Implement subtraction

1 files changed, 18 insertions, 1 deletions

diff --git a/src/timetype.rs b/src/timetype.rs
index 44b1308..e064f35 100644
--- a/src/timetype.rs
+++ b/src/timetype.rs
@@ -48,7 +48,7 @@ impl TimeType {
 
         match self {
             TT::Addition(a, b)    => add(a, b),
-            TT::Subtraction(a, b) => unimplemented!(),
+            TT::Subtraction(a, b) => sub(a, b),
             x                     => Ok(x)
         }
     }
@@ -72,6 +72,23 @@ fn add(a: Box<TimeType>, b: Box<TimeType>) -> Result<TimeType> {
     }
 }
 
+fn sub(a: Box<TimeType>, b: Box<TimeType>) -> Result<TimeType> {
+    use timetype::TimeType as TT;
+
+    match (*a, *b) {
+        (TT::Seconds(a), TT::Seconds(b)) => Ok(TT::Seconds(a - b)),
+        (TT::Minutes(a), TT::Minutes(b)) => unimplemented!(),
+        (TT::Hours(a), TT::Hours(b))     => unimplemented!(),
+        (TT::Days(a), TT::Days(b))       => unimplemented!(),
+        (TT::Weeks(a), TT::Weeks(b))     => unimplemented!(),
+        (TT::Months(a), TT::Months(b))   => unimplemented!(),
+        (TT::Years(a), TT::Years(b))     => unimplemented!(),
+        (TT::Subtraction(a, b), other)   => sub(a, b)
+            .map(Box::new)
+            .and_then(|bx| sub(bx, Box::new(other))),
+        others                           => unimplemented!(),
+    }
+}
 
 #[cfg(test)]
 mod tests {