module ActiveRecord
  module Associations
    class Preloader
      class Association #:nodoc:
        attr_reader :owners, :reflection, :preload_scope, :model, :klass
        attr_reader :preloaded_records

        def initialize(klass, owners, reflection, preload_scope)
          @klass         = klass
          @owners        = owners
          @reflection    = reflection
          @preload_scope = preload_scope
          @model         = owners.first && owners.first.class
          @scope         = nil
          @preloaded_records = []
        end

        def run(preloader)
          preload(preloader)
        end

        def preload(preloader)
          raise NotImplementedError
        end

        def scope
          @scope ||= build_scope
        end

        def records_for(ids)
          query_scope(ids)
        end

        def query_scope(ids)
          scope.where(association_key_name => ids)
        end

        def table
          klass.arel_table
        end

        # The name of the key on the associated records
        def association_key_name
          raise NotImplementedError
        end

        # This is overridden by HABTM as the condition should be on the foreign_key column in
        # the join table
        def association_key
          table[association_key_name]
        end

        # The name of the key on the model which declares the association
        def owner_key_name
          raise NotImplementedError
        end

        def options
          reflection.options
        end

        private

        def associated_records_by_owner(preloader)
          records = load_records
          owners.each_with_object({}) do |owner, result|
            result[owner] = records[convert_key(owner[owner_key_name])] || []
          end
        end

        def owner_keys
          unless defined?(@owner_keys)
            @owner_keys = owners.map do |owner|
              owner[owner_key_name]
            end
            @owner_keys.uniq!
            @owner_keys.compact!
          end
          @owner_keys
        end

        def key_conversion_required?
          @key_conversion_required ||= association_key_type != owner_key_type
        end

        def convert_key(key)
          if key_conversion_required?
            key.to_s
          else
            key
          end
        end

        def association_key_type
          @klass.type_for_attribute(association_key_name.to_s).type
        end

        def owner_key_type
          @model.type_for_attribute(owner_key_name.to_s).type
        end

        def load_records
          return {} if owner_keys.empty?
          # Some databases impose a limit on the number of ids in a list (in Oracle it's 1000)
          # Make several smaller queries if necessary or make one query if the adapter supports it
          slices  = owner_keys.each_slice(klass.connection.in_clause_length || owner_keys.size)
          @preloaded_records = slices.flat_map do |slice|
            records_for(slice)
          end
          @preloaded_records.group_by do |record| 
            convert_key(record[association_key_name])
          end
        end

        def reflection_scope
          @reflection_scope ||= reflection.scope ? klass.unscoped.instance_exec(nil, &reflection.scope) : klass.unscoped
        end

        def build_scope
          scope = klass.unscoped

          values = reflection_scope.values
          preload_values = preload_scope.values

          scope.where_clause = reflection_scope.where_clause + preload_scope.where_clause
          scope.references_values = Array(values[:references]) + Array(preload_values[:references])

          if preload_values[:select] || values[:select]
            scope._select!(preload_values[:select] || values[:select])
          end
          scope.includes! preload_values[:includes] || values[:includes]
          if preload_scope.joins_values.any?
            scope.joins!(preload_scope.joins_values)
          else
            scope.joins!(reflection_scope.joins_values)
          end

          if order_values = preload_values[:order] || values[:order]
            scope.order!(order_values)
          end

          if preload_values[:reordering] || values[:reordering]
            scope.reordering_value = true
          end

          if preload_values[:readonly] || values[:readonly]
            scope.readonly!
          end

          if options[:as]
            scope.where!(klass.table_name => { reflection.type => model.base_class.sti_name })
          end

          scope.unscope_values = Array(values[:unscope]) + Array(preload_values[:unscope])
          klass.default_scoped.merge(scope)
        end
      end
    end
  end
end
