1 files changed, 158 insertions, 0 deletions
diff --git a/src/arg_util.rs b/src/arg_util.rs
new file mode 100644
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+++ b/src/arg_util.rs
@@ -0,0 +1,158 @@
+// arg_util.rs
+
+// *************************************************************************
+// * Copyright (C) 2019 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),*)
+  }
+}
+
+/// 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 {
+  ( $name:ident, [ $( $var:ident => ($str:expr, $exec:expr), ) *] ) => {
+    Enum! {$name, [
+      $( $var => $str, )*
+    ]}
+
+    #[allow(unused_qualifications)]
+    impl $name {
+      fn execute(
+        self,
+        ctx: &mut crate::args::ExecCtx<'_>,
+        args: ::std::vec::Vec<::std::string::String>,
+      ) -> crate::Result<()> {
+        match self {
+          $(
+            $name::$var => $exec(ctx, args),
+          )*
+        }
+      }
+    }
+  };
+  ( $name:ident, [ $( $var:ident => $str:expr, ) *] ) => {
+    #[derive(Clone, Copy, Debug, PartialEq)]
+    pub enum $name {
+      $(
+        $var,
+      )*
+    }
+
+    impl $name {
+      #[allow(unused)]
+      pub fn all(&self) -> [$name; count!($($var),*) ] {
+        $name::all_variants()
+      }
+
+      pub fn all_variants() -> [$name; count!($($var),*) ] {
+        [
+          $(
+            $name::$var,
+          )*
+        ]
+      }
+    }
+
+    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 = ();
+
+      fn from_str(s: &str) -> ::std::result::Result<Self, Self::Err> {
+        match s {
+          $(
+            $str => Ok($name::$var),
+          )*
+          _ => Err(()),
+        }
+      }
+    }
+  };
+}
+
+/// A macro for formatting the variants of an enum (as created by the
+/// Enum!{} macro) ready to be used in a help text. The supplied `fmt`
+/// needs to contain the named parameter `{variants}`, which will be
+/// replaced with a generated version of the enum's variants.
+macro_rules! fmt_enum {
+  ( $enm:ident ) => {{
+    fmt_enum!($enm.all())
+  }};
+  ( $all:expr ) => {{
+    $all
+      .iter()
+      .map(::std::convert::AsRef::as_ref)
+      .collect::<::std::vec::Vec<_>>()
+      .join("|")
+  }};
+}
+
+/// A macro for generating the help text for a command/subcommand. The
+/// argument is the variable representing the command (which in turn is
+/// an enum).
+/// Note that the name of this variable is embedded into the help text!
+macro_rules! cmd_help {
+  ( $cmd:ident ) => {
+    format!(
+      concat!("The ", stringify!($cmd), " to execute ({})"),
+      fmt_enum!($cmd)
+    )
+  };
+}
+
+#[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");
+  }
+}