add query generator and tests for query generator

text_to_sql_query.rb

@@ -0,0 +1,79 @@
+require './parser'
+
+class TextToSqlQuery
+  def initialize(text, fields, default_field, fields_mappings = {})
+    @text = text.to_s.strip
+    @fields = fields.map(&:to_sym)
+    @default_field = default_field.to_sym
+    @fields_mappings = fields_mappings.merge(@fields.reduce({}) do |mappings, field|
+      _table_name, field_name = field.to_s.split('.')
+      mappings[field_name.to_sym] = field
+      mappings
+    end)
+  end
+
+  def where_clause
+    @parser = Query.new
+    @parsed_tree = @parser.parse(@text)
+    generate_sql @parsed_tree
+  end
+
+  private
+
+  def generate_sql(tree)
+    @first_key = tree.keys.first
+    case @first_key
+    when :DEFAULT_COLUMN
+      ["#{@default_field.to_s} LIKE ?", "%#{tree[@first_key]}%"]
+    when :OPERATOR_OR
+      generate_expression_for_logical_operator(:OR, tree[@first_key])
+    when :OPERATOR_AND
+      generate_expression_for_logical_operator(:AND, tree[@first_key])
+    when :OPERATOR_NOT
+      @not_array = generate_sql tree[@first_key]
+
+      if @not_array.length < 2
+        raise "There should be more than 1 element for expression following NOT operator"
+      end
+
+      @not_expression = @not_array.first
+      @not_params = @not_array[1..]
+
+      ["NOT #{@not_expression}"] + @not_params
+
+    else
+      # key is column name
+      @mapping = @fields_mappings[@first_key.to_sym]
+      if @mapping.nil?
+        ["#{@default_field.to_s} LIKE ?", "%#{tree[@first_key]}%"]
+      else
+        ["#{@mapping.to_s} LIKE ?", "%#{tree[@first_key]}%"]
+      end
+    end
+  end
+
+  def generate_expression_for_logical_operator(operator, operator_array)
+    if operator_array.length != 2
+      raise "There should be two array elements for #{operator.to_s} operator"
+    end
+
+    @first_operand = generate_sql operator_array.first
+    @second_operand = generate_sql operator_array.last
+
+    if @first_operand.length < 2
+      raise 'There should be more than 1 element in first operand array'
+    end
+
+    if @second_operand.length < 2
+      raise 'There should be more than 1 element in second operand array'
+    end
+
+    @first_operand_expression = @first_operand.first
+    @first_operand_params = @first_operand[1..]
+
+    @second_operand_expression = @second_operand.first
+    @second_operand_params = @second_operand[1..]
+
+    ["#{@first_operand_expression} #{operator.to_s} #{@second_operand_expression}"] + @first_operand_params + @second_operand_params
+  end
+end