import { readFileSync } from "node:fs";
import { join } from "node:path";

import { wikilinkTarget } from "../substrate/page-links.js";
import type { Slug } from "./types.js";

/**
 * Workspace-relative path of the maintainer-curated core-set file. Edited
 * during memory consolidation — the loader never creates or modifies it.
 */
const CORE_PAGES_RELATIVE_PATH = join("memory", "core-pages.md");

/**
 * A list line is `- <item>`; the item may be a bare slug or a `[[slug]]`
 * wikilink, optionally followed by an inline annotation. After a wikilink the
 * annotation is free-form (`- [[some-slug]] — why this matters`); after a
 * bare slug it must be introduced by a dash (`- some-slug — why this
 * matters`), so a multi-word prose line (`- two words here`) is still read as
 * the maintainer's notes, not a slug. Anything else on the line (headings,
 * prose) is ignored.
 */
const LIST_LINE = /^-\s+(?:\[\[([^\]]+)\]\](?:\s+.*)?|(\S+)(?:\s+[—–-].*)?)$/;

/** Slug-safe charset; existence against the page store is checked at lane init. */
const SLUG_SHAPE = /^[a-z0-9-/]+$/;

/**
 * Load the maintainer-curated core set from `<workspaceDir>/memory/core-pages.md`.
 *
 * The core lane answers the associative-texture gap (pages with no
 * lexical/semantic match to the message), so its membership is curated, not
 * computed. Parsing is tolerant: list lines in `- [[some-slug]]` or
 * `- some-slug` form are accepted, with optional inline annotations (see
 * {@link LIST_LINE}); headings, blank lines, and prose are skipped so the
 * maintainer can annotate the file; malformed or non-slug-shaped entries are
 * dropped, never fatal.
 *
 * Returns slugs deduped in first-seen file order — that order is the stable
 * sort the selector uses for the core prefix. A missing file yields `[]`.
 */
export function loadCoreSet(workspaceDir: string): Slug[] {
  let raw: string;
  try {
    raw = readFileSync(join(workspaceDir, CORE_PAGES_RELATIVE_PATH), "utf8");
  } catch {
    return [];
  }

  const seen = new Set<Slug>();
  const slugs: Slug[] = [];
  for (const line of raw.split("\n")) {
    const match = LIST_LINE.exec(line.trim());
    if (!match) {
      continue;
    }
    const slug =
      match[1] !== undefined
        ? wikilinkTarget(match[1])
        : (match[2] ?? "").trim();
    if (!SLUG_SHAPE.test(slug) || seen.has(slug)) {
      continue;
    }
    seen.add(slug);
    slugs.push(slug);
  }
  return slugs;
}