feat(core): add now_unix() and MonthYear

MonthYear used for card expiries; bounds 2000..=2099 are intentional.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/idfoto-core/src/lib.rs

@@ -38,6 +38,9 @@ pub use error::{IdfotoError, Result};
 pub mod ids;
 pub use ids::{AttachmentId, FieldId, ItemId};
 
+pub mod time;
+pub use time::{now_unix, MonthYear};
+
 pub mod crypto;
 pub use crypto::{decrypt, derive_master_key, encrypt, KdfParams};
 

crates/idfoto-core/src/time.rs

@@ -0,0 +1,63 @@
+//! Time helpers and the `MonthYear` type used for card expiries.
+
+use serde::{Deserialize, Serialize};
+
+/// Current Unix timestamp in seconds.
+pub fn now_unix() -> i64 {
+    chrono::Utc::now().timestamp()
+}
+
+/// Month + year (1-12 / e.g. 2026). Used for card expiries.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+pub struct MonthYear {
+    pub month: u8,
+    pub year: u16,
+}
+
+impl MonthYear {
+    pub fn new(month: u8, year: u16) -> Result<Self, &'static str> {
+        if !(1..=12).contains(&month) {
+            return Err("month must be 1..=12");
+        }
+        if year < 2000 || year > 2099 {
+            return Err("year must be 2000..=2099");
+        }
+        Ok(Self { month, year })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn now_unix_is_positive_and_recent() {
+        let t = now_unix();
+        assert!(t > 1_700_000_000); // after late 2023
+        assert!(t < 4_000_000_000); // before 2096
+    }
+
+    #[test]
+    fn month_year_constructor_rejects_bad_month() {
+        assert!(MonthYear::new(0, 2026).is_err());
+        assert!(MonthYear::new(13, 2026).is_err());
+        assert!(MonthYear::new(1, 2026).is_ok());
+        assert!(MonthYear::new(12, 2026).is_ok());
+    }
+
+    #[test]
+    fn month_year_constructor_rejects_bad_year() {
+        assert!(MonthYear::new(1, 1999).is_err());
+        assert!(MonthYear::new(1, 2100).is_err());
+        assert!(MonthYear::new(1, 2000).is_ok());
+        assert!(MonthYear::new(1, 2099).is_ok());
+    }
+
+    #[test]
+    fn month_year_round_trips_through_json() {
+        let my = MonthYear::new(7, 2030).unwrap();
+        let json = serde_json::to_string(&my).unwrap();
+        let parsed: MonthYear = serde_json::from_str(&json).unwrap();
+        assert_eq!(parsed, my);
+    }
+}