getPeriodStart (utils/period.ts)

Utility functions for computing billing period boundaries and related checks.

// Source: https://github.com/geminimir/meterguard | License: MIT | Copyright 2025 StripeMeter Contributors
// Provided via justclaw.it.com; keep this notice with the code.
/**
 * Period and date utilities
 */

/**
 * Get the start of a billing period
 */
export function getPeriodStart(date: Date | string, periodType: 'daily' | 'monthly' = 'monthly'): string {
  const d = typeof date === 'string' ? new Date(date) : date;
  
  if (periodType === 'daily') {
    return d.toISOString().split('T')[0]; // YYYY-MM-DD
  }
  
  // Monthly: first day of month
  const year = d.getUTCFullYear();
  const month = (d.getUTCMonth() + 1).toString().padStart(2, '0');
  return `${year}-${month}-01`;
}

/**
 * Get the end of a billing period
 */
export function getPeriodEnd(periodStart: string, periodType: 'd

... (truncated -- full source via MCP)