/**
 * Wiki template expansion.
 *
 * Pure module — safe to import client-side. Replaces `{{Name}}` placeholders
 * (name trimmed, exact match on map keys) with the template body. Nested
 * placeholders expand up to at most 2 levels deep: the page body is level 0,
 * template bodies expanded from the page are level 1, templates inside those
 * are level 2, and any `{{...}}` found at level 2+ is left as literal text.
 * If a template name repeats anywhere in the current expansion chain, that
 * `{{Name}}` is left literal (cycle guard).
 */

export type TemplateMap = Record<string, string>;

const PLACEHOLDER_RE = /\{\{\s*([^{}]+?)\s*\}\}/g;

function expandLevel(
  text: string,
  templates: TemplateMap,
  depth: number,
  chain: string[],
): string {
  if (depth >= 2) return text;
  return text.replace(PLACEHOLDER_RE, (match, rawName: string) => {
    const name = rawName.trim();
    const body = templates[name];
    if (body === undefined) return match;
    if (chain.includes(name)) return match;
    return expandLevel(body, templates, depth + 1, [...chain, name]);
  });
}

export function expandTemplates(source: string, templates: TemplateMap): string {
  return expandLevel(source, templates, 0, []);
}