#!/usr/bin/ruby

require 'AbstractConstraint'
require 'extensions'

module ConstraintSolver
    # Represents a one-of-equals constraint.
    class OneOfEqualsConstraint < AbstractConstraint
	attr_reader :variables, :value, :violationCost
	# Initialises a new one-of-equals constraint.
	# The arguments are the list of variables involved in the constraint and
	# the value at least one of the variables should be equal to.
	# Optionally, a cost for violating the constraint can be specified.
	def initialize(variables, value, violationCost=1)
	    if variables.empty?
		raise ArgumentError, "List of variables must not be empty!"
	    end
	    @variables = variables
	    @value = value
	    @violationCost = violationCost
	end

	def holds?
	    if not allAssigned? or not @variables.find { |var| var.value == @value }.nil?
		return true
	    else
		return false
	    end
	end

	def allAssigned?
	    @variables.each { |var|
		return false if not var.assigned?
	    }
	    return true
	end

	def include?(variable)
	    @variables.include?(variable)
	end

	def to_s
	    @variables.collect { |var| var.name }.join(" != ")
	end

	def to_s_full
	    @variables.collect { |var| var.to_s }.join(" != ")
	end

	def ==(constraint)
	    return false unless constraint.kind_of?(OneOfEqualsConstraint)
	    (@variables == constraint.variables) and (@value == constraint.value) and
		(@violationCost == constraint.violationCost)
	end

	def each
	    @variables.each { |var|
		yield var
	    }
	end

	def revise
	    checks = 0
	    revisedVariables = []
	    wipeout = false
	    if @variables.find_all { |var| var.assigned? and not var.value == @value }.size == @variables.size - 1
		unassigned = @variables.find { |var| not var.assigned? }
		pruneList = unassigned.domain.values - [ @value ]
		if not pruneList.empty?
		    begin
			unassigned.domain.prune(pruneList)
		    rescue DomainWipeoutException
			wipeout = true
		    end
		    revisedVariables << unassigned
		end
	    end
	    return revisedVariables, checks, wipeout
	end
    end
end