Add skeleton of administration commands

src/error.rs

@@ -3,6 +3,7 @@ use std::io;
 
 pub enum Error {
     Io(io::Error),
+    MultipleCommands,
 }
 
 impl From<io::Error> for Error {
@@ -17,6 +18,10 @@ impl fmt::Debug for Error {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             Error::Io(e) => writeln!(f, "Failed to set up YubiKey: {}", e)?,
+            Error::MultipleCommands => writeln!(
+                f,
+                "Only one of --generate, --identity, --list, --list-all can be specified."
+            )?,
         }
         writeln!(f)?;
         writeln!(

src/main.rs

@@ -17,11 +17,32 @@ struct PluginOptions {
         no_short
     )]
     age_plugin: Option<String>,
+
+    #[options(help = "Generate a new YubiKey identity.")]
+    generate: bool,
+
+    #[options(help = "Print the identity stored in a YubiKey slot.")]
+    identity: bool,
+
+    #[options(help = "List all age identities in connected YubiKeys.")]
+    list: bool,
+
+    #[options(help = "List all YubiKey keys that are compatible with age.", no_short)]
+    list_all: bool,
 }
 
 fn main() -> Result<(), Error> {
     let opts = PluginOptions::parse_args_default_or_exit();
 
+    if [opts.generate, opts.identity, opts.list, opts.list_all]
+        .iter()
+        .filter(|&&b| b)
+        .count()
+        > 1
+    {
+        return Err(Error::MultipleCommands);
+    }
+
     if let Some(state_machine) = opts.age_plugin {
         run_state_machine(
             &state_machine,
@@ -29,6 +50,14 @@ fn main() -> Result<(), Error> {
             || plugin::IdentityPlugin::default(),
         )?;
         Ok(())
+    } else if opts.generate {
+        todo!()
+    } else if opts.identity {
+        todo!()
+    } else if opts.list {
+        todo!()
+    } else if opts.list_all {
+        todo!()
     } else {
         // TODO: CLI identity generation
         Ok(())