require "set"

module ActiveRecord
  module ConnectionAdapters
    # A module for mapping CipherStash internal columns to columns that ActiveRecord can work with.
    #
    # @private
    class CipherStashColumnMapper
      ENCRYPTED_INDEX_COLUMN_REGEX = /^__.+_(match|ore|unique)$/
      ENCRYPTED_SOURCE_COLUMN_REGEX = /^__(.+)_encrypted$/

      class << self
        # Maps the given column definitions by filtering out CipherStash internal columns. This method
        # also adds in plaintext columns if necessary (for example, when using the driver in "encrypted"
        # mode after the original plaintext columns have been dropped).
        def map_column_definitions(column_definitions)
          all_column_names = column_definitions.map(&:first).to_set

          column_definitions
            .reject { |column_definition| encrypted_index_column?(column_definition) }
            .map { |column_definition| maybe_rename_source_column(column_definition, all_column_names) }
            .reject { |column_definition| encrypted_source_column?(column_definition) }
        end

        private

          def encrypted_index_column?(column_definition)
            ENCRYPTED_INDEX_COLUMN_REGEX =~ column_name(column_definition)
          end

          def encrypted_source_column?(column_definition)
            ENCRYPTED_SOURCE_COLUMN_REGEX =~ column_name(column_definition)
          end

          def column_name(column_definition)
            column_definition.first
          end

          def maybe_rename_source_column(column_definition, all_column_names)
            column_name, *rest = column_definition
            match = column_name.match(ENCRYPTED_SOURCE_COLUMN_REGEX)

            if match && !all_column_names.include?(match.captures.first)
              [match.captures.first, *rest]
            else
              column_definition
            end
          end
      end
    end
  end
end