/**
 * Shared utility for reordering budget table rows.
 * Recursively moves subtotal (parent) rows below their children
 * at every depth level when "subtotals on bottom" is enabled.
 *
 * The generic constraint only requires the two fields the algorithm actually
 * reads (`is_parent`, `depth`) so it works for both the budget rows (required
 * `is_parent`) and the Compare `CategoryDelta` rows (optional `is_parent`).
 */
export function reorderRows<
  T extends { is_parent?: boolean; depth?: number },
>(rows: T[], subtotalsOnTop: boolean): T[] {
  if (subtotalsOnTop) return rows;

  function reorderGroup(groupRows: T[], parentDepth: number): T[] {
    const result: T[] = [];
    let currentParent: T | null = null;
    let currentChildren: T[] = [];

    for (const row of groupRows) {
      if (row.is_parent && (row.depth ?? 0) === parentDepth) {
        // Flush previous group
        if (currentParent) {
          result.push(...reorderGroup(currentChildren, parentDepth + 1), currentParent);
          currentChildren = [];
        }
        currentParent = row;
      } else if (currentParent) {
        currentChildren.push(row);
      } else {
        result.push(row);
      }
    }
    // Flush last group
    if (currentParent) {
      result.push(...reorderGroup(currentChildren, parentDepth + 1), currentParent);
    }
    return result;
  }

  return reorderGroup(rows, 0);
}