      // ── units ──────────────────────────────────────────────────────────────
      fetchUnits,
      fetchUnit,
      createUnit,
      updateUnit,
      archiveUnit,
      archiveUnits,

      // ── unit archives & restore ────────────────────────────────────────────
      fetchArchivedUnits,
      fetchArchivedUnit,
      restoreUnit,
      restoreUnits,
      permanentlyDeleteUnit,
      permanentlyDeleteUnits,
      fetchUnitPermanentDeleteImpact,

      // ── unit quiz ──────────────────────────────────────────────────────────
      fetchQuiz,
      createQuiz,
      updateQuiz,
      deleteQuiz,

      // ── quiz archives & restore ────────────────────────────────────────────
      fetchArchivedQuiz,
      restoreQuiz,

      // ── quiz questions ─────────────────────────────────────────────────────
      fetchQuizQuestions,
      createQuizQuestion,
      updateQuizQuestion,
      deleteQuizQuestion,
      bulkArchiveQuizQuestions,
      bulkSyncQuizQuestions,

      // ── quiz question archives & restore ───────────────────────────────────
      fetchArchivedQuizQuestion,
      restoreQuizQuestion,
      bulkRestoreQuizQuestions,

      // ── lessons ────────────────────────────────────────────────────────────
      fetchLessons,
      fetchLesson,
      createLesson,
      updateLesson,
      archiveLesson,
      archiveLessons,

      // ── lesson archives & restore ──────────────────────────────────────────
      fetchArchivedLessons,
      fetchArchivedLesson,
      restoreLesson,
      restoreLessons,
      permanentlyDeleteLesson,
      permanentlyDeleteLessons,

      // ── lesson page ────────────────────────────────────────────────────────
      fetchLessonPage,
      saveLessonPage,

      // ── completions & sessions ─────────────────────────────────────────────
      completions, sessions,
      fetchQuizCompletions,
      fetchAssessmentCompletions,
      fetchAssessmentSessions,

      // ── assessment ─────────────────────────────────────────────────────────
      fetchAssessment,
      createAssessment,
      updateAssessment,
      deleteAssessment,

      // ── assessment archives & restore ──────────────────────────────────────
      fetchArchivedAssessment,
      restoreAssessment,

      // ── assessment questions ───────────────────────────────────────────────
      fetchAssessmentQuestions,
      createAssessmentQuestion,
      updateAssessmentQuestion,
      deleteAssessmentQuestion,
      bulkArchiveAssessmentQuestions,
      bulkSyncAssessmentQuestions,

      // ── assessment question archives & restore ─────────────────────────────
      fetchArchivedAssessmentQuestion,
      restoreAssessmentQuestion,
      bulkRestoreAssessmentQuestions,

      // ── fetch field values ─────────────────────────────
      fetchCourseFieldValues,
      fetchUnitFieldValues,
      fetchLessonFieldValues,

      // ── course product & categories ────────────────────
      fetchCourseProduct,
      saveCourseProduct,
      removeCourseProduct,
      fetchCourseCategories,
      syncCourseCategories,
      fetchInstructors,
      syncInstructors,
      fetchCourseAchievements,
      syncCourseAchievements,
    }}>
      {children}
    </CoursesContext.Provider>
  );
}