require 'json'
require 'flydata-core/postgresql/snapshot'

module FlydataCore
module Postgresql

class SourcePos
  include Comparable

  # Source Position data for PostgreSQL
  #
  # Format:
  #   <from-snaphost><TAB><to-snapshot><TAB><pk-values(JSON)>
  #
  #   from-snapshot: Store txid_snapshot guaranteeing the changes up to this snapshot are sent
  #   pk_values: Store primary key values of the last record on the last request/transaction
  #
  #
  # ex1: No resume position
  #
  #   1031:1031:<TAB>
  #
  #   -> Changes up to 1031:1031: were sent.
  #      Agent will fetch the change between the latest snapshot and 1031:1031:
  #
  # ex2: Resume position with single primary key
  #
  #   1031:1031:<TAB>1032:1032:<TAB>[{"id":10000}]
  #
  #   -> Changes up to 1031:1031: and partial changes (id <= 10000) between 1032:1032: and 1031:1031: were sent.
  #      Agent will fetch the change between 1032:1032: and 1031:1031: with a primary key condisions(id > 10000)
  #
  # ex3: Resume position with multiple primary keys
  #
  #   1031:1031:<TAB>1033:1033:<TAB>[{"group":"apple"},{"name":"TOM"}]
  #
  #   -> Changes up to 1031:1031: and partial changes (group<='apple' and name<='TOM') between 1033:1033: and 1031:1031: were sent.
  #      Agent will fetch the change between 1033:1033: and 1031:1031: with a primary key condisions(group >= 'apple' and name >= 'TOM')
  #
  def initialize(snapshot_or_obj, to_snapshot = nil, pk_values = nil)
    if snapshot_or_obj.kind_of?(self.class)
      snapshot_or_obj.tap do |s|
        @snapshot = s.snapshot
        @to_snapshot = s.to_snapshot
        @pk_values = s.pk_values
      end
    else
      @snapshot = Snapshot.new(snapshot_or_obj)
      @to_snapshot = if to_snapshot.to_s.empty?
                       nil
                     else
                       Snapshot.new(to_snapshot)
                     end
      @pk_values = pk_values  # must be array or nil
    end
  end

  attr_reader :snapshot
  attr_reader :to_snapshot
  attr_reader :pk_values

  def empty?
    @snapshot.empty?
  end

  def to_s
    pk_values = @pk_values ? @pk_values.to_json : ''
    "#{@snapshot}\t#{@to_snapshot}\t#{pk_values}"
  end

  #TODO: Need to revisit the logic along with the spec
  #  http://www.postgresql.org/docs/9.5/static/functions-info.html#FUNCTIONS-TXID-SNAPSHOT-PARTS
  def <=>(other)
    if @snapshot != other.snapshot
      return @snapshot <=> other.snapshot
    elsif @pk_values.nil? && !other.pk_values.nil?
      1
    elsif !@pk_values.nil? && other.pk_values.nil?
      -1
    elsif @pk_values == other.pk_values
      0
    else
      @pk_values.to_s <=> other.pk_values.to_s
    end
  end

  def self.load(str)
    snapshot, to_snapshot, pk_values = str.split("\t").collect{|v| v.strip}
    pk_values = if pk_values.to_s.empty?
                  nil
                else
                  JSON.parse(pk_values)
                end
    self.new(snapshot, to_snapshot, pk_values)
  end
end

end
end