require 'enumerator'

module ActiveRecord
  # = Active Record Through Association Scope
  module Associations
    module ThroughAssociationScope

      protected

      def construct_find_scope
        {
          :conditions => construct_conditions,
          :joins      => construct_joins,
          :include    => @reflection.options[:include] || @reflection.source_reflection.options[:include],
          :select     => construct_select,
          :order      => @reflection.options[:order],
          :limit      => @reflection.options[:limit],
          :readonly   => @reflection.options[:readonly]
        }
      end
      
      def construct_create_scope
        @reflection.nested? ? {} : construct_owner_attributes(@reflection)
      end

      # Build SQL conditions from attributes, qualified by table name.
      def construct_conditions
        reflection = @reflection.through_reflection_chain.last
        
        if reflection.macro == :has_and_belongs_to_many
          table_alias = table_aliases[reflection].first
        else
          table_alias = table_aliases[reflection]
        end
        
        parts = construct_quoted_owner_attributes(reflection).map do |attr, value|
          "#{table_alias}.#{attr} = #{value}"
        end
        parts += reflection_conditions(0)
        
        "(" + parts.join(') AND (') + ")"
      end

      # Associate attributes pointing to owner, quoted.
      def construct_quoted_owner_attributes(reflection)
        if as = reflection.options[:as]
          { "#{as}_id" => owner_quoted_id(reflection),
            "#{as}_type" => reflection.klass.quote_value(
              @owner.class.base_class.name.to_s,
              reflection.klass.columns_hash["#{as}_type"]) }
        elsif reflection.macro == :belongs_to
          { reflection.klass.primary_key => @owner.class.quote_value(@owner[reflection.primary_key_name]) }
        else
          { reflection.primary_key_name => owner_quoted_id(reflection) }
        end
      end

      def construct_select(custom_select = nil)
        distinct = "DISTINCT " if @reflection.options[:uniq]
        selected = custom_select || @reflection.options[:select] || "#{distinct}#{@reflection.quoted_table_name}.*"
      end
      
      def construct_joins(custom_joins = nil)
        "#{construct_through_joins} #{@reflection.options[:joins]} #{custom_joins}"
      end

      def construct_through_joins
        joins, right_index = [], 1
        
        # Iterate over each pair in the through reflection chain, joining them together
        @reflection.through_reflection_chain.each_cons(2) do |left, right|
          right_table_and_alias = table_name_and_alias(right.quoted_table_name, table_aliases[right])
          
          if left.source_reflection.nil?
            case left.macro
              when :belongs_to
                joins << inner_join_sql(
                  right_table_and_alias,
                  table_aliases[left],  left.association_primary_key,
                  table_aliases[right], left.primary_key_name,
                  reflection_conditions(right_index)
                )
              when :has_many, :has_one
                joins << inner_join_sql(
                  right_table_and_alias,
                  table_aliases[left],  left.primary_key_name,
                  table_aliases[right], right.association_primary_key,
                  polymorphic_conditions(left, left),
                  reflection_conditions(right_index)
                )
              when :has_and_belongs_to_many
                joins << inner_join_sql(
                  right_table_and_alias,
                  table_aliases[left].first, left.primary_key_name,
                  table_aliases[right],      right.klass.primary_key,
                  reflection_conditions(right_index)
                )
            end
          else
            case left.source_reflection.macro
              when :belongs_to
                joins << inner_join_sql(
                  right_table_and_alias,
                  table_aliases[left],  left.association_primary_key,
                  table_aliases[right], left.primary_key_name,
                  source_type_conditions(left),
                  reflection_conditions(right_index)
                )
              when :has_many, :has_one
                if right.macro == :has_and_belongs_to_many
                  join_table, right_table = table_aliases[right]
                  right_table_and_alias   = table_name_and_alias(right.quoted_table_name, right_table)
                else
                  right_table = table_aliases[right]
                end
              
                joins << inner_join_sql(
                  right_table_and_alias,
                  table_aliases[left], left.primary_key_name,
                  right_table,         left.source_reflection.active_record_primary_key,
                  polymorphic_conditions(left, left.source_reflection),
                  reflection_conditions(right_index)
                )
                
                if right.macro == :has_and_belongs_to_many
                  joins << inner_join_sql(
                    table_name_and_alias(
                      quote_table_name(right.options[:join_table]),
                      join_table
                    ),
                    right_table, right.klass.primary_key,
                    join_table,  right.association_foreign_key
                  )
                end
              when :has_and_belongs_to_many
                join_table, left_table = table_aliases[left]
                
                joins << inner_join_sql(
                  table_name_and_alias(
                    quote_table_name(left.source_reflection.options[:join_table]),
                    join_table
                  ),
                  left_table, left.klass.primary_key,
                  join_table, left.association_foreign_key
                )
                
                joins << inner_join_sql(
                  right_table_and_alias,
                  join_table,           left.primary_key_name,
                  table_aliases[right], right.klass.primary_key,
                  reflection_conditions(right_index)
                )
            end
          end
          
          right_index += 1
        end
        
        joins.join(" ")
      end

      def alias_tracker
        @alias_tracker ||= AliasTracker.new
      end

      def table_aliases
        @table_aliases ||= begin
          @reflection.through_reflection_chain.inject({}) do |aliases, reflection|
            table_alias = quote_table_name(alias_tracker.aliased_name_for(
              reflection.table_name,
              table_alias_for(reflection, reflection != @reflection)
            ))
            
            if reflection.macro == :has_and_belongs_to_many ||
                 (reflection.source_reflection &&
                  reflection.source_reflection.macro == :has_and_belongs_to_many)
              
              join_table_alias = quote_table_name(alias_tracker.aliased_name_for(
                (reflection.source_reflection || reflection).options[:join_table],
                table_alias_for(reflection, true)
              ))
              
              aliases[reflection] = [join_table_alias, table_alias]
            else
              aliases[reflection] = table_alias
            end
            
            aliases
          end
        end
      end
      
      def table_alias_for(reflection, join = false)
        name = alias_tracker.pluralize(reflection.name)
        name << "_#{@reflection.name}"
        name << "_join" if join
        name
      end
      
      def quote_table_name(table_name)
        @reflection.klass.connection.quote_table_name(table_name)
      end
      
      def table_name_and_alias(table_name, table_alias)
        "#{table_name} #{table_alias if table_alias != table_name}".strip
      end
      
      def inner_join_sql(table, on_left_table, on_left_key, on_right_table, on_right_key, *conditions)
        conditions << "#{on_left_table}.#{on_left_key} = #{on_right_table}.#{on_right_key}"
        conditions = conditions.flatten.compact
        conditions = conditions.map { |sql| "(#{sql})" } * ' AND '
        
        "INNER JOIN #{table} ON #{conditions}"
      end
      
      def reflection_conditions(index)
        reflection            = @reflection.through_reflection_chain[index]
        reflection_conditions = @reflection.through_conditions[index]
        
        conditions = []
        
        if reflection.options[:as].nil? && # reflection.klass is a Module if :as is used
           reflection.klass.finder_needs_type_condition?
          conditions << reflection.klass.send(:type_condition).to_sql
        end
        
        reflection_conditions.each do |condition|
          sanitized_condition    = reflection.klass.send(:sanitize_sql, condition)
          interpolated_condition = interpolate_sql(sanitized_condition)
          
          if condition.is_a?(Hash)
            interpolated_condition.gsub!(
              @reflection.quoted_table_name,
              reflection.quoted_table_name
            )
          end
          
          conditions << interpolated_condition
        end
        
        conditions
      end
      
      def polymorphic_conditions(reflection, polymorphic_reflection)
        if polymorphic_reflection.options[:as]
          "%s.%s = %s" % [
            table_aliases[reflection], "#{polymorphic_reflection.options[:as]}_type",
            @owner.class.quote_value(polymorphic_reflection.active_record.base_class.name)
          ]
        end
      end
      
      def source_type_conditions(reflection)
        if reflection.options[:source_type]
          "%s.%s = %s" % [
            table_aliases[reflection.through_reflection],
            reflection.source_reflection.options[:foreign_type].to_s,
            @owner.class.quote_value(reflection.options[:source_type])
          ]
        end
      end

      # Construct attributes for associate pointing to owner.
      def construct_owner_attributes(reflection)
        if as = reflection.options[:as]
          { "#{as}_id" => @owner.id,
            "#{as}_type" => @owner.class.base_class.name.to_s }
        else
          { reflection.primary_key_name => @owner.id }
        end
      end

      # Construct attributes for :through pointing to owner and associate.
      # This method is used when adding records to the association. Since this only makes sense for
      # non-nested through associations, that's the only case we have to worry about here.
      def construct_join_attributes(associate)
        # TODO: revisit this to allow it for deletion, supposing dependent option is supported
        raise ActiveRecord::HasManyThroughCantAssociateThroughHasOneOrManyReflection.new(@owner, @reflection) if [:has_one, :has_many].include?(@reflection.source_reflection.macro)

        join_attributes = construct_owner_attributes(@reflection.through_reflection).merge(@reflection.source_reflection.primary_key_name => associate.id)

        if @reflection.options[:source_type]
          join_attributes.merge!(@reflection.source_reflection.options[:foreign_type] => associate.class.base_class.name.to_s)
        end

        if @reflection.through_reflection.options[:conditions].is_a?(Hash)
          join_attributes.merge!(@reflection.through_reflection.options[:conditions])
        end

        join_attributes
      end
      
      def ensure_not_nested
        if @reflection.nested?
          raise HasManyThroughNestedAssociationsAreReadonly.new(@owner, @reflection)
        end
      end
    end
  end
end