1 files changed, 86 insertions, 0 deletions
diff --git a/src/trial.rs b/src/trial.rs
new file mode 100644
index 0000000..9604f62
--- /dev/null
+++ b/src/trial.rs
@@ -0,0 +1,86 @@
+use chrono::{DateTime, Local, TimeZone};
+
+use errors::DurationError;
+
+// Start timestamp on October 1 at 23h
+// Trial should be valid until November 1 00h
+
+
+const DAYS_REMAINING: u8 = 30;
+
+fn days_remaining(
+    start: DateTime<Local>,
+    now: DateTime<Local>,
+    days_available: u8,
+) -> Result<u8, DurationError> {
+    let duration = (now.date() - start.date()).num_days() as u8;
+
+    if duration > days_available {
+        Err(
+            DurationError::NegativeDuration(days_available as i32 - duration as i32)
+        )
+    } else {
+        Ok(days_available - duration)
+    }
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn days_remaining_counts_days_remaining_from_start_date() {
+        let remaining = days_remaining(
+            Local.ymd(2018, 10, 1).and_hms(23, 1, 0),
+            Local.ymd(2018, 10, 1).and_hms(23, 30, 0),
+            30,
+        );
+
+        assert_eq!(remaining, Ok(30));
+    }
+
+    #[test]
+    fn days_remaining_with_middle_date() {
+        let remaining = days_remaining(
+            Local.ymd(2018, 10, 1).and_hms(23, 1, 0),
+            Local.ymd(2018, 10, 22).and_hms(15, 0, 0),
+            30,
+        );
+
+        assert_eq!(remaining, Ok(9));
+    }
+
+    #[test]
+    fn days_remaining_on_last_day_is_0() {
+        let remaining = days_remaining(
+            Local.ymd(2018, 10, 1).and_hms(23, 1, 0),
+            Local.ymd(2018, 10, 31).and_hms(23, 30, 0),
+            30,
+        );
+
+        assert_eq!(remaining, Ok(0));
+    }
+
+    #[test]
+    fn days_remaining_on_day_following_last_day_is_negative_duration_error() {
+        let remaining = days_remaining(
+            Local.ymd(2018, 10, 1).and_hms(23, 1, 0),
+            Local.ymd(2018, 11, 1).and_hms(0, 0, 0),
+            30,
+        );
+
+        assert_eq!(remaining, Err(DurationError::NegativeDuration(-1)));
+    }
+
+    #[test]
+    fn days_remaining_after_last_day_is_negative_duration_error() {
+        let remaining = days_remaining(
+            Local.ymd(2018, 10, 1).and_hms(23, 1, 0),
+            Local.ymd(2018, 11, 5).and_hms(0, 0, 0),
+            30,
+        );
+
+        assert_eq!(remaining, Err(DurationError::NegativeDuration(-5)));
+    }
+}