#
#--
# Copyright (c) 2007, 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 
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# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
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#++
#
# $Id: definitions.rb 2725 2006-06-02 13:26:32Z jmettraux $
#

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

require 'openwfe/expressions/condition'
require 'openwfe/expressions/wtemplate'
require 'openwfe/expressions/flowexpression'


#
# 'cursor' and 'loop' expressions
#

module OpenWFE

    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"

    #
    # The 'cursor' is much like a sequence, but you can go
    # back and forth within it, as it reads the field '\_\_cursor_command__' (or
    # the field specified in the 'command-field' attribute) at each
    # transition (each time it's supposed to move from one child expression to
    # the next).
    #
    #     cursor do
    #         participant "alpha"
    #         skip :step => "2"
    #         participant "bravo"
    #         participant "charly"
    #         set :field => "__cursor_command__", value => "2"
    #         participant "delta"
    #         participant "echo"
    #         skip 2
    #         participant "fox"
    #         #
    #         # in that cursor example, only the participants alpha, charly and
    #         # echo will be handed a workitem
    #         # (notice the last 'skip' with its light syntax)
    #         #
    #     end
    #
    # As you can see, you can directly set the value of the field 
    # '\_\_cursor_command__' or use a CursorCommandExpression like 'skip' or
    # 'jump'.
    #
    class CursorExpression < WithTemplateExpression

        names :cursor

        attr_accessor \
            :loop_id,
            :current_child_id,
            :current_child_fei

        #
        # apply / reply

        def apply (workitem)

            @loop_id = 0

            @current_child_id = -1

            clean_children_list()

            reply(workitem)
        end

        def reply (workitem)

            if @children.length < 1
                #
                # well, currently, no infinite empty loop allowed
                #
                reply_to_parent(workitem)
                return
            end

            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)

            ldebug { "reply() command is '#{command} #{step}'" }

            if command == C_BREAK or command == C_CANCEL
                reply_to_parent workitem
                return
            end

            if command == C_REWIND or command == C_CONTINUE

                @current_child_id = 0

            elsif command and command.match "^#{C_JUMP}"

                @current_child_id = step
                @current_child_id = 0 if @current_child_id < 0

                @current_child_id = @children.length - 1 \
                    if @current_child_id >= @children.length

            else # C_SKIP or C_BACK

                @current_child_id = @current_child_id + step

                @current_child_id = 0 if @current_child_id < 0

                if @current_child_id >= @children.length
                    if not is_loop
                        reply_to_parent(workitem)
                        return
                    end
                    @loop_id += 1
                    @current_child_id = 0
                end
            end

            workitem.attributes.delete(command_field)

            @current_child_fei = nil

            store_itself()

            @current_child_fei = @children[@current_child_id]

            #
            # launch the next child as a template

            get_expression_pool.launch_template(
                self, @loop_id, @current_child_fei, workitem, nil)
        end

        #
        # takes care of cancelling the current child if necessary
        #
        def cancel
            get_expression_pool.cancel(@current_child_fei) \
                if @current_child_fei
            super
        end

        #
        # Returns false, the child class LoopExpression does return true.
        #
        def is_loop
            false
        end

        protected

            #
            # Makes sure that only flow expression are left in the cursor
            # children list (text and comment nodes get discarded).
            #
            def clean_children_list

                c = @children
                @children = []
                c.each do |child|
                    @children << child \
                        if child.kind_of?(OpenWFE::FlowExpressionId)
                end
            end

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

                lookup_attribute(A_COMMAND_FIELD, workitem, 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_comma_list_attribute(A_DISALLOW, workitem)
            end
    end

    #
    # The 'loop' expression is like 'cursor' but it doesn't exit until
    # it's broken (with 'break' or 'cancel').
    #
    class LoopExpression < CursorExpression

        names :loop

        def is_loop
            true
        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
    #
    class CursorCommandExpression < FlowExpression
        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