From 737bf192f4b74104b7e8f78ed9732e70aa44a5da Mon Sep 17 00:00:00 2001
From: Fabian Kirchner <kirchner@posteo.de>
Date: Mon, 2 Oct 2023 15:03:09 +0200
Subject: add command line argument parsing

---
 anissue.cabal |  3 ++-
 app/Main.hs   | 37 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/anissue.cabal b/anissue.cabal
index c9cf518..39aed05 100644
--- a/anissue.cabal
+++ b/anissue.cabal
@@ -71,7 +71,8 @@ executable anissue
     -- other-extensions:
 
     -- Other library packages from which modules are imported.
-    build-depends:    base ^>=4.16.4.0
+    build-depends:    base ^>=4.16.4.0,
+                      optparse-applicative
 
     -- Directories containing source files.
     hs-source-dirs:   app
diff --git a/app/Main.hs b/app/Main.hs
index 65ae4a0..e3c1a28 100644
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -1,4 +1,39 @@
 module Main where
 
+import Options.Applicative ((<**>))
+import Options.Applicative qualified as O
+
+data Options = Options
+  { optCommand :: Command
+  }
+  deriving (Show)
+
+data Command
+  = List
+  | Show
+  deriving (Show)
+
+optionsParser :: O.Parser Options
+optionsParser =
+  Options
+    <$> commandParser
+
+commandParser :: O.Parser Command
+commandParser =
+  O.subparser
+    ( O.command "list" (O.info listCommandParser (O.progDesc "List all issues"))
+        <> O.command "show" (O.info showCommandParser (O.progDesc "Show details of all issues"))
+    )
+
+listCommandParser :: O.Parser Command
+listCommandParser =
+  pure List
+
+showCommandParser :: O.Parser Command
+showCommandParser =
+  pure Show
+
 main :: IO ()
-main = putStrLn "Hello, Haskell!"
+main = do
+  options <- O.execParser (O.info (commandParser <**> O.helper) O.idm)
+  print options
-- 
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