Introduce hold-differentiated states

States can now receive parameters from the holds placed on them out of a
specific set of parameters marked for this kind of retrieval, /and/ multiple
states can be differentiated based on this mechanism.

1 files changed, 41 insertions, 8 deletions

diff --git a/state.rb b/state.rb
index d3782f9..2a52b19 100644
--- a/state.rb
+++ b/state.rb
@@ -21,6 +21,10 @@ module UpState
 # Occurs when the state machine becomes inconsistent
 class ConsistencyFault < StandardError; end
 
+# Occurs when something tries to bring up a state without filling
+# out its parameters
+class AmbiguousRequest < StandardError; end
+
 ENABLE_TRACE = false
 
 def trace(*args)
@@ -37,15 +41,17 @@ class State
 	attr :holds  # Holds that are had on this state
 	attr :status # Are we up? Down? Getting there?
 	class << self
-		attr :depends			 # What states does this state depend on?
-		attr :caused_by		 # What events can cause this state?
-		attr :rising_edge	 # What do we do as we're coming up?
-		attr :falling_edge # What do we do as we're going down?
+		attr :depends			  # What states does this state depend on?
+		attr :caused_by		  # What events can cause this state?
+		attr :rising_edge	  # What do we do as we're coming up?
+		attr :falling_edge  # What do we do as we're going down?
+		attr :hold_provides # What params should come from this state's holder?
 	protected
 		attr_writer :depends
 		attr_writer :caused_by
 		attr_writer :rising_edge
 		attr_writer :falling_edge
+		attr_writer :hold_provides
 	end
 
 	@@states = Set.new      # Set of activatable states
@@ -58,6 +64,7 @@ class State
 		@holds = Set.new
 		@deps = deps.to_set
 		@status = :down
+		@hold_params = {}
 
 		return if @@states.include? self
 		@@states.add self
@@ -121,12 +128,36 @@ class State
 		hold = Hold::User.new(params) if hold == :user
 		hold = Hold::System.new(params) if hold == :system
 		raise TypeError unless hold.is_a? Hold
+		if @status == :down and self.class.hold_provides.size > 0
+			return self.fork(hold)
+		end
 		trace "#{self} being held with #{hold}"
 		@holds.add hold
-		rise if @holds.size == 1
+		rise if @status == :down
 		self
 	end
 
+	# Duplicate this class and bring the duplicate up with the given hold attached
+	def fork(hold)
+		new_one = self.clone
+		new_one.instance_eval do
+			@holds = Set.new [hold]
+			@hold_params = {}
+			self.class.hold_provides.each do |x|
+				hold.params[x] or raise AmbiguousRequest, "#{x} undefined"
+				@hold_params[x] = hold.params[x]
+			end
+		end
+		@@states.each do |state|
+			next unless state == new_one
+			state.hold(hold)
+			return state
+		end
+		@@states.add new_one
+		new_one.send :rise
+		new_one
+	end
+
 	# Release a hold on this state. Arguments are the same as for +hold+.
 	def release(hold, params = {})
 		hold = Hold::Dep.new(hold) if hold.is_a? State
@@ -146,8 +177,7 @@ class State
 
 	# Parameters to this state
 	def params
-		@deps.map{ |x| x.params }.inject({}){ |x,y| x.merge y }.merge \
-			@holds.map{ |x| x.params }.inject({}){ |x,y| x.merge y }
+		@deps.map{ |x| x.params }.inject({}){ |x,y| x.merge y }.merge @hold_params
 	end
 
 	# Set this state to untrue without running any falling edge code
@@ -162,6 +192,7 @@ class State
 			trace "#{self} becomes defunct"
 		end
 		@deps.each{ |x| x.state.release(self) }
+		@hold_params = {}
 		@status = :down
 		State.gc
 		State.depsolve_all
@@ -198,7 +229,7 @@ class State
 	# Create a new type of state. +name+ is capitalized and postfixed with "State"
 	# to create the new state class name. +depends+ is a series of Dependency
 	# Objects. This method is not defined in subclasses of State.
-	def State.new_type(name, caused_by, depends)
+	def State.new_type(name, caused_by, depends, hold_provides = [])
 		name = name.capitalize + "State"
 		raise NameError, "State already exists" if self.const_defined? name
 		newtype = const_set(name, Class.new(State))
@@ -206,6 +237,7 @@ class State
 		newtype.caused_by = caused_by
 		newtype.rising_edge = Proc.new{}
 		newtype.falling_edge = Proc.new{}
+		newtype.hold_provides = hold_provides
 		newtype.instance_eval do
 			undef :new_type, :process_event, :gc, :depsolve_all
 		end
@@ -230,6 +262,7 @@ class State
 	# Remove inactive states whose deps are no longer satisfied. This method is
 	# not defined in subclasses of State.
 	def State.gc
+		@@states = @@states.to_a.to_set # Mutability + identity = pain. Semper λ
 		@@states.each{ |x| x.check_deps }
 		nil
 	end