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# Copyright (c) 2005 Rick Olson

# 

# 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.

module ActiveRecord #:nodoc:

  module Acts #:nodoc:

    # Specify this act if you want to save a copy of the row in a versioned table.  This assumes there is a 

    # versioned table ready and that your model has a version field.  This works with optimistic locking if the lock_version

    # column is present as well.

    #

    # The class for the versioned model is derived the first time it is seen. Therefore, if you change your database schema you have to restart

    # your container for the changes to be reflected. In development mode this usually means restarting WEBrick.

    #

    #   class Page < ActiveRecord::Base

    #     # assumes pages_versions table

    #     acts_as_versioned

    #   end

    #

    # Example:

    #

    #   page = Page.create(:title => 'hello world!')

    #   page.version       # => 1

    #

    #   page.title = 'hello world'

    #   page.save

    #   page.version       # => 2

    #   page.versions.size # => 2

    #

    #   page.revert_to(1)  # using version number

    #   page.title         # => 'hello world!'

    #

    #   page.revert_to(page.versions.last) # using versioned instance

    #   page.title         # => 'hello world'

    #

    #   page.versions.earliest # efficient query to find the first version

    #   page.versions.latest   # efficient query to find the most recently created version

    #

    #

    # Simple Queries to page between versions

    #

    #   page.versions.before(version) 

    #   page.versions.after(version)

    #

    # Access the previous/next versions from the versioned model itself

    #

    #   version = page.versions.latest

    #   version.previous # go back one version

    #   version.next     # go forward one version

    #

    # See ActiveRecord::Acts::Versioned::ClassMethods#acts_as_versioned for configuration options

    module Versioned

      CALLBACKS = [:set_new_version, :save_version_on_create, :save_version?, :clear_altered_attributes]

      def self.included(base) # :nodoc:

        base.extend ClassMethods

      end

      module ClassMethods

        # == Configuration options

        #

        # * <tt>class_name</tt> - versioned model class name (default: PageVersion in the above example)

        # * <tt>table_name</tt> - versioned model table name (default: page_versions in the above example)

        # * <tt>foreign_key</tt> - foreign key used to relate the versioned model to the original model (default: page_id in the above example)

        # * <tt>inheritance_column</tt> - name of the column to save the model's inheritance_column value for STI.  (default: versioned_type)

        # * <tt>version_column</tt> - name of the column in the model that keeps the version number (default: version)

        # * <tt>sequence_name</tt> - name of the custom sequence to be used by the versioned model.

        # * <tt>limit</tt> - number of revisions to keep, defaults to unlimited

        # * <tt>if</tt> - symbol of method to check before saving a new version.  If this method returns false, a new version is not saved.

        #   For finer control, pass either a Proc or modify Model#version_condition_met?

        #

        #     acts_as_versioned :if => Proc.new { |auction| !auction.expired? }

        #

        #   or...

        #

        #     class Auction

        #       def version_condition_met? # totally bypasses the <tt>:if</tt> option

        #         !expired?

        #       end

        #     end

        #

        # * <tt>if_changed</tt> - Simple way of specifying attributes that are required to be changed before saving a model.  This takes

        #   either a symbol or array of symbols.  WARNING - This will attempt to overwrite any attribute setters you may have.

        #   Use this instead if you want to write your own attribute setters (and ignore if_changed):

        # 

        #     def name=(new_name)

        #       write_changed_attribute :name, new_name

        #     end

        #

        # * <tt>extend</tt> - Lets you specify a module to be mixed in both the original and versioned models.  You can also just pass a block

        #   to create an anonymous mixin:

        #

        #     class Auction

        #       acts_as_versioned do

        #         def started?

        #           !started_at.nil?

        #         end

        #       end

        #     end

        #

        #   or...

        #

        #     module AuctionExtension

        #       def started?

        #         !started_at.nil?

        #       end

        #     end

        #     class Auction

        #       acts_as_versioned :extend => AuctionExtension

        #     end

        #

        #  Example code:

        #

        #    @auction = Auction.find(1)

        #    @auction.started?

        #    @auction.versions.first.started?

        #

        # == Database Schema

        #

        # The model that you're versioning needs to have a 'version' attribute. The model is versioned 

        # into a table called #{model}_versions where the model name is singlular. The _versions table should 

        # contain all the fields you want versioned, the same version column, and a #{model}_id foreign key field.

        #

        # A lock_version field is also accepted if your model uses Optimistic Locking.  If your table uses Single Table inheritance,

        # then that field is reflected in the versioned model as 'versioned_type' by default.

        #

        # Acts_as_versioned comes prepared with the ActiveRecord::Acts::Versioned::ActMethods::ClassMethods#create_versioned_table 

        # method, perfect for a migration.  It will also create the version column if the main model does not already have it.

        #

        #   class AddVersions < ActiveRecord::Migration

        #     def self.up

        #       # create_versioned_table takes the same options hash

        #       # that create_table does

        #       Post.create_versioned_table

        #     end

        # 

        #     def self.down

        #       Post.drop_versioned_table

        #     end

        #   end

        # 

        # == Changing What Fields Are Versioned

        #

        # By default, acts_as_versioned will version all but these fields: 

        # 

        #   [self.primary_key, inheritance_column, 'version', 'lock_version', versioned_inheritance_column]

        #

        # You can add or change those by modifying #non_versioned_columns.  Note that this takes strings and not symbols.

        #

        #   class Post < ActiveRecord::Base

        #     acts_as_versioned

        #     self.non_versioned_columns << 'comments_count'

        #   end

        # 

        def acts_as_versioned(options = {}, &extension)

          # don't allow multiple calls

          return if self.included_modules.include?(ActiveRecord::Acts::Versioned::ActMethods)

          send :include, ActiveRecord::Acts::Versioned::ActMethods

          cattr_accessor :versioned_class_name, :versioned_foreign_key, :versioned_table_name, :versioned_inheritance_column, 

            :version_column, :max_version_limit, :track_altered_attributes, :version_condition, :version_sequence_name, :non_versioned_columns,

            :version_association_options

          # legacy

          alias_method :non_versioned_fields,  :non_versioned_columns

          alias_method :non_versioned_fields=, :non_versioned_columns=

          class << self

            alias_method :non_versioned_fields,  :non_versioned_columns

            alias_method :non_versioned_fields=, :non_versioned_columns=

          end

          send :attr_accessor, :altered_attributes

          self.versioned_class_name         = options[:class_name]  || "Version"

          self.versioned_foreign_key        = options[:foreign_key] || self.to_s.foreign_key

          self.versioned_table_name         = options[:table_name]  || "#{table_name_prefix}#{base_class.name.demodulize.underscore}_versions#{table_name_suffix}"

          self.versioned_inheritance_column = options[:inheritance_column] || "versioned_#{inheritance_column}"

          self.version_column               = options[:version_column]     || 'version'

          self.version_sequence_name        = options[:sequence_name]

          self.max_version_limit            = options[:limit].to_i

          self.version_condition            = options[:if] || true

          self.non_versioned_columns        = [self.primary_key, inheritance_column, 'version', 'lock_version', versioned_inheritance_column]

          self.version_association_options  = {

                                                :class_name  => "#{self.to_s}::#{versioned_class_name}",

                                                :foreign_key => versioned_foreign_key,

                                                :dependent   => :delete_all

                                              }.merge(options[:association_options] || {})

          if block_given?

            extension_module_name = "#{versioned_class_name}Extension"

            silence_warnings do

              self.const_set(extension_module_name, Module.new(&extension))

            end

            options[:extend] = self.const_get(extension_module_name)

          end

          class_eval do

            has_many :versions, version_association_options do

              # finds earliest version of this record

              def earliest

                @earliest ||= find(:first, :order => 'version')

              end

              # find latest version of this record

              def latest

                @latest ||= find(:first, :order => 'version desc')

              end

            end

            before_save  :set_new_version

            after_create :save_version_on_create

            after_update :save_version

            after_save   :clear_old_versions

            after_save   :clear_altered_attributes

            unless options[:if_changed].nil?

              self.track_altered_attributes = true

              options[:if_changed] = [options[:if_changed]] unless options[:if_changed].is_a?(Array)

              options[:if_changed].each do |attr_name|

                define_method("#{attr_name}=") do |value|

                  write_changed_attribute attr_name, value

                end

              end

            end

            include options[:extend] if options[:extend].is_a?(Module)

          end

          # create the dynamic versioned model

          const_set(versioned_class_name, Class.new(ActiveRecord::Base)).class_eval do

            def self.reloadable? ; false ; end

            # find first version before the given version

            def self.before(version)

              find :first, :order => 'version desc',

                :conditions => ["#{original_class.versioned_foreign_key} = ? and version < ?", version.send(original_class.versioned_foreign_key), version.version]

            end

            # find first version after the given version.

            def self.after(version)

              find :first, :order => 'version',

                :conditions => ["#{original_class.versioned_foreign_key} = ? and version > ?", version.send(original_class.versioned_foreign_key), version.version]

            end

            def previous

              self.class.before(self)

            end

            def next

              self.class.after(self)

            end

            def versions_count

              page.version

            end

          end

          versioned_class.cattr_accessor :original_class

          versioned_class.original_class = self

          versioned_class.set_table_name versioned_table_name

          versioned_class.belongs_to self.to_s.demodulize.underscore.to_sym, 

            :class_name  => "::#{self.to_s}", 

            :foreign_key => versioned_foreign_key

          versioned_class.send :include, options[:extend]         if options[:extend].is_a?(Module)

          versioned_class.set_sequence_name version_sequence_name if version_sequence_name

        end

      end

      module ActMethods

        def self.included(base) # :nodoc:

          base.extend ClassMethods

        end

        # Finds a specific version of this record

        def find_version(version = nil)

          self.class.find_version(id, version)

        end

        # Saves a version of the model if applicable

        def save_version

          save_version_on_create if save_version?

        end

        # Saves a version of the model in the versioned table.  This is called in the after_save callback by default

        def save_version_on_create

          rev = self.class.versioned_class.new

          self.clone_versioned_model(self, rev)

          rev.version = send(self.class.version_column)

          rev.send("#{self.class.versioned_foreign_key}=", self.id)

          rev.save

        end

        # Clears old revisions if a limit is set with the :limit option in <tt>acts_as_versioned</tt>.

        # Override this method to set your own criteria for clearing old versions.

        def clear_old_versions

          return if self.class.max_version_limit == 0

          excess_baggage = send(self.class.version_column).to_i - self.class.max_version_limit

          if excess_baggage > 0

            sql = "DELETE FROM #{self.class.versioned_table_name} WHERE version <= #{excess_baggage} AND #{self.class.versioned_foreign_key} = #{self.id}"

            self.class.versioned_class.connection.execute sql

          end

        end

        def versions_count

          version

        end

        # Reverts a model to a given version.  Takes either a version number or an instance of the versioned model

        def revert_to(version)

          if version.is_a?(self.class.versioned_class)

            return false unless version.send(self.class.versioned_foreign_key) == self.id and !version.new_record?

          else

            return false unless version = versions.find_by_version(version)

          end

          self.clone_versioned_model(version, self)

          self.send("#{self.class.version_column}=", version.version)

          true

        end

        # Reverts a model to a given version and saves the model.

        # Takes either a version number or an instance of the versioned model

        def revert_to!(version)

          revert_to(version) ? save_without_revision : false

        end

        # Temporarily turns off Optimistic Locking while saving.  Used when reverting so that a new version is not created.

        def save_without_revision

          save_without_revision!

          true

        rescue

          false

        end

        def save_without_revision!

          without_locking do

            without_revision do

              save!

            end

          end

        end

        # Returns an array of attribute keys that are versioned.  See non_versioned_columns

        def versioned_attributes

          self.attributes.keys.select { |k| !self.class.non_versioned_columns.include?(k) }

        end

        # If called with no parameters, gets whether the current model has changed and needs to be versioned.

        # If called with a single parameter, gets whether the parameter has changed.

        def changed?(attr_name = nil)

          attr_name.nil? ?

            (!self.class.track_altered_attributes || (altered_attributes && altered_attributes.length > 0)) :

            (altered_attributes && altered_attributes.include?(attr_name.to_s))

        end

        # keep old dirty? method

        alias_method :dirty?, :changed?

        # Clones a model.  Used when saving a new version or reverting a model's version.

        def clone_versioned_model(orig_model, new_model)

          self.versioned_attributes.each do |key|

            new_model.send("#{key}=", orig_model.send(key)) if orig_model.has_attribute?(key)

          end

          if orig_model.is_a?(self.class.versioned_class)

            new_model[new_model.class.inheritance_column] = orig_model[self.class.versioned_inheritance_column]

          elsif new_model.is_a?(self.class.versioned_class)

            new_model[self.class.versioned_inheritance_column] = orig_model[orig_model.class.inheritance_column]

          end

        end

        # Checks whether a new version shall be saved or not.  Calls <tt>version_condition_met?</tt> and <tt>changed?</tt>.

        def save_version?

          version_condition_met? && changed?

        end

        # Checks condition set in the :if option to check whether a revision should be created or not.  Override this for

        # custom version condition checking.

        def version_condition_met?

          case

          when version_condition.is_a?(Symbol)

            send(version_condition)

          when version_condition.respond_to?(:call) && (version_condition.arity == 1 || version_condition.arity == -1)

            version_condition.call(self)

          else

            version_condition

          end

        end

        # Executes the block with the versioning callbacks disabled.

        #

        #   @foo.without_revision do

        #     @foo.save

        #   end

        #

        def without_revision(&block)

          self.class.without_revision(&block)

        end

        # Turns off optimistic locking for the duration of the block

        #

        #   @foo.without_locking do

        #     @foo.save

        #   end

        #

        def without_locking(&block)

          self.class.without_locking(&block)

        end

        def empty_callback() end #:nodoc:

        protected

          # sets the new version before saving, unless you're using optimistic locking.  In that case, let it take care of the version.

          def set_new_version

            self.send("#{self.class.version_column}=", self.next_version) if new_record? || (!locking_enabled? && save_version?)

          end

          # Gets the next available version for the current record, or 1 for a new record

          def next_version

            return 1 if new_record?

            (versions.calculate(:max, :version) || 0) + 1

          end

          # clears current changed attributes.  Called after save.

          def clear_altered_attributes

            self.altered_attributes = []

          end

          def write_changed_attribute(attr_name, attr_value)

            # Convert to db type for comparison. Avoids failing Float<=>String comparisons.

            attr_value_for_db = self.class.columns_hash[attr_name.to_s].type_cast(attr_value)

            (self.altered_attributes ||= []) << attr_name.to_s unless self.changed?(attr_name) || self.send(attr_name) == attr_value_for_db

            write_attribute(attr_name, attr_value_for_db)

          end

        module ClassMethods

          # Finds a specific version of a specific row of this model

          def find_version(id, version = nil)

            return find(id) unless version

            conditions = ["#{versioned_foreign_key} = ? AND version = ?", id, version]

            options = { :conditions => conditions, :limit => 1 }

            if result = find_versions(id, options).first

              result

            else

              raise RecordNotFound, "Couldn't find #{name} with ID=#{id} and VERSION=#{version}"

            end

          end

          # Finds versions of a specific model.  Takes an options hash like <tt>find</tt>

          def find_versions(id, options = {})

            versioned_class.find :all, {

              :conditions => ["#{versioned_foreign_key} = ?", id],

              :order      => 'version' }.merge(options)

          end

          # Returns an array of columns that are versioned.  See non_versioned_columns

          def versioned_columns

            self.columns.select { |c| !non_versioned_columns.include?(c.name) }

          end

          # Returns an instance of the dynamic versioned model

          def versioned_class

            const_get versioned_class_name

          end

          # Rake migration task to create the versioned table using options passed to acts_as_versioned

          def create_versioned_table(create_table_options = {})

            # create version column in main table if it does not exist

            if !self.content_columns.find { |c| %w(version lock_version).include? c.name }

              self.connection.add_column table_name, :version, :integer

            end

            self.connection.create_table(versioned_table_name, create_table_options) do |t|

              t.column versioned_foreign_key, :integer

              t.column :version, :integer

            end

            updated_col = nil

            self.versioned_columns.each do |col| 

              updated_col = col if !updated_col && %(updated_at updated_on).include?(col.name)

              self.connection.add_column versioned_table_name, col.name, col.type, 

                :limit => col.limit, 

                :default => col.default,

                :scale => col.scale,

                :precision => col.precision

            end

            if type_col = self.columns_hash[inheritance_column]

              self.connection.add_column versioned_table_name, versioned_inheritance_column, type_col.type, 

                :limit => type_col.limit, 

                :default => type_col.default,

                :scale => type_col.scale,

                :precision => type_col.precision

            end

            if updated_col.nil?

              self.connection.add_column versioned_table_name, :updated_at, :timestamp

            end

          end

          # Rake migration task to drop the versioned table

          def drop_versioned_table

            self.connection.drop_table versioned_table_name

          end

          # Executes the block with the versioning callbacks disabled.

          #

          #   Foo.without_revision do

          #     @foo.save

          #   end

          #

          def without_revision(&block)

            class_eval do 

              CALLBACKS.each do |attr_name|

                alias_method "orig_#{attr_name}".to_sym, attr_name

                alias_method attr_name, :empty_callback

              end

            end

            block.call

          ensure

            class_eval do 

              CALLBACKS.each do |attr_name|

                alias_method attr_name, "orig_#{attr_name}".to_sym

              end

            end

          end

          # Turns off optimistic locking for the duration of the block

          #

          #   Foo.without_locking do

          #     @foo.save

          #   end

          #

          def without_locking(&block)

            current = ActiveRecord::Base.lock_optimistically

            ActiveRecord::Base.lock_optimistically = false if current

            result = block.call

            ActiveRecord::Base.lock_optimistically = true if current

            result

          end

        end

      end

    end

  end

end

ActiveRecord::Base.send :include, ActiveRecord::Acts::Versioned