module IndexShotgun
  module Analyzer
    require "index_shotgun/array_start_with"

    class << self
      using IndexShotgun::ArrayStartWith

      def check_indexes(table)
        indexes = table_indexes(table)

        response = []
        indexes.each do |source_index|
          indexes.each do |target_index|
            next if source_index.name == target_index.name

            if source_index.columns.start_with?(target_index.columns)
              if target_index.unique
                last_column = source_index.columns.last
                response << {
                  index:  source_index,
                  result: "#{source_index.name} has unnecessary column #{last_column} (#{target_index.name} is unique index!)",
                }
              else
                response << {
                  index:  target_index,
                  result: "#{target_index.name} is a left-prefix of #{source_index.name}",
                }
              end
            end
          end
        end

        response
      end

      # get indexes of table
      # @param table [String]
      # @see [ActiveRecord::ConnectionAdapters::TableDefinition#indexes]
      def table_indexes(table)
        ActiveRecord::Base.connection.indexes(table)
      end
    end
  end
end