Refactor command-line handling into modules per subcommands

cli/src/cmd/add.rs

@@ -0,0 +1,60 @@
+use clap::{App, Arg, ArgMatches, SubCommand as ClapSubCommand};
+use failure::{format_err, Fallible};
+use taskchampion::Status;
+use uuid::Uuid;
+
+use crate::cmd::{ArgMatchResult, CommandInvocation};
+
+#[derive(Debug)]
+struct Invocation {
+    description: String,
+}
+
+define_subcommand! {
+    fn decorate_app<'a>(&self, app: App<'a, 'a>) -> App<'a, 'a> {
+        app.subcommand(
+            ClapSubCommand::with_name("add").about("adds a task").arg(
+                Arg::with_name("description")
+                    .help("task description")
+                    .required(true),
+            ),
+        )
+    }
+
+    fn arg_match<'a>(&self, matches: &ArgMatches<'a>) -> ArgMatchResult {
+        match matches.subcommand() {
+            ("add", Some(matches)) => {
+                // TODO: .unwrap() would be safe here as description is required above
+                let description: String = match matches.value_of("description") {
+                    Some(v) => v.into(),
+                    None => return ArgMatchResult::Err(format_err!("no description provided")),
+                };
+                ArgMatchResult::Ok(Box::new(Invocation { description }))
+            }
+            _ => ArgMatchResult::None,
+        }
+    }
+}
+
+subcommand_invocation! {
+    fn run(&self, command: &CommandInvocation) -> Fallible<()> {
+        let uuid = Uuid::new_v4();
+        command
+            .get_replica()
+            .new_task(uuid, Status::Pending, self.description.clone())
+            .unwrap();
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn parse_command() {
+        with_subcommand_invocation!(vec!["task", "add", "foo bar"], |inv: &Invocation| {
+            assert_eq!(inv.description, "foo bar".to_string());
+        });
+    }
+}