require "pg_meta"

# Extend MetaDb with a link table detection method
module PgMeta
  class Table
    # True if table is a N:M link table. A N:M relation allows for multiple
    # relations between two records
    #
    # A table is a N:M table if
    #   o it has a primary key named 'id' as the first column
    #   o has two reference fields using the link field naming convention
    #   o and nothing else
    #
    def mm_table?
      @mm_table ||= 
          if columns.size != 3
            false
          elsif columns.values.first.name != "id" || columns.values.first != primary_key_column
            false
          else
            referential_constraints.size == 2 &&
            referential_constraints.values.map { |constraint|
              constraint.referencing_columns
            }.sort == [[columns.values[1]], [columns.values[2]]].sort
          end
    end

    # True if table is a N:N link table. A N:N relation have at most one
    # relation between two records. A N:N link table is also a M:M table
    #
    # A table is a N:N link table if
    #   o it has a primary key named 'id' as the first column
    #   o has two reference fields using the link field naming convention
    #   o has a unique index on the two reference fields
    #   o and nothing else
    #
    def nm_table?
      @nm_table ||= @mm_table && begin
        expected_columns = referential_constraints.values.map(&:columns).flatten.sort
        unique_constraints.values.any? { |constraint|
          expected_columns == constraint.columns.sort
        }
      end
    end

    def path
      schema.name + "." + name
    end
  end

  class Column
    def path() table.path + "." + name end
  end
end