1 files changed, 168 insertions, 0 deletions
diff --git a/src/arg_util.rs b/src/arg_util.rs
new file mode 100644
index 0000000..3a4c001
--- /dev/null
+++ b/src/arg_util.rs
@@ -0,0 +1,168 @@
+// arg_util.rs
+
+// *************************************************************************
+// * Copyright (C) 2019-2020 Daniel Mueller (deso@posteo.net)              *
+// *                                                                       *
+// * This program is free software: you can redistribute it and/or modify  *
+// * it under the terms of the GNU General Public License as published by  *
+// * the Free Software Foundation, either version 3 of the License, or     *
+// * (at your option) any later version.                                   *
+// *                                                                       *
+// * This program is distributed in the hope that it will be useful,       *
+// * but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+// * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+// * GNU General Public License for more details.                          *
+// *                                                                       *
+// * You should have received a copy of the GNU General Public License     *
+// * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+// *************************************************************************
+
+macro_rules! count {
+  ($head:ident) => { 1 };
+  ($head:ident, $($tail:ident),*) => {
+    1 + count!($($tail),*)
+  }
+}
+
+/// Translate an optional source into an optional destination.
+macro_rules! tr {
+  ($dst:tt, $src:tt) => {
+    $dst
+  };
+  ($dst:tt) => {};
+}
+
+macro_rules! Command {
+  ( $(#[$docs:meta])* $name:ident, [
+    $( $(#[$doc:meta])* $var:ident$(($inner:ty))? => $exec:expr, ) *
+  ] ) => {
+    $(#[$docs])*
+    #[derive(Debug, PartialEq, structopt::StructOpt)]
+    pub enum $name {
+      $(
+        $(#[$doc])*
+        $var$(($inner))?,
+      )*
+    }
+
+    #[allow(unused_qualifications)]
+    impl $name {
+      pub fn execute(
+        self,
+        ctx: &mut crate::ExecCtx<'_>,
+      ) -> crate::Result<()> {
+        match self {
+          $(
+            $name::$var$((tr!(args, $inner)))? => $exec(ctx $(,tr!(args, $inner))?),
+          )*
+        }
+      }
+    }
+  };
+}
+
+/// A macro for generating an enum with a set of simple (i.e., no
+/// parameters) variants and their textual representations.
+// TODO: Right now we hard code the derives we create. We may want to
+//       make this set configurable.
+macro_rules! Enum {
+  ( $(#[$docs:meta])* $name:ident, [ $( $var:ident => $str:expr, ) *] ) => {
+    $(#[$docs])*
+    #[derive(Clone, Copy, Debug, PartialEq)]
+    pub enum $name {
+      $(
+        $var,
+      )*
+    }
+
+    enum_int! {$name, [
+      $( $var => $str, )*
+    ]}
+  };
+}
+
+macro_rules! enum_int {
+  ( $name:ident, [ $( $var:ident => $str:expr, ) *] ) => {
+    impl $name {
+      #[allow(unused)]
+      pub fn all(&self) -> [$name; count!($($var),*) ] {
+        $name::all_variants()
+      }
+
+      pub fn all_variants() -> [$name; count!($($var),*) ] {
+        [
+          $(
+            $name::$var,
+          )*
+        ]
+      }
+
+      #[allow(unused)]
+      pub fn all_str() -> [&'static str; count!($($var),*)] {
+        [
+          $(
+            $str,
+          )*
+        ]
+      }
+    }
+
+    impl ::std::convert::AsRef<str> for $name {
+      fn as_ref(&self) -> &'static str {
+        match *self {
+          $(
+            $name::$var => $str,
+          )*
+        }
+      }
+    }
+
+    impl ::std::fmt::Display for $name {
+      fn fmt(&self, f: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result {
+        write!(f, "{}", self.as_ref())
+      }
+    }
+
+    impl ::std::str::FromStr for $name {
+      type Err = ::std::string::String;
+
+      fn from_str(s: &str) -> ::std::result::Result<Self, Self::Err> {
+        match s {
+          $(
+            $str => Ok($name::$var),
+          )*
+          _ => Err(
+            format!(
+              "expected one of {}",
+              $name::all_str().join(", "),
+             )
+           )
+        }
+      }
+    }
+  };
+}
+
+#[cfg(test)]
+mod tests {
+  Enum! {Command, [
+    Var1 => "var1",
+    Var2 => "2",
+    Var3 => "crazy",
+  ]}
+
+  #[test]
+  fn all_variants() {
+    assert_eq!(
+      Command::all_variants(),
+      [Command::Var1, Command::Var2, Command::Var3]
+    )
+  }
+
+  #[test]
+  fn text_representations() {
+    assert_eq!(Command::Var1.as_ref(), "var1");
+    assert_eq!(Command::Var2.as_ref(), "2");
+    assert_eq!(Command::Var3.as_ref(), "crazy");
+  }
+}