Add prepend to ast method

Author: tomeroth

lib/filterly/node_builder.rb

@@ -15,6 +15,28 @@ def self.build_equality_node(attr_name:, attr_value:)
       )
     end
 
+    def self.build_not_equality_node(attr_name:, attr_value:)
+      Filterly::Node.new(
+        :expression,
+        [
+          :op_not_equal,
+          Filterly::Node.new(:attr_name, [attr_name, nil, nil]),
+          Filterly::Node.new(:attr_value, [attr_value, nil, nil])
+        ]
+      )
+    end
+
+    def self.build_exists_node(attr_name:, attr_value:)
+      Filterly::Node.new(
+        :expression,
+        [
+          :op_exists,
+          Filterly::Node.new(:attr_name, [attr_name, nil, nil]),
+          Filterly::Node.new(:attr_value, [attr_value, nil, nil])
+        ]
+      )
+    end
+
     def self.build_array_values_node(attr_name:, array_of_values:)
       Filterly::Node.new(
         :expression,

lib/filterly/tree.rb

@@ -10,31 +10,20 @@ def initialize(ast_node)
       @ast_node = ast_node
     end
 
+    def self.new(ast_node)
+      ensure_ast_node!(ast_node)
+
+      super(ast_node)
+    end
+
     def extend_ast(node_attr_name, new_node, stmt_type)
-      return if ast_node.nil?
-      if ast_node.attr_name_equal?(node_attr_name)
-        create_node(
-          :statement,
-          [
-            stmt_type,
-            new_node,
-            ast_node
-          ]
-        )
-      else
-        recreate_node(node_attr_name, new_node, stmt_type)
-      end
+      TreeTraverser.new(ast_node).extend_ast(node_attr_name, new_node, stmt_type)
     end
 
-    def recreate_node(node_attr_name, new_node, stmt_type)
-      create_node(
-        ast_node.type,
-        [
-          ast_node.value,
-          self.class.new(ast_node.left).extend_ast(node_attr_name, new_node, stmt_type),
-          self.class.new(ast_node.right).extend_ast(node_attr_name, new_node, stmt_type)
-        ]
-      )
+    def prepend_ast(new_node, stmt_type)
+      ensure_ast_root!
+
+      TreeTraverser.new(ast_node).prepend_ast(new_node, stmt_type)
     end
 
     def to_ast
@@ -45,9 +34,72 @@ def to_s
       ast_node.to_s
     end
 
+    # @apir private
+    def ensure_ast_root!
+      raise 'Not a tree root!' if ast_node.type != :root
+    end
+
     # @api private
-    def create_node(*args)
-      Filterly::Node.new(*args)
+    def self.ensure_ast_node!(ast_node)
+      raise 'Not a Filterfly:Node!' if ast_node.nil? || !ast_node.is_a?(Filterly::Node)
+    end
+
+    class TreeTraverser
+      attr_reader :ast_node
+
+      def initialize(ast_node)
+        @ast_node = ast_node
+      end
+
+      def extend_ast(node_attr_name, new_node, stmt_type)
+        return if ast_node.nil?
+        if ast_node.attr_name_equal?(node_attr_name)
+          create_node(
+            :statement,
+            [
+              stmt_type,
+              new_node,
+              ast_node
+            ]
+          )
+        else
+          recreate_node(node_attr_name, new_node, stmt_type)
+        end
+      end
+
+      def recreate_node(node_attr_name, new_node, stmt_type)
+        create_node(
+          ast_node.type,
+          [
+            ast_node.value,
+            self.class
+              .new(ast_node.left)
+              .extend_ast(node_attr_name, new_node, stmt_type),
+            self.class
+              .new(ast_node.right)
+              .extend_ast(node_attr_name, new_node, stmt_type)
+          ]
+        )
+      end
+
+      def prepend_ast(new_node, stmt_type)
+        create_node(
+          ast_node.type,
+          [
+            ast_node.value,
+            create_node(
+              :statement,
+              [stmt_type, new_node, ast_node.left]
+            ),
+            nil
+          ]
+        )
+      end
+
+      # @api private
+      def create_node(*args)
+        Filterly::Node.new(*args)
+      end
     end
   end
 end

spec/unit/node_builder_spec.rb

@@ -39,6 +39,54 @@
     end
   end
 
+  describe '#self.build_not_equality_node' do
+    it 'returns requested ast node' do
+      result = subject.build_not_equality_node(attr_name: 'course_id', attr_value: 12)
+
+      expect(result.to_a).to match_array(
+        [
+          :expression,
+          [
+            :op_not_equal,
+            [
+              :attr_name,
+              [
+                'course_id',
+                [],
+                []
+              ]
+            ],
+            [
+              :attr_value,
+              [
+                12,
+                [],
+                []
+              ]
+            ]
+          ]
+        ]
+      )
+    end
+  end
+
+  describe '#self.build_exists_node' do
+    it 'returns requested ast node' do
+      result = subject.build_exists_node(attr_name: 'course_id', attr_value: 12)
+
+      expect(result.to_a).to match_array(
+        [
+          :expression,
+          [
+            :op_exists,
+            [:attr_name, ['course_id', [], []]],
+            [:attr_value, [12, [], []]]
+          ]
+        ]
+      )
+    end
+  end
+
   describe '#self.build_array_values_node' do
     it 'returns requested ast node' do
       result = subject.build_array_values_node(