/**
 * Format a byte count into a human-readable string.
 *
 * @example formatBytes(1536) // '1.5 KB'
 * @example formatBytes(0)    // '0 B'
 */
export function formatBytes(bytes: number): string {
  if (bytes <= 0) return '0 B';
  const k = 1024;
  const sizes = ['B', 'KB', 'MB', 'GB', 'TB'];
  const i = Math.floor(Math.log(bytes) / Math.log(k));
  return `${parseFloat((bytes / Math.pow(k, i)).toFixed(1))} ${sizes[i]}`;
}

/**
 * Approximate token count for a text string.
 *
 * Uses a word-count × 1.3 heuristic (typical for English text with LLM tokenizers).
 */
export function estimateTokens(text: string): number {
  const trimmed = text.trim();
  if (!trimmed) return 0;
  return Math.ceil(trimmed.split(/\s+/).length * 1.3);
}

/**
 * Best-effort model context window lookup based on model name.
 *
 * Checks for common context window markers in the model name string.
 * Falls back to 4096 if no marker is found.
 */
export function getModelContextWindow(modelName: string): number {
  const n = modelName.toLowerCase();
  if (n.includes('128k')) return 128_000;
  if (n.includes('64k')) return 64_000;
  if (n.includes('32k')) return 32_000;
  if (n.includes('16k')) return 16_000;
  if (n.includes('8k')) return 8_000;
  return 4_096;
}

/**
 * Format a duration in seconds to a human-readable uptime string.
 *
 * @example formatUptime(90061) // '1d 1h 1m'
 * @example formatUptime(3661)  // '1h 1m'
 * @example formatUptime(120)   // '2m'
 */
export function formatUptime(seconds: number): string {
  const d = Math.floor(seconds / 86400);
  const h = Math.floor((seconds % 86400) / 3600);
  const m = Math.floor((seconds % 3600) / 60);
  if (d > 0) return `${d}d ${h}h ${m}m`;
  if (h > 0) return `${h}h ${m}m`;
  return `${m}m`;
}