// Phase 6A §3 — loads a module_activity's Markdown content file. Same read-only cache pattern
// as curriculum.js (scenarios/bundles): loaded from disk, cached, exposed via a reload for
// tests/dev. Long-form lesson prose lives in git-tracked Markdown (content/root/...), not
// Postgres — see docs/COURSE_CONTENT_MODEL.md for why.
//
// A single convention splits shared (self-paced-visible) content from instructor-only content
// in the SAME file, instead of two files that can drift apart: everything before the first
// "## Instructor Notes" heading is shared; that heading and everything after it is
// instructor-only. Self-paced/student responses never include the instructor_notes field
// regardless of any request parameter — this mirrors the RBAC convention used everywhere else
// in this codebase (identity decides visibility, never a client-supplied flag).

const fs = require('fs');
const path = require('path');

// Same convention as curriculum.js's SCENARIOS_DIR: one level up from src/, where the
// Dockerfile COPYs both scenarios/ and content/ (see platform/api/Dockerfile) — 'content/...'
// paths stored in module_activities.content_path resolve against this, not the actual repo
// root, since that's what the running image actually has on disk.
const ROOT_DIR = process.env.CONTENT_ROOT_DIR || path.join(__dirname, '..');
const INSTRUCTOR_HEADING = /\n## Instructor Notes\b/;

const cache = new Map(); // content_path -> { shared, instructorNotes } | null (missing file)

function splitContent(raw) {
  const match = raw.match(INSTRUCTOR_HEADING);
  if (!match) return { shared: raw.trim(), instructorNotes: null };
  return {
    shared: raw.slice(0, match.index).trim(),
    instructorNotes: raw.slice(match.index).replace(/^\n/, '').trim(),
  };
}

// contentPath is always a repo-relative path (module_activities.content_path, e.g.
// 'content/root/root-10-.../m01-health-probes/01-lesson-....md') — resolved against the repo
// root, never against anything a request supplies, so there's no path-traversal surface here.
function loadContent(contentPath) {
  if (!contentPath) return null;
  if (cache.has(contentPath)) return cache.get(contentPath);
  const abs = path.join(ROOT_DIR, contentPath);
  let result = null;
  try {
    result = splitContent(fs.readFileSync(abs, 'utf8'));
  } catch {
    result = null; // missing file — a PARTIAL/PLANNED activity may legitimately have no content yet
  }
  cache.set(contentPath, result);
  return result;
}

function reloadCache() {
  cache.clear();
}

module.exports = { loadContent, reloadCache };