class Upsert
  class Buffer
    class PG_Connection < Buffer
      # @private
      # activerecord-3.2.5/lib/active_record/connection_adapters/postgresql_adapter.rb#column_definitions
      class ColumnDefinition
        class << self
          def auto_increment_primary_key(connection, table_name)
            res = connection.exec <<-EOS
              SELECT attr.attname, seq.relname
              FROM pg_class      seq,
                   pg_attribute  attr,
                   pg_depend     dep,
                   pg_namespace  name,
                   pg_constraint cons
              WHERE seq.oid           = dep.objid
                AND seq.relkind       = 'S'
                AND attr.attrelid     = dep.refobjid
                AND attr.attnum       = dep.refobjsubid
                AND attr.attrelid     = cons.conrelid
                AND attr.attnum       = cons.conkey[1]
                AND cons.contype      = 'p'
                AND dep.refobjid      = '#{connection.quote_ident(table_name.to_s)}'::regclass
EOS
            if hit = res.first
              hit['attname']
            end
          end

          def all(connection, table_name)
            auto_increment_primary_key = auto_increment_primary_key(connection, table_name)
            res = connection.exec <<-EOS
SELECT a.attname AS name, format_type(a.atttypid, a.atttypmod) AS sql_type, d.adsrc AS default
  FROM pg_attribute a LEFT JOIN pg_attrdef d
    ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '#{connection.quote_ident(table_name.to_s)}'::regclass
   AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum
 EOS
            res.reject do |row|
              row['name'] == auto_increment_primary_key
            end.map do |row|
              new row['name'], row['sql_type'], row['default']
            end
          end
        end

        attr_reader :name
        attr_reader :sql_type
        attr_reader :default
        
        def initialize(name, sql_type, default)
          @name = name
          @sql_type = sql_type
          @default = default
        end
      end
    end
  end
end