amend-line: refactor + overengineer the f*ck out of it, for the lulz

lib/pry/commands/amend_line.rb

@@ -16,32 +16,82 @@ class Pry
     BANNER
 
     def process
-      start_line_number, end_line_number, replacement_line = *args
+      raise CommandError, "No input to amend." if eval_string.empty?
 
-      if eval_string.empty?
-        raise CommandError, "No input to amend."
-      end
+      eval_string.replace amended_input(eval_string)
+      run "show-input"
+    end
 
-      replacement_line = "" if !replacement_line
+    private
+
+    # @param [String] string The string to amend.
+    # @return [String] A new string with the amendments applied to it.
+    def amended_input(string)
       input_array = eval_string.each_line.to_a
 
-      end_line_number = start_line_number.to_i if !end_line_number
-      line_range = start_line_number ? (one_index_number(start_line_number.to_i)..one_index_number(end_line_number.to_i))  : input_array.size - 1
-
-      # delete selected lines if replacement line is '!'
       if arg_string == "!"
-        input_array.slice!(line_range)
+        delete_from_array(input_array, line_range)
       elsif arg_string.start_with?(">")
-        insert_slot = Array(line_range).first
-        input_array.insert(insert_slot, arg_string[1..-1] + "\n")
+        insert_into_array(input_array, line_range)
       else
-        input_array[line_range] = arg_string + "\n"
+        replace_in_array(input_array, line_range)
+      end
+
+      input_array.join
+    end
+
+    def delete_from_array(array, range)
+      array.slice!(range)
+    end
+
+    def insert_into_array(array, range)
+      insert_slot = Array(range).first
+      array.insert(insert_slot, arg_string[1..-1] + "\n")
+    end
+
+    def replace_in_array(array, range)
+      array[range] = arg_string + "\n"
+    end
+
+    # @return [Fixnum] The number of lines currently in `eval_string` (the input buffer).
+    def line_count
+      eval_string.lines.count
+    end
+
+    # Returns the (one-indexed) start and end lines given by the user.
+    # The lines in this range will be affected by the `amend-line`.
+    # Returns `nil` if no lines were specified by the user.
+    # @return [Array<Fixnum>, nil]
+    def start_and_end_line_number
+      start_line_number, end_line_number = args
+      end_line_number ||= start_line_number.to_i
+
+      [start_line_number.to_i, end_line_number.to_i] if start_line_number
+    end
+
+    # Takes two numbers that are 1-indexed, and returns a range (or
+    # number) that is 0-indexed. 1-indexed means the first element is
+    # indentified by 1 rather than by 0 (as is the case for Ruby arrays).
+    # @param [Fixnum] start_line_number One-indexed number.
+    # @param [Fixnum] end_line_number One-indexed number.
+    # @return [Range] The zero-indexed range.
+    def zero_indexed_range_from_one_indexed_numbers(start_line_number, end_line_number)
+      # FIXME: one_index_number is a horrible name for this method
+      one_index_number(start_line_number)..one_index_number(end_line_number)
+    end
+
+    # The lines (or line) that will be modified by the `amend-line`.
+    # @return [Range, Fixnum] The lines or line.
+    def line_range
+      start_line_number, end_line_number = start_and_end_line_number
+      if start_line_number
+        zero_indexed_range_from_one_indexed_numbers(start_line_number,
+                                                    end_line_number)
+      else
+        line_count - 1
       end
-      eval_string.replace input_array.join
-      run "show-input"
     end
   end
 
   Pry::Commands.add_command(Pry::Command::AmendLine)
 end
-