///|
struct Track {
  visible_samples : Int
  peak : @sun.Position
  peak_time : @sun.Instant
  csv : String
} derive(Debug)

///|
/// Deterministic ten-minute samples, not a photovoltaic energy model.
fn track(start : @sun.Instant, site : @sun.Observer) -> Track {
  let mut peak = @sun.sun_position(start, site)
  let mut peak_time = start
  let mut visible = 0
  let mut csv = "utc,azimuth_deg,apparent_altitude_deg\n"
  let samples = @sun.sample_observations(start, 600000.0, 144, site).unwrap()
  for sample in samples {
    let date = sample.time
    let p = sample.sun
    if p.altitude > 0.0 {
      visible += 1
    }
    if p.altitude > peak.altitude {
      peak = p
      peak_time = date
    }
    csv += date.to_iso_utc() +
      "," +
      p.azimuth.to_string() +
      "," +
      p.altitude.to_string() +
      "\n"
  }
  { visible_samples: visible, peak, peak_time, csv, }
}

///|
fn main {
  let date = @sun.utc(2026, 9, 14).unwrap()
  let site = @sun.observer(31.23, 121.47).unwrap()
  let result = track(date, site)
  println(
    "上海太阳位置轨迹，UTC 2026-09-14，每 10 分钟，共 144 点",
  )
  println(
    "太阳视中心高于 0° 的样本数：" +
    result.visible_samples.to_string(),
  )
  println("样本最高点：" + result.peak_time.to_iso_utc())
  println("最高视高度角：" + result.peak.altitude.to_string() + "°")
  println(
    "求根计算的太阳中天：" +
    @sun.sun_times(date, site).solar_noon.to_iso_utc(),
  )
  println(
    "样本最高点不等于精确中天；以下 CSV 可用于太阳路径图，不用于发电量预测。",
  )
  println(result.csv)
}