module Sequel
  class Dataset
    # ---------------------
    # :section: 7 - Mutation methods
    # These methods modify the receiving dataset and should be used with care.
    # ---------------------
    
    # All methods that should have a ! method added that modifies the receiver.
    MUTATION_METHODS = QUERY_METHODS - [:paginate, :naked, :from_self]
    
    # Setup mutation (e.g. filter!) methods.  These operate the same as the
    # non-! methods, but replace the options of the current dataset with the
    # options of the resulting dataset.
    #
    # Do not call this method with untrusted input, as that can result in
    # arbitrary code execution.
    def self.def_mutation_method(*meths)
      options = meths.pop if meths.last.is_a?(Hash)
      mod = options[:module] if options
      mod ||= self
      meths.each do |meth|
        mod.class_eval("def #{meth}!(*args, &block); mutation_method(:#{meth}, *args, &block) end", __FILE__, __LINE__)
      end
    end
    
    # Add the mutation methods via metaprogramming
    def_mutation_method(*MUTATION_METHODS)
    
    # Set the method to call on identifiers going into the database for this dataset
    attr_writer :identifier_input_method
    
    # Set the method to call on identifiers coming the database for this dataset
    attr_writer :identifier_output_method

    # Whether to quote identifiers for this dataset
    attr_writer :quote_identifiers
    
    # The row_proc for this database, should be any object that responds to +call+ with
    # a single hash argument and returns the object you want #each to return.
    attr_accessor :row_proc
    
    # Load an extension into the receiver.  In addition to requiring the extension file, this
    # also modifies the dataset to work with the extension (usually extending it with a
    # module defined in the extension file).  If no related extension file exists or the
    # extension does not have specific support for Database objects, an Error will be raised.
    # Returns self.
    def extension!(*exts)
      Sequel.extension(*exts)
      exts.each do |ext|
        if pr = Sequel.synchronize{EXTENSIONS[ext]}
          pr.call(self)
        else
          raise(Error, "Extension #{ext} does not have specific support handling individual datasets")
        end
      end
      self
    end

    # Avoid self-referential dataset by cloning.
    def from_self!(*args, &block)
      @opts.merge!(clone.from_self(*args, &block).opts)
      self
    end

    # Remove the row_proc from the current dataset.
    def naked!
      self.row_proc = nil
      self
    end
    
    private
    
    # Modify the receiver with the results of sending the meth, args, and block
    # to the receiver and merging the options of the resulting dataset into
    # the receiver's options.
    def mutation_method(meth, *args, &block)
      copy = send(meth, *args, &block)
      @opts.merge!(copy.opts)
      self
    end
  end
end