fix shfmt formatter and add support for custom command

Author: DannyBen

lib/bashly/libraries/settings/settings.yml

@@ -52,11 +52,12 @@ strict: false
 tab_indent: false
 
 # Choose a post-processor for the generated script:
-# formatter: internal   # Use Bashly's internal formatter (compacts newlines)
-# formatter: none       # Disable all post-processing
-# formatter: shfmt      # Use shfmt if installed
-formatter: internal
-
+# formatter: :internal   # Use Bashly's internal formatter (compacts newlines)
+# formatter: :none       # Disable all post-processing
+# formatter: :shfmt      # Use shfmt if installed
+# formatter: shfmt -mn   # Use any other string, assuming the command accepts
+#                        # the script as stdin and outputs it to stdout
+formatter: :internal
 
 #-------------------------------------------------------------------------------
 # INTERFACE OPTIONS

lib/bashly/script/formatter.rb

@@ -1,4 +1,5 @@
 require 'open3'
+require 'shellwords'
 
 module Bashly
   module Script
@@ -9,29 +10,28 @@ class Formatter
 
       def initialize(script, mode: nil)
         @script = script
-        @mode = MODES.include?(mode&.to_sym) ? mode.to_sym : MODES.first
+        @mode = mode
       end
 
       def formatted_script
         case mode
         when :internal then script.gsub(/\s+\n/m, "\n\n")
         when :shfmt then shfmt_result
-        else script
+        when :none then script
+        else custom_formatter_result mode
         end
       end
 
     private
 
       def shfmt_result
-        unless system 'command -v shfmt > /dev/null 2>&1'
-          raise DependencyError,
-            'Cannot find g`shfmt`.\nEither install it or change to the g`internal` formatter.'
-        end
-
-        output, error, status =
-          Open3.capture3 %w[shfmt --case-indent --indent 2], stdin_data: script
+        custom_formatter_result %w[shfmt --case-indent --indent 2]
+      end
 
-        raise DependencyError, "Failed running g`shfmt`:\n\n#{error}" unless status.success?
+      def custom_formatter_result(command)
+        command = Shellwords.split command if command.is_a? String
+        output, error, status = Open3.capture3 *command, stdin_data: script
+        raise DependencyError, "Failed running g`#{command}`:\n\n#{error}" unless status.success?
 
         output
       end