Initial commit with basic Date type done

src/model.rs

@@ -0,0 +1,102 @@
+use std::collections::HashSet;
+
+use anyhow::{anyhow, bail};
+
+pub struct Date {
+    pub day: u8,
+    pub month: u8,
+    pub year: u16,
+}
+
+impl Date {
+    /// Create a day from String. Expects strings in format '06-26-2026'
+    pub fn from_string(val: &str) -> anyhow::Result<Self> {
+        let mut parts = val.split("-");
+        let month = parts
+            .next()
+            .ok_or(anyhow!("Month missing from date string"))?
+            .parse()?;
+
+        if month > 12 || month == 0 {
+            bail!("Month should be > 0 and <= 12")
+        }
+
+        let day = parts
+            .next()
+            .ok_or(anyhow!("Day missing from date string"))?
+            .parse()?;
+
+        if day == 0 {
+            bail!("Day must be > 0")
+        }
+
+        match month {
+            2 => {
+                if day > 29 {
+                    bail!("February can have a max of 29 days (on leap years)")
+                }
+            }
+            4 | 6 | 9 | 11 => {
+                if day > 30 {
+                    bail!("The provided month only has 30 days")
+                }
+            }
+            1 | 3 | 5 | 7 | 8 | 10 | 12 => {
+                if day > 31 {
+                    bail!("The provided month only has 31 days")
+                }
+            }
+            _ => unreachable!(),
+        }
+
+        let year = parts
+            .next()
+            .ok_or(anyhow!("Year missing from date string"))?
+            .parse()?;
+
+        Ok(Date { day, month, year })
+    }
+}
+
+pub struct Habit {
+    pub name: String,
+    pub days_completed: HashSet<Date>,
+}
+
+#[cfg(test)]
+mod test {
+    use crate::model::Date;
+
+    #[test]
+    fn correct_date_gets_parsed() {
+        let date = Date::from_string("06-16-2026").unwrap();
+
+        assert_eq!(date.day, 16);
+        assert_eq!(date.month, 6);
+        assert_eq!(date.year, 2026);
+
+        let date = Date::from_string("6-16-2026").unwrap();
+
+        assert_eq!(date.day, 16);
+        assert_eq!(date.month, 6);
+        assert_eq!(date.year, 2026);
+
+        let date = Date::from_string("6-6-2026").unwrap();
+
+        assert_eq!(date.day, 6);
+        assert_eq!(date.month, 6);
+        assert_eq!(date.year, 2026);
+    }
+
+    #[test]
+    fn bad_date_doesnt_get_parsed() {
+        let date = Date::from_string("-12-2026");
+        assert!(date.is_err());
+
+        let date = Date::from_string("13-01-2026");
+        assert!(date.is_err());
+
+        let date = Date::from_string("01-32-2026");
+        assert!(date.is_err());
+    }
+}