module PgGraph::Data
  class Association
    attr_reader :this_table
    attr_reader :this_field
    attr_reader :that_table
    attr_reader :that_field

    # Dimension of the association
    attr_reader :dimension

    def initialize(dimension, this_table, that_table, this_field, that_field)
      Dimension.validate(dimension, min: 1)
      constrain this_table, Table
      constrain that_table, Table
      constrain this_field, String, Symbol
      constrain that_field, String, Symbol
      @dimension = dimension
      @this_table, @this_field = this_table, this_field
      @that_table, @that_field = that_table, that_field
    end

    # Query the association and return a query object (Record, Query, or
    # QueryWithDuplicates)
    def query(field) raise NotThis end

    # Get object(s). Either a single record or a list of (possible duplicate)
    # records
    def get(record) dimension == 1 ? get_record(record) : get_records(record) end

    def get_record(this_record)
      if that_field == :id
        that_table[this_record[this_field].value]
      else
        that_table.records.find { |that_record|
          that_record[that_field].value == this_record[this_field].value
        }
      end
    end

    def get_records(this_record)
      that_table.records.find_all { |that_record|
        that_record[that_field].value == this_record[this_field].value
      }
    end
  end

  class KindAssociation < Association
  end

  class LinkAssociation < Association
    # From this table to the link table. TableAssociation object
    attr_reader :this_association

    # From the link table to 'that' table. RecordAssociation object
    attr_reader :that_association 

    # The link table in the N:M relation
    def link_table() this_association.that_table end

    # The field in the link table that links to this record
    def this_link_field() this_association.that_field end

    # The field in the link table that links to that record
    def that_link_field() that_association.this_field end

    def initialize(
        dimension,
        this_table, that_table, link_table, 
        this_field, this_link_field, that_link_field, that_field)
      super(dimension, this_table, that_table, this_field, that_field)
      @this_association = Association.new(2, this_table, link_table, this_field, this_link_field)
      @that_association = Association.new(1, link_table, that_table, that_link_field, that_field)
    end

    # Note that records are not unique for MmTableAssociation but for
    # NmTableAssociation objects
    def get_records(record)
      @this_association.get(record).map { |link_record| @that_association.get(link_record) }
    end
  end
end