initial cli library

flake.nix

@@ -9,5 +9,14 @@
     packages.${system} = {
       default = pkgs.callPackage ./package.nix {};
     };
+    devShells.${system} = {
+      default = pkgs.mkShell {
+        nativeBuildInputs = [
+          pkgs.elmPackages.elm-format
+          pkgs.elm2nix
+          pkgs.elmPackages.elm-json
+        ];
+      };
+    };
   };
 }

src/Cli.elm

@@ -0,0 +1,103 @@
+module Cli exposing (..)
+
+
+type alias Parameter =
+    { name : String
+    }
+
+
+type alias FilledParameter =
+    { name : String
+    , content : String
+    }
+
+
+type alias DirtyCommand =
+    Command
+
+
+type alias Command =
+    { name : String
+    , params : List Parameter
+    }
+
+
+type alias FilledCommand =
+    { name : String
+    , params : List FilledParameter
+    }
+
+
+type alias CommandErr =
+    { command : Maybe Command
+    , got : String
+    , argumentErr : Maybe ArgumentErr
+    }
+
+type ArgumentErr
+    = MissingArgs
+    | TooManyArgs
+
+
+parseInput : List Command -> String -> Result CommandErr FilledCommand
+parseInput commands input =
+    let
+        tokens =
+            List.map String.trim (String.split " " input)
+    in
+    case List.head tokens of
+        Just maybeCommand ->
+            case List.head (List.filter (isCommand maybeCommand) commands) of
+                Just command ->
+                    case applyArguments command.params tokens of
+                        Ok list ->
+                            Ok
+                                { name = command.name
+                                , params = list
+                                }
+                        Err err ->
+                            Err { command = Just command
+                                , got = input
+                                , argumentErr = Just err
+                                }
+
+
+                Nothing ->
+                    Err
+                        { command = Nothing
+                        , got = input
+                        , argumentErr = Nothing
+                        }
+        Nothing ->
+            Err
+                { command = Nothing
+                , got = input
+                , argumentErr = Nothing
+                }
+
+
+applyArguments : List Parameter -> List String -> Result ArgumentErr (List FilledParameter)
+applyArguments params inputs =
+    if List.length params > List.length inputs then
+        Err MissingArgs
+    else if List.length params < List.length inputs then
+        Err TooManyArgs
+    else
+        Ok (List.map2 applyParameter params inputs)
+
+
+
+applyParameter : Parameter -> String -> FilledParameter
+applyParameter param input =
+    { name = param.name
+    , content = input
+    }
+        
+
+isCommand : String -> Command -> Bool
+isCommand name command =
+    if name == command.name then
+        True
+
+    else
+        False

src/Commands.elm

@@ -0,0 +1,12 @@
+module Commands exposing (..)
+
+import Cli exposing (Command)
+
+
+greet : Command
+greet =
+    { name = "greet"
+    , params = [
+        { name = "name"
+    } ]
+    }

src/Main.elm

@@ -16,6 +16,9 @@ import Json.Encode as E
 import Task
 import Url
 
+import Cli
+import Commands exposing (greet)
+
 
 
 -- MAIN
@@ -558,7 +561,7 @@ runHello : CommandRunner
 runHello model args =
     case List.head args of
         Nothing ->
-            ( { model | content = model.content ++ [ text "\nHello World!"] }, Cmd.none )
+            ( { model | content = model.content ++ [ text "\nHello World!" ] }, Cmd.none )
 
         _ ->
             ( { model | content = model.content ++ wrongArgs HelloCommand 0 args }, Cmd.none )