// Shared date/time formatting helpers.

/**
 * 后端存储的是 UTC naive datetime（SQLite 不保留时区），
 * 序列化后无 Z/+00:00 后缀。JavaScript 对无时区字符串按本地时间处理，
 * 所以必须显式加 Z，让 Date 正确当作 UTC 解析，浏览器再转换为本地时区显示。
 */
export function toDate(iso: string): Date {
  if (iso.endsWith('Z') || /[+-]\d{2}:\d{2}$/.test(iso)) return new Date(iso)
  return new Date(iso + 'Z')
}

/** 省略当年年份的紧凑格式，用于空间受限的列表行 */
export function shortDateTime(iso?: string | null): string {
  if (!iso) return '-'
  const d = toDate(iso)
  const pad = (n: number) => String(n).padStart(2, '0')
  const now = new Date()
  if (d.getFullYear() === now.getFullYear()) {
    return `${pad(d.getMonth() + 1)}-${pad(d.getDate())} ${pad(d.getHours())}:${pad(d.getMinutes())}`
  }
  return `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())} ${pad(d.getHours())}:${pad(d.getMinutes())}`
}

export function formatDateTime(iso?: string | null): string {
  if (!iso) return '-'
  const d = toDate(iso)
  const pad = (n: number) => String(n).padStart(2, '0')
  return `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())} ${pad(d.getHours())}:${pad(d.getMinutes())}`
}

export function elapsedStr(startedAt?: string | null, completedAt?: string | null): string {
  if (!startedAt) return '-'
  const start = toDate(startedAt).getTime()
  const end = completedAt ? toDate(completedAt).getTime() : Date.now()
  const secs = Math.max(0, Math.round((end - start) / 1000))
  if (secs < 60) return `${secs}s`
  const m = Math.floor(secs / 60)
  const s = secs % 60
  if (m < 60) return `${m}m ${s}s`
  const h = Math.floor(m / 60)
  return `${h}h ${m % 60}m`
}