/**
 * System-prompt adjustment used by pi-shepherd-launched agents.
 *
 * Pi's default identity paragraph is useful for the main session, but it is
 * misleading when an agent has a more specific system-prompt body. Keep the
 * match exact so custom prompts and future Pi prompt changes are left alone.
 */

export const PI_DEFAULT_IDENTITY =
  'You are an expert coding assistant operating inside pi, a coding agent harness. You help users by reading files, executing commands, editing code, and writing new files.';

export function replacePiIdentity(systemPrompt: string, replacement: unknown): string {
  if (typeof replacement !== 'string') return systemPrompt;
  const value = replacement.trim();
  if (!value || !systemPrompt.startsWith(PI_DEFAULT_IDENTITY)) return systemPrompt;
  return value + systemPrompt.slice(PI_DEFAULT_IDENTITY.length);
}

/** Remove only Pi's built-in documentation guidance, not project context. */
export function omitPiDocumentation(systemPrompt: string): string {
  const marker = '\n\nPi documentation (read only when the user asks about pi itself';
  const start = systemPrompt.indexOf(marker);
  if (start < 0) return systemPrompt;
  const finalBullet = systemPrompt.indexOf(
    '\n- Always read pi .md files completely and follow links to related docs',
    start + marker.length
  );
  if (finalBullet >= 0) {
    const end = systemPrompt.indexOf('\n', finalBullet + 1);
    const suffix = systemPrompt.slice(end < 0 ? systemPrompt.length : end);
    return systemPrompt.slice(0, start) + (suffix.startsWith('\n\n') ? '' : '\n') + suffix;
  }
  // Keep a conservative fallback for a future Pi wording change where the
  // section is still separated from the next prompt section by a blank line.
  const end = systemPrompt.indexOf('\n\n', start + marker.length);
  if (end < 0) return systemPrompt.slice(0, start);
  return systemPrompt.slice(0, start) + systemPrompt.slice(end);
}