const PLACEHOLDER_RE = /\{\{(\w+)\}\}/g;

export function renderTemplate(
  body: string,
  data: Record<string, string | number | unknown>
): string {
  return body.replace(PLACEHOLDER_RE, (_, key: string) => {
    const val = data[key];
    if (val === undefined || val === null) return `{{${key}}}`;
    if (typeof val === "object") return JSON.stringify(val);
    return String(val);
  });
}

export function findMissingPlaceholders(
  body: string,
  data: Record<string, unknown>
): string[] {
  const missing: string[] = [];
  let match;
  const re = /\{\{(\w+)\}\}/g;
  while ((match = re.exec(body)) !== null) {
    const key = match[1];
    if (data[key] === undefined && !missing.includes(key)) {
      missing.push(key);
    }
  }
  return missing;
}

export const SAMPLE_PREVIEW_DATA: Record<string, unknown> = {
  user_name: "Traveler",
  context: { level: 5, recentReading: 42, exerciseDays: 3 },
  topic: "Stoic philosophy",
  week_summary: "You read 35 pages, prayed 4 days, and exercised twice.",
  reading_progress: "Currently reading page 120 of 300",
  exercise_summary: "2 exercise sessions this week",
  prayer_summary: "4 of 5 morning prayers completed",
  learning_topics: "Roman history, Latin roots",
  chronicle_context: "Chapter 3: The Long Road — 45 days on the journey",
};