Add `trial` module, calculate days remaining

This new module will contain functions to calculate trial days.

Here we implement a function to calculate the days remaining in a trial
period.

If there are less than 0 days remaining, it returns an error result.

Couldn't use 'error-chain' because it was complaining about `Debug` and
`PartialEq` not being defined. Don't know if it's possible to implement
those traits on 'error-chain''s ErrorKind`, but it was complicated
enough that I ended up not bothering. Went with 'quick_error' instead to
create a custom error type without having to `impl` all the required
traits.

5 files changed, 104 insertions, 0 deletions

diff --git a/Cargo.toml b/Cargo.toml
index e66a57a..c5bee52 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,6 +14,7 @@ getopts = "0.2.18"
 libc = "0.2.43"
 log = "0.4.5"
 objc = "0.2.5"
+quick-error = "1.2.2"
 serde = "1.0.58"
 serde_derive = "1.0.58"
 stderrlog = "0.4.1"
diff --git a/dome_key_map.h b/dome_key_map.h
index a6e44ca..88909f0 100644
--- a/dome_key_map.h
+++ b/dome_key_map.h
@@ -6,6 +6,8 @@
 #include <stdlib.h>
 #include <stdbool.h>
 
+#define DAYS_REMAINING 30
+
 typedef enum {
   HeadphoneButton_Play,
   HeadphoneButton_Up,
diff --git a/src/errors.rs b/src/errors.rs
index beafc9f..5f09c27 100644
--- a/src/errors.rs
+++ b/src/errors.rs
@@ -5,3 +5,13 @@ error_chain! {
         Xdg(xdg::BaseDirectoriesError);
     }
 }
+
+quick_error! {
+    #[derive(Debug, PartialEq)]
+    pub enum DurationError {
+        NegativeDuration(duration: i32) {
+            description("negative duration")
+            display("negative duration: '{}'", duration)
+        }
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 801591c..8e23367 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,6 +1,7 @@
 #![recursion_limit="128"]
 
 extern crate autopilot;
+extern crate chrono;
 extern crate cocoa;
 
 #[macro_use]
@@ -20,6 +21,9 @@ extern crate log;
 extern crate objc;
 
 #[macro_use]
+extern crate quick_error;
+
+#[macro_use]
 extern crate serde_derive;
 extern crate stderrlog;
 extern crate toml;
@@ -31,6 +35,7 @@ mod config;
 mod errors;
 mod key_code;
 mod parser;
+mod trial;
 
 use parser::{Action, HeadphoneButton, MapAction, MapGroup, MapKind};
 
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)));
+    }
+}