import { extname } from "node:path";
import { loadAll, resolveInside, type LoadedCourse } from "./load";
import { extractSection } from "./markdown";

export interface CourseRepository {
  list(): LoadedCourse[];
  get(id: string): LoadedCourse | null;
  /** Re-scans the course dirs. `id` is accepted for API symmetry; a rescan is cheap and keeps overlay shadowing correct. */
  reload(id?: string): Promise<void>;
  readLessonMarkdown(courseId: string, lessonId: string): Promise<string | null>;
  /** Absolute real path if inside the course root (symlinks followed), else null. */
  resolvePath(courseId: string, relPath: string): string | null;
}

const MD = new Set([".md", ".markdown"]);

export async function createCourseRepository(courseDirs: string[]): Promise<CourseRepository> {
  let courses = await loadAll(courseDirs);
  const repo: CourseRepository = {
    list: () => courses,
    get: (id) => courses.find((c) => c.id === id) ?? null,
    async reload() {
      courses = await loadAll(courseDirs);
    },
    async readLessonMarkdown(courseId, lessonId) {
      const entry = repo.get(courseId)?.lessonIndex.get(lessonId);
      if (!entry) return null;
      const { lesson } = entry;
      const rel = lesson.type === "video" ? lesson.transcript : lesson.file;
      if (!rel || !MD.has(extname(rel).toLowerCase())) return null;
      const abs = repo.resolvePath(courseId, rel);
      if (!abs) return null;
      const text = await Bun.file(abs).text();
      return lesson.anchor ? extractSection(text, lesson.anchor) : text;
    },
    resolvePath(courseId, relPath) {
      const c = repo.get(courseId);
      return c ? resolveInside(c.root, relPath) : null;
    },
  };
  return repo;
}