#
#--
# 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 
# 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/wtemplate'
require 'openwfe/expressions/flowexpression'
require 'openwfe/expressions/fe_command'


module OpenWFE

    #
    # The 'iterator' expression can be used like that for example :
    #
    #     <iterator
    #         on-value="alice, bob, charles"
    #         to-variable="user-name"
    #     >
    #         <set 
    #             field="${user-name} comment" 
    #             value="(please fill this field)"
    #         />
    #     </iterator>
    #
    # Within the iteration, the workitem field "\_\_ic__" contains the number
    # of elements in the iteration and the field "\_\_ip__" the index of the
    # current iteration.
    #
    # The 'iterator' expression understands the same cursor commands as the
    # CursorExpression. One can thus exit an iterator or skip steps in it.
    #
    #     iterator :on_value => "alice, bob, charles, doug", to_variable => "v" do
    #         sequence do
    #             participant :variable_ref => "v"
    #             skip 1, :if => "${f:reply} == 'skip next'"
    #         end
    #     end
    #
    class IteratorExpression < WithTemplateExpression
        include CommandMixin

        names :iterator

        #
        # an Iterator instance that holds the list of values being iterated
        # upon.
        #
        attr_accessor :iterator

        def apply (workitem)

            if @children.length < 1
                reply_to_parent workitem
                return
            end

            @iterator = Iterator.new(self, workitem)

            if @iterator.size < 1
                reply_to_parent workitem
                return
            end

            reply workitem
        end

        def reply (workitem)

            command, step = determine_command_and_step workitem

            vars = if not command

                @iterator.next workitem

            elsif command == C_BREAK or command == C_CANCEL

                nil

            elsif command == C_REWIND or command == C_CONTINUE

                @iterator.rewind workitem

            elsif command.match "^#{C_JUMP}"

                @iterator.jump workitem, step

            else # C_SKIP or C_BACK

                @iterator.skip workitem, step
            end

            unless vars
                reply_to_parent workitem
                return
            end

            store_itself

            get_expression_pool.launch_template(
                self, @iterator.index, @children[0], workitem, vars)
        end
    end

    #
    # Iterator instances keep track of the position of an iteration.
    # This class is meant to be used both by <iterator> and 
    # <concurrent-iterator>.
    #
    class Iterator

        ITERATOR_COUNT = "__ic__"
        ITERATOR_POSITION = "__ip__"

        attr_accessor :iteration_index
        attr_accessor :iteration_list
        attr_accessor :to_field
        attr_accessor :to_variable
        attr_accessor :value_separator

        #
        # Builds a new iterator, serving a given iterator_expression. 
        # The second parameter is the workitem (as applied to the iterator
        # expression).
        #
        def initialize (iterator_expression, workitem)

            @to_field = iterator_expression\
                .lookup_attribute(:to_field, workitem)
            @to_variable = iterator_expression\
                .lookup_attribute(:to_variable, workitem)

            @value_separator = iterator_expression\
                .lookup_attribute(:value_separator, workitem)

            @value_separator = /,\s*/ unless @value_separator

            @iteration_index = 0

            raw_list = iterator_expression.lookup_vf_attribute(
                workitem, :value, :on)

            @iteration_list = extract_iteration_list(raw_list)

            workitem.attributes[ITERATOR_COUNT] = @iteration_list.length
        end

        #
        # Has the iteration a next element ?
        #
        def has_next?

            @iteration_index < @iteration_list.size
        end

        #
        # Returns the size of this iterator, or rather, the size of the
        # underlying iteration list.
        #
        def size

            @iteration_list.size
        end

        #
        # Prepares the iterator expression and the workitem for the next 
        # iteration.
        #
        def next (workitem)

            position_at workitem, @iteration_index
        end

        #
        # Positions the iterator back at position 0.
        #
        def rewind (workitem)

            position_at workitem, 0
        end

        #
        # Jumps to a given position in the iterator
        #
        def jump (workitem, index)

            index = if index < 0
                0
            elsif index >= @iteration_list.size
                @iteration_list.size
            else
                index
            end

            position_at workitem, index
        end

        #
        # Jumps a certain number of positions in the iterator.
        #
        def skip (workitem, offset)

            jump workitem, @iteration_index + offset
        end

        #
        # The current index (whereas @iteration_index already points to
        # the next element).
        #
        def index

            @iteration_index - 1
        end

        protected

            #
            # Positions the iterator absolutely.
            #
            def position_at (workitem, position)

                result = {}

                value = @iteration_list[position]

                return nil unless value

                if @to_field
                    workitem.attributes[@to_field] = value
                else
                    result[@to_variable] = value
                end

                workitem.attributes[ITERATOR_POSITION] = position
                result[ITERATOR_POSITION] = position

                @iteration_index = position + 1

                result
            end

            #
            # Extracts the iteration list from any value.
            #
            def extract_iteration_list (raw_list)

                if is_suitable_list?(raw_list)
                    raw_list
                else
                    extract_list_from_string(raw_list.to_s)
                end
            end

            #
            # Returns true if the given instance can be directly
            # used as a list.
            #
            def is_suitable_list? (instance)

                (not instance.is_a?(String)) and \
                instance.respond_to? :[] and \
                instance.respond_to? :length
            end

            #
            # Extracts the list from the string (comma separated list
            # usually).
            #
            def extract_list_from_string (s)

                s.split(@value_separator)
            end
    end

end