export type CourseProgress = {
  lastLessonId: string | null;
  completedLessonIds: string[];
};

const STORAGE_KEY = "acve.local-progress.v1";
const PROGRESS_UPDATED_EVENT = "acve:progress-updated";

type ProgressStore = Record<string, Record<string, CourseProgress>>;

const defaultProgress: CourseProgress = {
  lastLessonId: null,
  completedLessonIds: [],
};

const isBrowser = () => typeof window !== "undefined";

const readStore = (): ProgressStore => {
  if (!isBrowser()) return {};

  const raw = window.localStorage.getItem(STORAGE_KEY);
  if (!raw) return {};

  try {
    return JSON.parse(raw) as ProgressStore;
  } catch {
    return {};
  }
};

const writeStore = (store: ProgressStore) => {
  if (!isBrowser()) return;
  window.localStorage.setItem(STORAGE_KEY, JSON.stringify(store));
  window.dispatchEvent(new Event(PROGRESS_UPDATED_EVENT));
};

const getOrCreateProgress = (store: ProgressStore, userId: string, courseSlug: string) => {
  if (!store[userId]) {
    store[userId] = {};
  }
  if (!store[userId][courseSlug]) {
    store[userId][courseSlug] = { ...defaultProgress };
  }
  return store[userId][courseSlug];
};

export const getCourseProgress = (userId: string, courseSlug: string): CourseProgress => {
  const store = readStore();
  return store[userId]?.[courseSlug] ?? { ...defaultProgress };
};

export const getCourseProgressPercent = (
  userId: string,
  courseSlug: string,
  totalLessons: number,
): number => {
  if (totalLessons <= 0) return 0;
  const progress = getCourseProgress(userId, courseSlug);
  return Math.round((progress.completedLessonIds.length / totalLessons) * 100);
};

export const setLastLesson = (userId: string, courseSlug: string, lessonId: string) => {
  const store = readStore();
  const progress = getOrCreateProgress(store, userId, courseSlug);
  progress.lastLessonId = lessonId;
  writeStore(store);
};

export const markLessonComplete = (userId: string, courseSlug: string, lessonId: string) => {
  const store = readStore();
  const progress = getOrCreateProgress(store, userId, courseSlug);
  if (!progress.completedLessonIds.includes(lessonId)) {
    progress.completedLessonIds = [...progress.completedLessonIds, lessonId];
  }
  progress.lastLessonId = lessonId;
  writeStore(store);
};

export const clearCourseProgress = (userId: string, courseSlug: string) => {
  const store = readStore();
  if (!store[userId]) return;
  delete store[userId][courseSlug];
  writeStore(store);
};

export const progressUpdatedEventName = PROGRESS_UPDATED_EVENT;