Add support for callbacks

1 files changed, 477 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/new_callbacks.rb b/activesupport/lib/active_support/new_callbacks.rb
new file mode 100644
index 0000000000..cf717bfbb9
--- /dev/null
+++ b/activesupport/lib/active_support/new_callbacks.rb
@@ -0,0 +1,477 @@
+module ActiveSupport
+  # Callbacks are hooks into the lifecycle of an object that allow you to trigger logic
+  # before or after an alteration of the object state.
+  #
+  # Mixing in this module allows you to define callbacks in your class.
+  #
+  # Example:
+  #   class Storage
+  #     include ActiveSupport::Callbacks
+  #
+  #     define_callbacks :save
+  #   end
+  #
+  #   class ConfigStorage < Storage
+  #     save_callback :before, :saving_message
+  #     def saving_message
+  #       puts "saving..."
+  #     end
+  #
+  #     save_callback :after do |object|
+  #       puts "saved"
+  #     end
+  #
+  #     def save
+  #       _run_save_callbacks do
+  #         puts "- save"
+  #       end
+  #     end
+  #   end
+  #
+  #   config = ConfigStorage.new
+  #   config.save
+  #
+  # Output:
+  #   saving...
+  #   - save
+  #   saved
+  #
+  # Callbacks from parent classes are inherited.
+  #
+  # Example:
+  #   class Storage
+  #     include ActiveSupport::Callbacks
+  #
+  #     define_callbacks :save
+  #
+  #     save_callback :before, :prepare
+  #     def prepare
+  #       puts "preparing save"
+  #     end
+  #   end
+  #
+  #   class ConfigStorage < Storage
+  #     save_callback :before, :saving_message
+  #     def saving_message
+  #       puts "saving..."
+  #     end
+  #
+  #     save_callback :after do |object|
+  #       puts "saved"
+  #     end
+  #
+  #     def save
+  #       _run_save_callbacks do
+  #         puts "- save"
+  #       end
+  #     end
+  #   end
+  #
+  #   config = ConfigStorage.new
+  #   config.save
+  #
+  # Output:
+  #   preparing save
+  #   saving...
+  #   - save
+  #   saved
+  module NewCallbacks
+    def self.included(klass)
+      klass.extend ClassMethods
+    end
+        
+    def run_callbacks(kind, options = {}, &blk)
+      send("_run_#{kind}_callbacks", &blk)
+    end
+    
+    class Callback
+      @@_callback_sequence = 0
+      
+      attr_accessor :filter, :kind, :name, :options, :per_key, :klass
+      def initialize(filter, kind, options, klass, name)
+        @kind, @klass = kind, klass
+        @name         = name
+        
+        normalize_options!(options)
+
+        @per_key              = options.delete(:per_key)
+        @raw_filter, @options = filter, options
+        @filter               = _compile_filter(filter)
+        @compiled_options     = _compile_options(options)
+        @callback_id          = next_id
+
+        _compile_per_key_options
+      end
+      
+      def clone(klass)
+        obj                  = super()
+        obj.klass            = klass
+        obj.per_key          = @per_key.dup
+        obj.options          = @options.dup
+        obj.per_key[:if]     = @per_key[:if].dup
+        obj.per_key[:unless] = @per_key[:unless].dup
+        obj.options[:if]     = @options[:if].dup
+        obj.options[:unless] = @options[:unless].dup
+        obj
+      end
+      
+      def normalize_options!(options)
+        options[:if] = Array(options[:if])
+        options[:unless] = Array(options[:unless])
+
+        options[:per_key] ||= {}
+        options[:per_key][:if] = Array(options[:per_key][:if])
+        options[:per_key][:unless] = Array(options[:per_key][:unless])
+      end
+      
+      def next_id
+        @@_callback_sequence += 1
+      end
+      
+      def matches?(_kind, _name, _filter)
+        @kind   == _kind &&
+        @name   == _name &&
+        @filter == _filter
+      end
+
+      def _update_filter(filter_options, new_options)
+        filter_options[:if].push(new_options[:unless]) if new_options.key?(:unless)
+        filter_options[:unless].push(new_options[:if]) if new_options.key?(:if)
+      end
+            
+      def recompile!(_options, _per_key)
+        _update_filter(self.options, _options)
+        _update_filter(self.per_key, _per_key)
+        
+        @callback_id      = next_id
+        @filter           = _compile_filter(@raw_filter)
+        @compiled_options = _compile_options(@options)
+                            _compile_per_key_options
+      end
+
+      def _compile_per_key_options
+        key_options  = _compile_options(@per_key)
+
+        @klass.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
+          def _one_time_conditions_valid_#{@callback_id}?
+            true #{key_options[0]}
+          end
+        RUBY_EVAL
+      end
+      
+      # This will supply contents for before and around filters, and no
+      # contents for after filters (for the forward pass).
+      def start(key = nil, options = {})
+        object, terminator = (options || {}).values_at(:object, :terminator)
+        
+        return if key && !object.send("_one_time_conditions_valid_#{@callback_id}?")
+        
+        terminator ||= false
+        
+        # options[0] is the compiled form of supplied conditions
+        # options[1] is the "end" for the conditional
+                
+        if @kind == :before || @kind == :around
+          if @kind == :before
+            # if condition    # before_save :filter_name, :if => :condition
+            #   filter_name
+            # end
+            filter = <<-RUBY_EVAL
+              unless halted
+                result = #{@filter}
+                halted ||= (#{terminator})
+              end
+            RUBY_EVAL
+            [@compiled_options[0], filter, @compiled_options[1]].compact.join("\n")
+          else
+            # Compile around filters with conditions into proxy methods
+            # that contain the conditions.
+            #
+            # For `around_save :filter_name, :if => :condition':
+            #
+            # def _conditional_callback_save_17
+            #   if condition
+            #     filter_name do
+            #       yield self
+            #     end
+            #   else
+            #     yield self
+            #   end
+            # end
+            
+            name = "_conditional_callback_#{@kind}_#{next_id}"
+            txt = <<-RUBY_EVAL
+              def #{name}(halted)
+                #{@compiled_options[0] || "if true"} && !halted
+                  #{@filter} do
+                    yield self
+                  end
+                else
+                  yield self
+                end
+              end
+            RUBY_EVAL
+            @klass.class_eval(txt)
+            "#{name}(halted) do"
+          end
+        end
+      end
+      
+      # This will supply contents for around and after filters, but not
+      # before filters (for the backward pass).
+      def end(key = nil, options = {})
+        object = (options || {})[:object]
+        
+        return if key && !object.send("_one_time_conditions_valid_#{@callback_id}?")
+        
+        if @kind == :around || @kind == :after
+          # if condition    # after_save :filter_name, :if => :condition
+          #   filter_name
+          # end
+          if @kind == :after
+            [@compiled_options[0], @filter, @compiled_options[1]].compact.join("\n")
+          else
+            "end"
+          end
+        end
+      end
+      
+      private
+      # Options support the same options as filters themselves (and support
+      # symbols, string, procs, and objects), so compile a conditional
+      # expression based on the options
+      def _compile_options(options)        
+        return [] if options[:if].empty? && options[:unless].empty?
+        
+        conditions = []
+        
+        unless options[:if].empty?
+          conditions << Array(_compile_filter(options[:if]))
+        end
+        
+        unless options[:unless].empty?
+          conditions << Array(_compile_filter(options[:unless])).map {|f| "!#{f}"}
+        end
+        
+        ["if #{conditions.flatten.join(" && ")}", "end"]
+      end
+      
+      # Filters support:
+      #   Arrays::  Used in conditions. This is used to specify
+      #             multiple conditions. Used internally to
+      #             merge conditions from skip_* filters
+      #   Symbols:: A method to call
+      #   Strings:: Some content to evaluate
+      #   Procs::   A proc to call with the object
+      #   Objects:: An object with a before_foo method on it to call
+      #
+      # All of these objects are compiled into methods and handled
+      # the same after this point:
+      #   Arrays::  Merged together into a single filter
+      #   Symbols:: Already methods
+      #   Strings:: class_eval'ed into methods
+      #   Procs::   define_method'ed into methods
+      #   Objects:: 
+      #     a method is created that calls the before_foo method
+      #     on the object.
+      def _compile_filter(filter)
+        method_name = "_callback_#{@kind}_#{next_id}"
+        case filter
+        when Array
+          filter.map {|f| _compile_filter(f)}
+        when Symbol
+          filter
+        when Proc
+          @klass.send(:define_method, method_name, &filter)
+          method_name << (filter.arity == 1 ? "(self)" : "")
+        when String
+          @klass.class_eval <<-RUBY_EVAL
+            def #{method_name}
+              #{filter}
+            end
+          RUBY_EVAL
+          method_name
+        else
+          kind, name = @kind, @name
+          @klass.send(:define_method, method_name) do
+            filter.send("#{kind}_#{name}", self)
+          end
+          method_name
+        end
+      end
+    end
+
+    # This method_missing is supplied to catch callbacks with keys and create
+    # the appropriate callback for future use.
+    def method_missing(meth, *args, &blk)
+      if meth.to_s =~ /_run__([\w:]+)__(\w+)__(\w+)__callbacks/
+        return self.class._create_and_run_keyed_callback($1, $2.to_sym, $3.to_sym, self, &blk)
+      end
+      super
+    end
+    
+    # An Array with a compile method
+    class CallbackChain < Array
+      def initialize(symbol)
+        @symbol = symbol
+      end
+      
+      def compile(key = nil, options = {})
+        method = []
+        method << "halted = false"
+        each do |callback|
+          method << callback.start(key, options)
+        end
+        method << "yield self if block_given?"
+        reverse_each do |callback|
+          method << callback.end(key, options)
+        end
+        method.compact.join("\n")
+      end
+      
+      def clone(klass)
+        chain = CallbackChain.new(@symbol)
+        chain.push(*map {|c| c.clone(klass)})
+      end
+    end
+        
+    module ClassMethods
+      CHAINS = {:before => :before, :around => :before, :after => :after}
+      
+      # Make the _run_save_callbacks method. The generated method takes
+      # a block that it'll yield to. It'll call the before and around filters
+      # in order, yield the block, and then run the after filters.
+      # 
+      # _run_save_callbacks do
+      #   save
+      # end
+      #
+      # The _run_save_callbacks method can optionally take a key, which
+      # will be used to compile an optimized callback method for each
+      # key. See #define_callbacks for more information.
+      def _define_runner(symbol, str, options)
+        str = <<-RUBY_EVAL
+          def _run_#{symbol}_callbacks(key = nil)
+            if key
+              send("_run__\#{self.class.name.split("::").last}__#{symbol}__\#{key}__callbacks") { yield if block_given? }
+            else
+              #{str}
+            end
+          end
+        RUBY_EVAL
+  
+        class_eval str, __FILE__, __LINE__ + 1
+        
+        before_name, around_name, after_name = 
+          options.values_at(:before, :after, :around)
+      end
+      
+      # This is called the first time a callback is called with a particular
+      # key. It creates a new callback method for the key, calculating
+      # which callbacks can be omitted because of per_key conditions.
+      def _create_and_run_keyed_callback(klass, kind, key, obj, &blk)
+        @_keyed_callbacks ||= {}
+        @_keyed_callbacks[[kind, key]] ||= begin
+          str = self.send("_#{kind}_callbacks").compile(key, :object => obj, :terminator => self.send("_#{kind}_terminator"))
+                              
+          self.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
+            def _run__#{klass.split("::").last}__#{kind}__#{key}__callbacks
+              #{str}
+            end
+          RUBY_EVAL
+                    
+          true
+        end
+                                  
+        obj.send("_run__#{klass.split("::").last}__#{kind}__#{key}__callbacks", &blk)
+      end
+      
+      # Define callbacks.
+      #
+      # Creates a <name>_callback method that you can use to add callbacks.
+      #
+      # Syntax:
+      #   save_callback :before, :before_meth
+      #   save_callback :after,  :after_meth, :if => :condition
+      #   save_callback :around {|r| stuff; yield; stuff }
+      #
+      # The <name>_callback method also updates the _run_<name>_callbacks
+      # method, which is the public API to run the callbacks.
+      #
+      # Also creates a skip_<name>_callback method that you can use to skip
+      # callbacks.
+      #
+      # When creating or skipping callbacks, you can specify conditions that
+      # are always the same for a given key. For instance, in ActionPack,
+      # we convert :only and :except conditions into per-key conditions.
+      #
+      #   before_filter :authenticate, :except => "index"
+      # becomes
+      #   dispatch_callback :before, :authenticate, :per_key => {:unless => proc {|c| c.action_name == "index"}}
+      #
+      # Per-Key conditions are evaluated only once per use of a given key.
+      # In the case of the above example, you would do:
+      #
+      #   run_dispatch_callbacks(action_name) { ... dispatch stuff ... }
+      #
+      # In that case, each action_name would get its own compiled callback
+      # method that took into consideration the per_key conditions. This
+      # is a speed improvement for ActionPack.
+      def define_callbacks(*symbols)
+        terminator = symbols.pop if symbols.last.is_a?(String)
+        symbols.each do |symbol|
+          self.class_inheritable_accessor("_#{symbol}_terminator")
+          self.send("_#{symbol}_terminator=", terminator)
+          self.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
+            class_inheritable_accessor :_#{symbol}_callbacks
+            self._#{symbol}_callbacks = CallbackChain.new(:#{symbol})
+
+            def self.#{symbol}_callback(*filters, &blk)
+              type = [:before, :after, :around].include?(filters.first) ? filters.shift : :before
+              options = filters.last.is_a?(Hash) ? filters.pop : {}
+              filters.unshift(blk) if block_given?
+              
+              filters.map! do |filter| 
+                # overrides parent class
+                self._#{symbol}_callbacks.delete_if {|c| c.matches?(type, :#{symbol}, filter)}
+                Callback.new(filter, type, options.dup, self, :#{symbol})
+              end
+              self._#{symbol}_callbacks.push(*filters)
+              _define_runner(:#{symbol}, 
+                self._#{symbol}_callbacks.compile(nil, :terminator => _#{symbol}_terminator), 
+                options)
+            end
+            
+            def self.skip_#{symbol}_callback(*filters, &blk)
+              type = [:before, :after, :around].include?(filters.first) ? filters.shift : :before
+              options = filters.last.is_a?(Hash) ? filters.pop : {}
+              filters.unshift(blk) if block_given?
+              filters.each do |filter|
+                self._#{symbol}_callbacks = self._#{symbol}_callbacks.clone(self)
+                
+                filter = self._#{symbol}_callbacks.find {|c| c.matches?(type, :#{symbol}, filter) }
+                per_key = options[:per_key] || {}
+                if filter
+                  filter.recompile!(options, per_key)
+                else
+                  self._#{symbol}_callbacks.delete(filter)
+                end
+                _define_runner(:#{symbol}, 
+                  self._#{symbol}_callbacks.compile(nil, :terminator => _#{symbol}_terminator), 
+                  options)
+              end
+              
+            end
+            
+            def self.reset_#{symbol}_callbacks
+              self._#{symbol}_callbacks = CallbackChain.new(:#{symbol})
+              _define_runner(:#{symbol}, self._#{symbol}_callbacks.compile, {})
+            end
+            
+            self.#{symbol}_callback(:before)
+          RUBY_EVAL
+        end
+      end
+    end
+  end
+end