add bash completion

flake.nix

@@ -17,6 +17,7 @@
               src = self;
               installPhase = ''
                 install -m 755 -D gra $out/bin/gra
+                install -m 644 -D gra_completion.bash $out/share/bash-completion/completions/gra
               '';
             };
             default = self.packages.${system}.gra;

gra_completion.bash

@@ -0,0 +1,16 @@
+function _gra_completion {
+
+    _args="-h --help"
+
+    # Add config values to completion
+    if [ "${#COMP_WORDS[@]}" -lt 3 ] && [ -f ~/.config/gra.config ]; then
+        readarray -t lines < ~/.config/gra.config
+        for line in "${lines[@]}"; do
+            [[ "$line" =~ ^(.*)= ]] && _args="$_args ${BASH_REMATCH[1]}"
+        done
+    fi
+
+    COMPREPLY=($(compgen -W "$_args" -- "${COMP_WORDS[COMP_CWORD]}"))
+}
+
+complete -F _gra_completion gra