loopd: five-field UTC cron matcher

Co-Authored-By: ornith-1.5-35b-a3b <agent@wntrmute.dev>

crates/loopd/src/cron.rs

@@ -0,0 +1,84 @@
+//! Five-field UTC crontab matcher (M5d spec, section 4.2). No cron crate.
+
+use bxcore::Timestamp;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum CronError {
+    Fields(String),
+}
+
+impl std::fmt::Display for CronError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            CronError::Fields(schedule) => {
+                write!(f, "cron schedule {schedule:?} is not five UTC fields")
+            }
+        }
+    }
+}
+
+impl std::error::Error for CronError {}
+
+/// Whether `schedule` matches `now` in UTC.
+pub fn due(schedule: &str, now: Timestamp) -> Result<bool, CronError> {
+    let fields: Vec<&str> = schedule.split_whitespace().collect();
+    if fields.len() != 5 {
+        return Err(CronError::Fields(schedule.to_string()));
+    }
+    let rfc = now.to_rfc3339();
+    let minute = number(&rfc, 14, 16, schedule)?;
+    let hour = number(&rfc, 11, 13, schedule)?;
+    let day = number(&rfc, 8, 10, schedule)?;
+    let month = number(&rfc, 5, 7, schedule)?;
+    let dow = {
+        let days = now.unix_millis() / 1000 / 86_400;
+        ((days + 4) % 7) as u32
+    };
+    Ok(match_field(fields[0], minute, 0, 59, schedule)?
+        && match_field(fields[1], hour, 0, 23, schedule)?
+        && match_field(fields[2], day, 1, 31, schedule)?
+        && match_field(fields[3], month, 1, 12, schedule)?
+        && match_field(fields[4], dow, 0, 6, schedule)?)
+}
+
+fn number(rfc: &str, start: usize, end: usize, schedule: &str) -> Result<u32, CronError> {
+    let piece = rfc
+        .get(start..end)
+        .ok_or_else(|| CronError::Fields(schedule.to_string()))?;
+    piece
+        .parse()
+        .map_err(|_| CronError::Fields(schedule.to_string()))
+}
+
+fn match_field(
+    field: &str,
+    value: u32,
+    min: u32,
+    max: u32,
+    schedule: &str,
+) -> Result<bool, CronError> {
+    let err = || CronError::Fields(schedule.to_string());
+    if field == "*" {
+        return Ok(true);
+    }
+    if let Some(step) = field.strip_prefix("*/") {
+        let n: u32 = step.parse().map_err(|_| err())?;
+        if n == 0 {
+            return Err(err());
+        }
+        return Ok(value.is_multiple_of(n));
+    }
+    if let Some((a, b)) = field.split_once('-') {
+        let lo: u32 = a.parse().map_err(|_| err())?;
+        let hi: u32 = b.parse().map_err(|_| err())?;
+        if lo < min || hi > max || lo > hi {
+            return Err(err());
+        }
+        return Ok(value >= lo && value <= hi);
+    }
+    let n: u32 = field.parse().map_err(|_| err())?;
+    if n < min || n > max {
+        return Err(err());
+    }
+    Ok(n == value)
+}

crates/loopd/src/lib.rs

@@ -5,6 +5,7 @@ pub mod broker_port;
 pub mod channel;
 pub mod compact;
 pub mod config;
+pub mod cron;
 pub mod http;
 pub mod llama;
 pub mod memory;