Refactor command-line handling into modules per subcommands

cli/src/cmd/mod.rs

@@ -0,0 +1,69 @@
+use clap::{App, ArgMatches};
+use failure::{Error, Fallible};
+use std::path::Path;
+use taskchampion::{taskstorage, Replica};
+
+#[macro_use]
+mod macros;
+
+mod add;
+mod gc;
+mod list;
+mod pending;
+
+/// Get a list of all subcommands in this crate
+pub(crate) fn subcommands() -> Vec<Box<dyn SubCommand>> {
+    vec![add::cmd(), gc::cmd(), list::cmd(), pending::cmd()]
+}
+
+/// The result of a [`crate::cmd::SubCommand::arg_match`] call
+pub(crate) enum ArgMatchResult {
+    /// No match
+    None,
+
+    /// A good match
+    Ok(Box<dyn SubCommandInvocation>),
+
+    /// A match, but an issue with the command line
+    Err(Error),
+}
+
+/// A subcommand represents a defined subcommand, and is typically a singleton.
+pub(crate) trait SubCommand {
+    /// Decorate the given [`clap::App`] appropriately for this subcommand
+    fn decorate_app<'a>(&self, app: App<'a, 'a>) -> App<'a, 'a>;
+
+    /// If this ArgMatches is for this command, return an appropriate invocation.
+    fn arg_match<'a>(&self, matches: &ArgMatches<'a>) -> ArgMatchResult;
+}
+
+/// A subcommand invocation is specialized to a subcommand
+pub(crate) trait SubCommandInvocation: std::fmt::Debug {
+    fn run(&self, command: &CommandInvocation) -> Fallible<()>;
+
+    // tests use downcasting, which requires a function to cast to Any
+    #[cfg(test)]
+    fn as_any(&self) -> &dyn std::any::Any;
+}
+
+/// A command invocation contains all of the necessary regarding a single invocation of the CLI.
+#[derive(Debug)]
+pub struct CommandInvocation {
+    pub(crate) subcommand: Box<dyn SubCommandInvocation>,
+}
+
+impl CommandInvocation {
+    pub(crate) fn new(subcommand: Box<dyn SubCommandInvocation>) -> Self {
+        Self { subcommand }
+    }
+
+    pub fn run(self) -> Fallible<()> {
+        self.subcommand.run(&self)
+    }
+
+    fn get_replica(&self) -> Replica {
+        Replica::new(Box::new(
+            taskstorage::KVStorage::new(Path::new("/tmp/tasks")).unwrap(),
+        ))
+    }
+}