Add a prediction mode

src/modes.rs

@@ -0,0 +1,40 @@
+use clap::ValueEnum;
+
+#[derive(ValueEnum, Debug, Copy, Clone, Eq, PartialEq)]
+pub enum Modes {
+    /// Perform calculations by treating stdin as a stream of time pairs separated by newlines
+    TimeTable,
+    /// Perform live tracking of the user's time until an EOF character is received.
+    Live,
+    /// Predict a user's day end time (assuming a 9 hour work day) based on the user's start time
+    /// and the duration of a user's break.
+    Prediction,
+}
+
+impl Modes {
+    /// Determine whether or not the variant supports piped input vs being used as a CLI tool
+    /// directly by a human
+    pub fn supports_piped_input(&self) -> bool {
+        match self {
+            Modes::TimeTable => true,
+            Modes::Live => false,
+            Modes::Prediction => false,
+        }
+    }
+}
+
+
+impl Default for Modes {
+    fn default() -> Self {
+        Self::TimeTable
+    }
+}
+
+impl std::fmt::Display for Modes {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.to_possible_value()
+            .expect("no values are skipped")
+            .get_name()
+            .fmt(f)
+    }
+}