# frozen_string_literal: true

require "active_support/core_ext/hash/except"
require "active_support/core_ext/hash/slice"
require "active_record/relation/merger"

module ActiveRecord
  module SpawnMethods
    def spawn # :nodoc:
      already_in_scope?(klass.scope_registry) ? klass.all : clone
    end

    # Merges in the conditions from <tt>other</tt>, if <tt>other</tt> is an ActiveRecord::Relation.
    # Returns an array representing the intersection of the resulting records with <tt>other</tt>, if <tt>other</tt> is an array.
    #
    #   Post.where(published: true).joins(:comments).merge( Comment.where(spam: false) )
    #   # Performs a single join query with both where conditions.
    #
    #   recent_posts = Post.order('created_at DESC').first(5)
    #   Post.where(published: true).merge(recent_posts)
    #   # Returns the intersection of all published posts with the 5 most recently created posts.
    #   # (This is just an example. You'd probably want to do this with a single query!)
    #
    # Procs will be evaluated by merge:
    #
    #   Post.where(published: true).merge(-> { joins(:comments) })
    #   # => Post.where(published: true).joins(:comments)
    #
    # This is mainly intended for sharing common conditions between multiple associations.
    #
    # For conditions that exist in both relations, those from <tt>other</tt> will take precedence.
    # To find the intersection of two relations, use QueryMethods#and.
    def merge(other, *rest)
      if other.is_a?(Array)
        records & other
      elsif other
        spawn.merge!(other, *rest)
      else
        raise ArgumentError, "invalid argument: #{other.inspect}."
      end
    end

    def merge!(other, *rest) # :nodoc:
      if other.is_a?(Hash)
        Relation::HashMerger.new(self, other).merge
      elsif other.is_a?(Relation)
        Relation::Merger.new(self, other).merge
      elsif other.respond_to?(:to_proc)
        instance_exec(&other)
      else
        raise ArgumentError, "#{other.inspect} is not an ActiveRecord::Relation"
      end
    end

    # Removes from the query the condition(s) specified in +skips+.
    #
    #   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)
      relation_with values.except(*skips)
    end

    # Removes any condition from the query other than the one(s) specified in +onlies+.
    #
    #   Post.order('id asc').only(:where)         # discards the order condition
    #   Post.order('id asc').only(:where, :order) # uses the specified order
    def only(*onlies)
      relation_with values.slice(*onlies)
    end

    private
      def relation_with(values)
        result = spawn
        result.instance_variable_set(:@values, values)
        result
      end
  end
end
