class InsertQuery
  def initialize(model_class, column_names, returning = nil)
    @model_class = model_class
    @column_names = column_names
    @returning = returning

    @rows = []
    @executed = false
  end

  def insert(model_attributes)
    ensure_not_executed

    rows << prepare_model_attributes(model_attributes, Time.zone.now)
  end

  def prepare_model_attributes(model_attributes, now)
    column_names.map do |column_name|
      prepare_model_attribute(column_name, model_attributes, now)
    end
  end

  def prepare_model_attribute(column_name, model_attributes, now)
    column_name = column_name.to_sym
    if %i(created_at updated_at).include?(column_name)
      if model_attributes.include?(column_name)
        model_attributes[column_name]
      else
        now
      end
    else
      model_attributes.fetch(column_name, :default)
    end
  end

  def execute
    ensure_not_executed

    yield(self) if block_given?
    result = connection.execute(query).values unless rows.empty?
    self.executed = true
    result
  end

  def self.execute(*constructor_args, &block)
    new(*constructor_args).execute(&block)
  end

  private

    attr_reader :model_class, :column_names, :rows, :returning
    attr_accessor :executed

    delegate :connection, to: :model_class

    def ensure_not_executed
      fail("the query has been already executed") if executed
    end

    def query
      <<-SQL
        INSERT INTO
          #{model_class.table_name}
          (#{column_names.join(', ')})
          VALUES #{
          rows.map do |row|
            "(#{row.map { |datum| quote(datum) }.join(', ')})"
          end.join(', ')
          }
          #{returning_clause}
      SQL
    end

    def quote(datum)
      if datum == :default
        'default'
      else
        connection.quote(datum)
      end
    end

    def returning_clause
      %(RETURNING #{returning}) if returning
    end
end