refactor: Make commands know about their keywords

Now commands know about their own keywords and now only the Command
class, preventing wrong assumptions of responsability and coupled code.

src/bojack/command.cr

@@ -6,24 +6,26 @@ require "./commands/size"
 
 module Bojack
   module Command
+    REGISTRY = [
+      Bojack::Commands::Get,
+      Bojack::Commands::Set,
+      Bojack::Commands::Delete,
+      Bojack::Commands::Size,
+    ]
+
     # Factory method for Bojack Commands
     #
     # It holds the logic to create the command instances
     #
-    # @param param_command [String]
-    def self.from(param_command) : Bojack::Commands::Command?
-      case param_command
-      when "set"
-        Bojack::Commands::Set.new
-      when "get"
-        Bojack::Commands::Get.new
-      when "delete"
-        Bojack::Commands::Delete.new
-      when "size"
-        Bojack::Commands::Size.new
-      else
-        nil
+    # @param command [String]
+    def self.from(keyword) : Bojack::Commands::Command?
+      clazz = REGISTRY.find(nil) do |clazz|
+        clazz.keyword == keyword
       end
+
+      return clazz.new if clazz
+
+      nil
     end
   end
 end

src/bojack/commands/command.cr

@@ -5,6 +5,8 @@ module Bojack
     # Represents a Bojack command
     #
     abstract class Command
+      @@keyword : String = "none"
+
       # Execute method
       #
       # Implements the process for command.
@@ -13,6 +15,14 @@ module Bojack
       # @param key [String] for memory retrieve.
       # @param value [String] for memory changes.
       abstract def execute(memory, key : String?, value : String?) : String
+
+      private def self.keyword=(value : String)
+        @@keyword = value
+      end
+
+      def self.keyword
+        @@keyword
+      end
     end
   end
 end

src/bojack/commands/delete.cr

@@ -3,6 +3,8 @@ require "./command"
 module Bojack
   module Commands
     class Delete < Command
+      self.keyword = "delete"
+
       def execute(memory, key : String?, value : String?) : String
         memory.delete(key)
       rescue

src/bojack/commands/get.cr

@@ -3,6 +3,8 @@ require "./command"
 module Bojack
   module Commands
     class Get < Command
+      self.keyword = "get"
+
       def execute(memory, key : String?, value : String?) : String
         memory.read(key)
       rescue

src/bojack/commands/set.cr

@@ -3,6 +3,8 @@ require "./command"
 module Bojack
   module Commands
     class Set < Command
+      self.keyword = "set"
+
       def execute(memory, key : String?, value : String?) : String
         memory.write(key, value)
       end

src/bojack/commands/size.cr

@@ -3,6 +3,8 @@ require "./command"
 module Bojack
   module Commands
     class Size < Command
+      self.keyword = "size"
+
       def execute(memory, key : String?, value : String?) : String
         "#{memory.size}"
       end