Refactor to break out scheduler

crates/lib/src/metars/utils.rs

@@ -0,0 +1,113 @@
+use crate::error::{CoreError, CoreErrorKind, CoreResult};
+use chrono::{Datelike, NaiveDate, Utc};
+
+pub fn parse_metar_time(observation_time: &str) -> CoreResult<String> {
+  if observation_time.len() != 7 {
+    return Err(CoreError::new(
+      CoreErrorKind::InvalidInput,
+      format!("Unable to parse observation time in {}", observation_time),
+    ));
+  }
+  let observation_day = match observation_time[0..2].parse::<u32>() {
+    Ok(day) => day,
+    Err(err) => return Err(err.into()),
+  };
+  let observation_hour = match observation_time[2..4].parse::<u32>() {
+    Ok(hour) => hour,
+    Err(err) => return Err(err.into()),
+  };
+  let observation_minute = match observation_time[4..6].parse::<u32>() {
+    Ok(minute) => minute,
+    Err(err) => return Err(err.into()),
+  };
+  let current_time = Utc::now().naive_utc();
+  let current_year = current_time.year();
+  let current_month = current_time.month();
+  let candidate_date = NaiveDate::from_ymd_opt(current_year, current_month, observation_day)
+    .ok_or_else(|| {
+      CoreError::new(
+        CoreErrorKind::InvalidInput,
+        format!(
+          "Invalid date with day {} for current month",
+          observation_day
+        ),
+      )
+    })?;
+  let candidate_date = match candidate_date.and_hms_opt(observation_hour, observation_minute, 0) {
+    Some(date) => date,
+    None => {
+      return Err(CoreError::new(
+        CoreErrorKind::InvalidInput,
+        format!(
+          "Invalid time for time '{}': hour {}, minute {}",
+          observation_time, observation_hour, observation_minute
+        ),
+      ));
+    }
+  };
+
+  let obs_datetime = if candidate_date > current_time {
+    // Subtract one month. (Handle year rollover carefully.)
+    let (month, year) = if current_month == 1 {
+      (12, current_year - 1)
+    } else {
+      (current_month - 1, current_year)
+    };
+
+    let adjusted_date = NaiveDate::from_ymd_opt(year, month, observation_day).ok_or_else(|| {
+      CoreError::new(
+        CoreErrorKind::InvalidInput,
+        format!(
+          "Invalid date with day {} for month {}",
+          observation_day, month
+        ),
+      )
+    })?;
+    adjusted_date
+      .and_hms_opt(observation_hour, observation_minute, 0)
+      .unwrap()
+  } else {
+    candidate_date
+  };
+  Ok(obs_datetime.format("%Y-%m-%dT%H:%M:00Z").to_string())
+}
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+  use chrono::NaiveDateTime;
+
+  #[test]
+  fn test_parse_metar_time() {
+    for day in 1..=31 {
+      for hour in 0..24 {
+        for minute in 0..60 {
+          // METAR form "DDHHMMZ"
+          let obs_time = format!("{:02}{:02}{:02}Z", day, hour, minute);
+          let result = parse_metar_time(&obs_time);
+          match result {
+            Ok(datetime_str) => {
+              // "YYYY-MM-DDTHH:MM:00Z"
+              assert_eq!(
+                datetime_str.len(),
+                20,
+                "Unexpected length for input {} yielded {}",
+                obs_time,
+                datetime_str
+              );
+              // Remove the trailing 'Z' and parse
+              let trimmed = &datetime_str[..19];
+              NaiveDateTime::parse_from_str(trimmed, "%Y-%m-%dT%H:%M:%S").unwrap_or_else(|e| {
+                panic!(
+                  "Parsing '{}' from input {} failed: {}",
+                  trimmed, obs_time, e
+                )
+              });
+            }
+            Err(_err) => {}
+          }
+        }
+      }
+    }
+  }
+}