require 'active_support/core_ext/object/blank'

module ActiveRecord
  module SpawnMethods
    def merge(r)
      return self unless r
      return to_a & r if r.is_a?(Array)

      merged_relation = clone

      r = r.with_default_scope if r.default_scoped? && r.klass != klass

      Relation::ASSOCIATION_METHODS.each do |method|
        value = r.send(:"#{method}_values")

        unless value.empty?
          if method == :includes
            merged_relation = merged_relation.includes(value)
          else
            merge_relation_method(merged_relation, method, value)
          end
        end
      end

      (Relation::MULTI_VALUE_METHODS - [:joins, :where, :order]).each do |method|
        value = r.send(:"#{method}_values")
        merge_relation_method(merged_relation, method, value) if value.present?
      end

      merge_joins(merged_relation, r)

      merged_wheres = @where_values + r.where_values

      unless @where_values.empty?
        # Remove duplicate ARel attributes. Last one wins.
        seen = Hash.new { |h,table| h[table] = {} }
        merged_wheres = merged_wheres.reverse.reject { |w|
          nuke = false
          if w.respond_to?(:operator) && w.operator == :== &&
            w.left.respond_to?(:relation)
            name              = w.left.name
            table             = w.left.relation.name
            nuke              = seen[table][name]
            seen[table][name] = true
          end
          nuke
        }.reverse
      end

      merged_relation.where_values = merged_wheres

      (Relation::SINGLE_VALUE_METHODS - [:lock, :create_with, :reordering]).each do |method|
        value = r.send(:"#{method}_value")
        merged_relation.send(:"#{method}_value=", value) unless value.nil?
      end

      merged_relation.lock_value = r.lock_value unless merged_relation.lock_value

      merged_relation = merged_relation.create_with(r.create_with_value) unless r.create_with_value.empty?

      if (r.reordering_value)
        # override any order specified in the original relation
        merged_relation.reordering_value = true
        merged_relation.order_values = r.order_values
      else
        # merge in order_values from r
        merged_relation.order_values += r.order_values
      end

      # Apply scope extension modules
      merged_relation.send :apply_modules, r.extensions

      merged_relation
    end

    # Removes from the query the condition(s) specified in +skips+.
    #
    # Example:
    #
    #   Post.order('id asc').except(:order)                  # discards the order condition
    #   Post.where('id > 10').order('id asc').except(:where) # discards the where condition but keeps the order
    #
    def except(*skips)
      result = self.class.new(@klass, table)
      result.default_scoped = default_scoped

      ((Relation::ASSOCIATION_METHODS + Relation::MULTI_VALUE_METHODS) - skips).each do |method|
        result.send(:"#{method}_values=", send(:"#{method}_values"))
      end

      (Relation::SINGLE_VALUE_METHODS - skips).each do |method|
        result.send(:"#{method}_value=", send(:"#{method}_value"))
      end

      # Apply scope extension modules
      result.send(:apply_modules, extensions)

      result
    end

    # Removes any condition from the query other than the one(s) specified in +onlies+.
    #
    # Example:
    #
    #   Post.order('id asc').only(:where)         # discards the order condition
    #   Post.order('id asc').only(:where, :order) # uses the specified order
    #
    def only(*onlies)
      result = self.class.new(@klass, table)
      result.default_scoped = default_scoped

      ((Relation::ASSOCIATION_METHODS + Relation::MULTI_VALUE_METHODS) & onlies).each do |method|
        result.send(:"#{method}_values=", send(:"#{method}_values"))
      end

      (Relation::SINGLE_VALUE_METHODS & onlies).each do |method|
        result.send(:"#{method}_value=", send(:"#{method}_value"))
      end

      # Apply scope extension modules
      result.send(:apply_modules, extensions)

      result
    end

    VALID_FIND_OPTIONS = [ :conditions, :include, :joins, :limit, :offset, :extend,
                           :order, :select, :readonly, :group, :having, :from, :lock ]

    def apply_finder_options(options)
      relation = clone
      return relation unless options

      options.assert_valid_keys(VALID_FIND_OPTIONS)
      finders = options.dup
      finders.delete_if { |key, value| value.nil? && key != :limit }

      ([:joins, :select, :group, :order, :having, :limit, :offset, :from, :lock, :readonly] & finders.keys).each do |finder|
        relation = relation.send(finder, finders[finder])
      end

      relation = relation.where(finders[:conditions]) if options.has_key?(:conditions)
      relation = relation.includes(finders[:include]) if options.has_key?(:include)
      relation = relation.extending(finders[:extend]) if options.has_key?(:extend)

      relation
    end

    private

      def merge_joins(relation, other)
        values = other.joins_values
        return if values.blank?

        if other.klass >= relation.klass
          relation.joins_values += values
        else
          joins_dependency, rest = values.partition do |join|
            case join
            when Hash, Symbol, Array
              true
            else
              false
            end
          end

          join_dependency = ActiveRecord::Associations::JoinDependency.new(
            other.klass,
            joins_dependency,
            []
          )

          relation.joins_values += join_dependency.join_associations + rest
        end
      end

      def merge_relation_method(relation, method, value)
        relation.send(:"#{method}_values=", relation.send(:"#{method}_values") + value)
      end
  end
end
