import * as fs from "node:fs";
import * as path from "node:path";

export interface ResolvedRule {
  name: string; // path relative to its source dir, forward-slashed
  absPath: string;
  source: "base" | "local";
}

function scan(dir: string, base = ""): { name: string; absPath: string }[] {
  const out: { name: string; absPath: string }[] = [];
  let entries: fs.Dirent[];
  try {
    entries = fs.readdirSync(dir, { withFileTypes: true });
  } catch (e) {
    const code = (e as NodeJS.ErrnoException).code;
    if (code === "ENOENT" || code === "ENOTDIR") return out;
    throw e;
  }
  for (const e of entries) {
    const rel = base ? `${base}/${e.name}` : e.name;
    if (e.isDirectory()) out.push(...scan(path.join(dir, e.name), rel));
    else if (e.isFile() && e.name.endsWith(".md")) out.push({ name: rel, absPath: path.join(dir, e.name) });
  }
  return out;
}

/** Base rules ⊕ local rules; local appended last; a same-named local rule
 *  replaces the base entry in place. Names are sorted within each source. */
export function resolveRuleFiles(baseDir: string, localDir: string): ResolvedRule[] {
  const byName = new Map<string, ResolvedRule>();
  for (const f of scan(baseDir).sort((a, b) => a.name.localeCompare(b.name)))
    byName.set(f.name, { ...f, source: "base" });
  for (const f of scan(localDir).sort((a, b) => a.name.localeCompare(b.name)))
    byName.set(f.name, { ...f, source: "local" }); // local wins, keeps insertion slot
  return [...byName.values()];
}