jbarnette · February 28, 2012 18:45 · Feb 28, 2012
diff --git a/gistfile1.txt b/gistfile1.txt
@@ -0,0 +1,154 @@
+require "overlord/searchable"
+
+module Overlord
+
+  # Mark an ActiveRecord model as having a state machine. Requires a
+  # string attribute called `state`. To set the default state for a
+  # class, set a default column value for `state` in the database.
+  #
+  # Use Symbols for all keys and values in state definitions.
+
+  module Stateful
+    ANY = Object.new
+
+    def self.included model
+      model.validates :state, presence: true
+
+      model.extend Macro
+
+      model.stateful do
+        state :active
+        state :inactive
+        state :deleted
+
+        on :activate do
+          move :inactive => :active
+        end
+
+        on :deactivate do
+          move :active => :inactive
+        end
+
+        on :delete do
+          move any => :deleted
+        end
+      end
+
+      if model < Overlord::Searchable
+        Sunspot.setup model do
+          string :state, stored: true
+        end
+      end
+    end
+
+    module Macro
+      def machine
+        @machine ||= Machine.new self
+      end
+
+      def stateful &block
+        machine.instance_eval(&block)
+      end
+    end
+
+    class Context < Struct.new :instance, :event, :src, :dest, :args
+      def trigger hooks
+        hooks.values_at(dest, ANY).compact.flatten.each do |hook|
+          instance.instance_exec self, &hook
+        end
+      end
+    end
+
+    class Event
+      def initialize model, name
+        @moves = {}
+
+        model.send :define_method, "#{name}!" do |*args|
+          model.machine.fire self, name, *args
+        end
+      end
+
+      def any
+        ANY
+      end
+
+      def dest current
+        @moves[current.to_sym] || @moves[any]
+      end
+
+      def move pair
+        Array(pair.keys.first).each do |s|
+          @moves[s] = pair.values.first
+        end
+      end
+    end
+
+    class Machine
+      def initialize model
+        @model     = model
+        @entered   = Hash.new { |h, k| h[k] = [] }
+        @entering  = Hash.new { |h, k| h[k] = [] }
+        @events    = Hash.new { |h, k| h[k] = Event.new @model, k }
+        @persisted = Hash.new { |h, k| h[k] = [] }
+      end
+
+      def entered *names, &block
+        munge(names).each { |n| @entered[n] << block }
+      end
+
+      def entering *names, &block
+        munge(names).each { |n| @entering[n] << block }
+      end
+
+      def fire instance, name, *args
+        raise "No [#{name}] event." unless @events.include? name
+
+        src  = instance.state
+        dest = @events[name].dest src
+
+        unless dest
+          raise "Can't [#{name}] while [#{instance.state}]: #{instance}"
+        end
+
+        ctx = Context.new instance, name, src.to_sym, dest, args
+
+        ActiveRecord::Base.transaction do
+          ctx.trigger @entering
+
+          instance.state = ctx.dest.to_s
+          ctx.trigger @entered
+
+          instance.save!
+        end
+
+        ctx.trigger @persisted
+
+        instance
+      end
+
+      def on *names, &block
+        names.flatten.each { |n| @events[n].instance_eval(&block) }
+      end
+
+      def persisted *names, &block
+        munge(names).each { |n| @persisted[n] << block}
+      end
+
+      def state name
+        name = name.to_s
+
+        unless @model.respond_to? name
+          @model.scope name, @model.where(state: name)
+          @model.send(:define_method, "#{name}?") { name == state }      
+        end
+      end
+
+      private
+
+      def munge names
+        names.flatten!
+        names.empty? ? [ANY] : names
+      end
+    end
+  end
+end
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