#
#--
# Copyright (c) 2007-2008, John Mettraux, OpenWFE.org
# All rights reserved.
# 
# Redistribution and use in source and binary forms, with or without 
# modification, are permitted provided that the following conditions are met:
# 
# . Redistributions of source code must retain the above copyright notice, this
#   list of conditions and the following disclaimer.  
# 
# . Redistributions in binary form must reproduce the above copyright notice, 
#   this list of conditions and the following disclaimer in the documentation 
#   and/or other materials provided with the distribution.
# 
# . Neither the name of the "OpenWFE" nor the names of its contributors may be
#   used to endorse or promote products derived from this software without
#   specific prior written permission.
# 
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
# POSSIBILITY OF SUCH DAMAGE.
#++
#

#
# "made in Japan"
#
# John Mettraux at openwfe.org
#

require 'openwfe/expressions/condition'


module OpenWFE

    #
    # Some constants shared by 'cursor', 'loop', 'iterator' and
    # the CommandExpression.
    #
    module CommandConstants

        protected

            A_COMMAND_FIELD = "command-field"
            F_COMMAND = "__cursor_command__"
            A_DISALLOW = "disallow"

            C_BACK = "back"
            C_SKIP = "skip"
            C_BREAK = "break"
            C_CANCEL = "cancel"
            C_REWIND = "rewind"
            C_CONTINUE = "continue"
            C_JUMP = "jump"

            A_STEP = "step"
    end

    #
    # A mixin shared by 'iterator' and 'cursor' ('loop'), simply
    # provides the methods for looking up the "command" (break, skip, 
    # rewind, ...) from the workitem and the process.
    #
    module CommandMixin
        include CommandConstants

        protected

            def determine_command_and_step (workitem)

                command_field = lookup_command_field workitem

                command, step = lookup_command command_field, workitem

                disallow_list = lookup_disallow workitem

                command = nil \
                    if disallow_list and disallow_list.include?(command)

                workitem.attributes.delete(command_field)

                [ command, step ]
            end

        private

            #
            # Looks up the value in the command field.
            #
            def lookup_command_field (workitem)

                lookup_attribute(
                    A_COMMAND_FIELD, workitem, :default => F_COMMAND)
            end

            #
            # Returns the command and the step
            #
            def lookup_command (command_field, workitem)

                command = workitem.attributes[command_field]

                return [ nil, 1 ] unless command
                    #
                    # this corresponds to the "just one step forward" default

                command, step = command.strip.split

                step = if step
                    step.to_i
                else
                    1
                end

                step = -step if command == C_BACK

                [ command, step ]
            end

            #
            # Fetches the value of the 'disallow' cursor attribute.
            #
            def lookup_disallow (workitem)

                lookup_array_attribute A_DISALLOW, workitem
            end
    end

    #
    # This class implements the following expressions :  back, break,
    # cancel, continue, jump, rewind, skip.
    #
    # They are generally used inside of a 'cursor' (CursorExpression) or 
    # a 'loop' (LoopExpression), they can be used outside, but their result
    # (the value of the field '\_\_cursor_command__' will be used as soon as the
    # flow enters a cursor or a loop).
    #
    # In fact, this expression is only a nice wrapper that sets the
    # value of the field "\_\_cursor_command__" to its name ('back' for example)
    # plus to the 'step' attribute value.
    #
    # For example <skip step="3"/> simply sets the value of the field 
    # '\_\_cursor_command__' to 'skip 3'.
    #
    # (The field \_\_cursor_command__ is, by default, read and 
    # obeyed by the 'cursor' expression).
    #
    # With Ruby process definitions, you can directly write :
    #
    #     skip 2
    #     jump "0"
    #
    # instead of 
    #
    #     skip :step => "2"
    #     jump :step => "0"
    #
    # Likewise, in an XML process definition, you can write
    #
    #     <skip>2</skip>
    #
    # although that might still look lighter (it's longer though) :
    #
    #     <skip step="2"/>
    #
    #
    # About the command themselves :
    #
    # * back : will go back from the number of given steps, 1 by default
    # * break : will exit the cursor (or the loop)
    # * cancel : an alias for 'break'
    # * continue : will exit the cursor, if in a loop, will get back at step 0
    # * jump : will move the cursor (or loop) to an absolute given position (count starts at 0)
    # * rewind : an alias for continue
    # * skip : skips the given number of steps
    #
    #
    # All those command support an 'if' attribute to restrict their execution :
    #
    #     cursor do
    #         go_to_shop
    #         check_prices
    #         _break :if => "${price} > ${f:current_cash}"
    #         buy_stuff
    #     end
    #
    # The 'rif' attribute may be used instead of the 'if' attribute. Its value
    # is some ruby code that, when evaluating to true will let the command
    # be executed.
    #
    #     _skip 2, :rif => "workitem.customers.size % 2 == 0"
    #         #
    #         # skips if the nb of customers is pair
    #
    # Note that the 'rif' attribute will work only if the 
    # <tt>:ruby_eval_allowed</tt> parameter is set to true in the engine's
    # application context.
    #
    #     engine.application_context[:ruby_eval_allowed] = true
    #
    class CursorCommandExpression < FlowExpression
        include CommandConstants
        include ConditionMixin

        names :back, :skip, :continue, :break, :cancel, :rewind, :jump

        def apply (workitem)

            conditional = eval_condition(:if, workitem, :unless)
                #
                # for example : <break if="${approved} == true"/>

            if conditional == nil or conditional

                command = @fei.expression_name

                step = lookup_attribute(A_STEP, workitem)
                step = fetch_text_content(workitem) unless step
                step = 1 unless step
                step = Integer(step)

                command = "#{command} #{step}" #if step != 1

                workitem.attributes[F_COMMAND] = command
            end

            reply_to_parent workitem
        end
    end

end