subcommands: prepend and append to description

This currently uses format!() which may not be the best
option. Fixes #88

cli/src/cmd/append.rs

@@ -0,0 +1,64 @@
+use crate::cmd::shared;
+use clap::{App, Arg, ArgMatches, SubCommand as ClapSubCommand};
+use failure::Fallible;
+
+use crate::cmd::{ArgMatchResult, CommandInvocation};
+
+#[derive(Debug)]
+struct Invocation {
+    task: String,
+    description: String,
+}
+
+define_subcommand! {
+    fn decorate_app<'a>(&self, app: App<'a, 'a>) -> App<'a, 'a> {
+        app.subcommand(
+            ClapSubCommand::with_name("append").about("appends to a task description")
+                .arg(shared::task_arg())
+                .arg(
+                Arg::with_name("description")
+                    .help("extra task description")
+                    .required(true),
+            ),
+        )
+    }
+    fn arg_match<'a>(&self, matches: &ArgMatches<'a>) -> ArgMatchResult {
+        match matches.subcommand() {
+            ("append", Some(matches)) => ArgMatchResult::Ok(Box::new(Invocation {
+                task: matches.value_of("task").unwrap().into(),
+                description: matches.value_of("description").unwrap().into(),
+            })),
+            _ => ArgMatchResult::None,
+        }
+    }
+
+}
+
+subcommand_invocation! {
+    fn run(&self, command: &CommandInvocation) -> Fallible<()> {
+        let mut replica = command.get_replica()?;
+        let task = shared::get_task(&mut replica, &self.task)?;
+
+        let mut task = task.into_mut(&mut replica);
+
+        let new_description = format!("{} {}", task.get_description(), self.description.clone());
+        task.set_description(new_description)?;
+        println!("appended to task {}", task.get_uuid());
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn parse_command() {
+        with_subcommand_invocation!(
+            vec!["task", "append", "1", "foo bar"],
+            |inv: &Invocation| {
+                assert_eq!(inv.description, "foo bar".to_string());
+            }
+        );
+    }
+}