///|
fn event_text(event : @sun.Instant?) -> String {
  match event {
    Some(t) => t.to_iso_utc()
    None => "这个 UTC 日没有该事件"
  }
}

///|
fn report(date : @sun.Instant, site : @sun.Observer) -> String {
  let p = @sun.moon_position(date, site)
  let light = @sun.moon_illumination(date)
  let t = @sun.moon_times(date, site)
  let direction = if light.waxing { "盈月" } else { "亏月" }
  let visibility = if p.altitude > 0.0 {
    "月球视中心在地平线上方"
  } else {
    "月球视中心在地平线下方"
  }
  let state = match t.state {
    Crosses => "当日有升/落事件"
    AlwaysAbove => "当日始终在升落阈值上方"
    AlwaysBelow => "当日始终在升落阈值下方"
  }
  "时刻：" +
  date.to_iso_utc() +
  "\n" +
  "方位角（北起顺时针）：" +
  p.azimuth.to_string() +
  "°\n" +
  "视高度角：" +
  p.altitude.to_string() +
  "°，" +
  visibility +
  "\n" +
  "地心距离：" +
  p.distance.to_string() +
  " km\n" +
  "照明比例：" +
  light.fraction.to_string() +
  "；连续月相：" +
  light.phase.to_string() +
  "（" +
  direction +
  "）\n" +
  "亮边相对天顶角：" +
  (light.angle - p.parallactic_angle).to_string() +
  "°\n" +
  "月升：" +
  event_text(t.rise) +
  "\n月落：" +
  event_text(t.set) +
  "\n" +
  state +
  "\n"
}

///|
fn main {
  println("上海观月查询：2026-09-14 10:00 UTC（当地 18:00）")
  println(
    report(
      @sun.utc(2026, 9, 14, hour=10).unwrap(),
      @sun.observer(31.23, 121.47).unwrap(),
    ),
  )
  println("高纬对照：2022-01-14，78°N 78°E")
  println(
    report(
      @sun.utc(2022, 1, 14, hour=12).unwrap(),
      @sun.observer(78.0, 78.0).unwrap(),
    ),
  )
  println(
    "升落扫描窗口是 UTC 00:00—24:00，不是上海民用日。照明比例不是能见度，也不表示天气。",
  )
}