# encoding: utf-8

module Veritas
  module SQL
    module Generator

      # Generates an SQL statement for a literal
      module Literal

        TRUE            = 'TRUE'.freeze
        FALSE           = 'FALSE'.freeze
        NULL            = 'NULL'.freeze
        QUOTE           = "'".freeze
        ESCAPED_QUOTE   = "''".freeze
        SEPARATOR       = ', '.freeze
        DATE_FORMAT     = '%F'.freeze
        DATETIME_FORMAT = "#{DATE_FORMAT}T%T.%N%Z".freeze
        TIME_SCALE      = 9

        # Returns an unfrozen object
        #
        # Some objects, like Date, DateTime and Time memoize values
        # when serialized to a String, so when they are frozen this will
        # dup them and then return the unfrozen copy.
        #
        # @param [Object] object
        #
        # @return [Object]
        #   non-frozen object
        #
        # @api private
        def self.dup_frozen(object)
          object.frozen? ? object.dup : object
        end

        # Visit an Enumerable
        #
        # @param [Enumerable] enumerable
        #
        # @return [#to_s]
        #
        # @api private
        def visit_enumerable(enumerable)
          "(#{enumerable.map { |entry| dispatch entry }.join(SEPARATOR)})"
        end

        # Visit a String
        #
        # @note The string must be utf-8 encoded
        #
        # @param [String] string
        #
        # @return [#to_s]
        #
        # @api private
        def visit_string(string)
          "#{QUOTE}#{string.gsub(QUOTE, ESCAPED_QUOTE)}#{QUOTE}"
        end

        # Visit a Numeric
        #
        # @param [Numeric] numeric
        #
        # @return [#to_s]
        #
        # @api private
        def visit_numeric(numeric)
          numeric.to_s
        end

        # Visit a Class
        #
        # @param [Class] klass
        #
        # @return [#to_s]
        #
        # @api private
        def visit_class(klass)
          name = klass.name.to_s
          name.empty? ? NULL : visit_string(name)
        end

        # Visit a Date and return in ISO 8601 date format
        #
        # @param [Date] date
        #
        # @return [#to_s]
        #
        # @todo use Date#iso8601 when added to 1.8.7 by backports
        #
        # @api private
        def visit_date(date)
          dispatch Literal.dup_frozen(date).strftime(DATE_FORMAT)
        end

        # Visit a DateTime and return in ISO 8601 date-time format
        #
        # Converts the DateTime to UTC format.
        #
        # @param [DateTime] date_time
        #
        # @return [#to_s]
        #
        # @todo use DateTime#iso8601(TIME_SCALE) when added to 1.8.7 by backports
        #
        # @api private
        def visit_date_time(date_time)
          dispatch date_time.new_offset.strftime(DATETIME_FORMAT)
        end

        # Visit a Time
        #
        # Converts the Time to UTC format.
        #
        # @param [Time] time
        #
        # @return [#to_s]
        #
        # @api private
        def visit_time(time)
          dispatch Literal.dup_frozen(time).utc.iso8601(TIME_SCALE)
        end

        # Visit a true value
        #
        # @param [true]
        #
        # @return [#to_s]
        #
        # @api private
        def visit_true_class(_true)
          TRUE
        end

        # Visit a false value
        #
        # @param [false]
        #
        # @return [#to_s]
        #
        # @api private
        def visit_false_class(_false)
          FALSE
        end

        # Visit a nil value
        #
        # @param [nil]
        #
        # @return [#to_s]
        #
        # @api private
        def visit_nil_class(_nil)
          NULL
        end

      end # module Literal
    end # module Generator
  end # module SQL
end # module Veritas