Add TTL expiry for transient facts

src/ttl.rs

@@ -0,0 +1,49 @@
+use anyhow::{Result, anyhow};
+use chrono::{DateTime, Duration, Utc};
+
+pub fn parse_ttl_spec(ttl: &str) -> Result<Duration> {
+    let ttl = ttl.trim();
+    if ttl.is_empty() {
+        return Err(anyhow!("ttl must not be empty"));
+    }
+
+    let (value, multiplier_seconds) = match ttl.chars().last() {
+        Some('s') | Some('S') => (&ttl[..ttl.len() - 1], 1i64),
+        Some('m') | Some('M') => (&ttl[..ttl.len() - 1], 60i64),
+        Some('h') | Some('H') => (&ttl[..ttl.len() - 1], 60i64 * 60),
+        Some('d') | Some('D') => (&ttl[..ttl.len() - 1], 60i64 * 60 * 24),
+        Some('w') | Some('W') => (&ttl[..ttl.len() - 1], 60i64 * 60 * 24 * 7),
+        _ => {
+            return Err(anyhow!(
+                "invalid ttl '{ttl}'. Use a positive duration like 30s, 15m, 1h, 7d, or 2w"
+            ));
+        }
+    };
+
+    let value: i64 = value
+        .trim()
+        .parse()
+        .map_err(|_| anyhow!("invalid ttl '{ttl}'. Duration value must be a positive integer"))?;
+    if value <= 0 {
+        return Err(anyhow!("invalid ttl '{ttl}'. Duration value must be greater than zero"));
+    }
+
+    let total_seconds = value
+        .checked_mul(multiplier_seconds)
+        .ok_or_else(|| anyhow!("invalid ttl '{ttl}'. Duration is too large"))?;
+
+    Ok(Duration::seconds(total_seconds))
+}
+
+pub fn expires_at_from_ttl(ttl: Option<&str>) -> Result<Option<DateTime<Utc>>> {
+    match ttl {
+        Some(ttl) => {
+            let duration = parse_ttl_spec(ttl)?;
+            Utc::now()
+                .checked_add_signed(duration)
+                .map(Some)
+                .ok_or_else(|| anyhow!("ttl '{ttl}' overflows supported timestamp range"))
+        }
+        None => Ok(None),
+    }
+}