couchrest_model/lib/couchrest/mixins/callbacks.rb

# Copyright (c) 2006-2009 David Heinemeier Hansson
#  
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#  
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#  
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
#
# Extracted from ActiveSupport::NewCallbacks written by Yehuda Katz
# http://github.com/rails/rails/raw/d6e4113c83a9d55be6f2af247da2cecaa855f43b/activesupport/lib/active_support/new_callbacks.rb
# http://github.com/rails/rails/commit/1126a85aed576402d978e6f76eb393b6baaa9541

require File.join(File.dirname(__FILE__), '..', 'support', 'class')

module CouchRest
  # 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 Callbacks
    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)
        @kind, @klass = kind, klass

        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.wrap(options[:if])
        options[:unless] = Array.wrap(options[:unless])

        options[:per_key] ||= {}
        options[:per_key][:if] = Array.wrap(options[:per_key][:if])
        options[:per_key][:unless] = Array.wrap(options[:per_key][:unless])
      end

      def next_id
        @@_callback_sequence += 1
      end

      def matches?(_kind, _filter)
        @kind   == _kind &&
        @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, line = <<-RUBY_EVAL, __LINE__ + 1
              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, __FILE__, line)
            "#{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.wrap(_compile_filter(options[:if]))
        end

        unless options[:unless].empty?
          conditions << Array.wrap(_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 String
          "(#{filter})"
        when Proc
          @klass.send(:define_method, method_name, &filter)
          return method_name if filter.arity == 0

          method_name << (filter.arity == 1 ? "(self)" : " self, Proc.new ")
        else
          @klass.send(:define_method, "#{method_name}_object") { filter }

          _normalize_legacy_filter(kind, filter)

          @klass.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
            def #{method_name}(&blk)
              #{method_name}_object.send(:#{kind}, self, &blk)
            end
          RUBY_EVAL

          method_name
        end
      end

      def _normalize_legacy_filter(kind, filter)
        if !filter.respond_to?(kind) && filter.respond_to?(:filter)
          filter.class_eval(
            "def #{kind}(context, &block) filter(context, &block) end",
            __FILE__, __LINE__ - 1)
        elsif filter.respond_to?(:before) && filter.respond_to?(:after) && kind == :around
          def filter.around(context)
            should_continue = before(context)
            yield if should_continue
            after(context)
          end
        end
      end

    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? && !halted"
        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)
        body = send("_#{symbol}_callback").
          compile(nil, :terminator => send("_#{symbol}_terminator"))

        body, line = <<-RUBY_EVAL, __LINE__ + 1
          def _run_#{symbol}_callbacks(key = nil, &blk)
            if key
              name = "_run__\#{self.class.name.hash.abs}__#{symbol}__\#{key.hash.abs}__callbacks"

              unless respond_to?(name)
                self.class._create_keyed_callback(name, :#{symbol}, self, &blk)
              end

              send(name, &blk)
            else
              #{body}
            end
          end
        RUBY_EVAL

        undef_method "_run_#{symbol}_callbacks" if method_defined?("_run_#{symbol}_callbacks")
        class_eval body, __FILE__, line
      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_keyed_callback(name, kind, obj, &blk)
        @_keyed_callbacks ||= {}
        @_keyed_callbacks[name] ||= begin
          str = send("_#{kind}_callback").
            compile(name, :object => obj, :terminator => send("_#{kind}_terminator"))

          class_eval "def #{name}() #{str} end", __FILE__, __LINE__

          true
        end
      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 _update_callbacks(name, filters = CallbackChain.new(name), block = nil)
        type = [:before, :after, :around].include?(filters.first) ? filters.shift : :before
        options = filters.last.is_a?(Hash) ? filters.pop : {}
        filters.unshift(block) if block

        callbacks = send("_#{name}_callback")
        yield callbacks, type, filters, options if block_given?

        _define_runner(name)
      end

      alias_method :_reset_callbacks, :_update_callbacks

      def set_callback(name, *filters, &block)
        _update_callbacks(name, filters, block) do |callbacks, type, filters, options|        
          filters.map! do |filter|
            # overrides parent class
            callbacks.delete_if {|c| c.matches?(type, filter) }
            Callback.new(filter, type, options.dup, self)
          end

          options[:prepend] ? callbacks.unshift(*filters) : callbacks.push(*filters)
        end
      end

      def skip_callback(name, *filters, &block)
        _update_callbacks(name, filters, block) do |callbacks, type, filters, options|
          filters.each do |filter|
            callbacks = send("_#{name}_callback=", callbacks.clone(self))

            filter = callbacks.find {|c| c.matches?(type, filter) }

            if filter && options.any?
              filter.recompile!(options, options[:per_key] || {})
            else
              callbacks.delete(filter)
            end
          end
        end
      end

      def define_callbacks(*symbols)
        terminator = symbols.pop if symbols.last.is_a?(String)
        symbols.each do |symbol|
          extlib_inheritable_accessor("_#{symbol}_terminator") { terminator }

          extlib_inheritable_accessor("_#{symbol}_callback") do
            CallbackChain.new(symbol)
          end

          _define_runner(symbol)
          
          # Define more convenient callback methods
          # set_callback(:save, :before) becomes before_save
          [:before, :after, :around].each do |filter|
            self.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
              def self.#{filter}_#{symbol}(*symbols, &blk)
                _alias_callbacks(symbols, blk) do |callback, options|
                  set_callback(:#{symbol}, :#{filter}, callback, options)
                end
              end
            RUBY_EVAL
          end
        end
      end
      
      def _alias_callbacks(callbacks, block)
        options = callbacks.last.is_a?(Hash) ? callbacks.pop : {}
        callbacks.push(block) if block
        callbacks.each do |callback|
          yield callback, options
        end
      end
    end
  end
end