# This function takes a flatwire HL7 message as its argument
# and returns the same HL7 message. Any group of segments that
# starts with IN is sorted into alphabetical order.
# So if the HL7 message had a group of IN1 and IN2 segments
# like this:
#   IN1|3|Blah
#   IN2|3|Ditch
#   IN1|2|Blah
#   IN1|1|Smith
#   IN2|2|Ditch
#   IN2|1|Ditch
# Then the expected order of the segments would be:
#   IN1|1|Smith
#   IN1|2|Blah
#   IN1|3|Blah
#   IN2|1|Ditch
#   IN2|2|Ditch
#   IN2|3|Ditch
# There are some boundary conditions that this routine will not handle well.
#    1. If a message has several groups of IN* segments separated by other types of segments,
#       only the first group in IN* segments will be sorted.
#    2. The segments are sorted in alphabetical order, which means that if field 1 of the INI
#       segment goes into 2 characters, one gets some unexpected results. For example,
#   IN1|4|blah
#   IN1|30|blah
#   IN1|5|delta
# gets sorted into
#   IN1|30|blah
#   IN1|4|blah
#   IN1|5|delta
# So make sure that the message data you have does not generate sequences like the above.

def sort_ini(value):
    # We start by breaking the message into a Python list object of segments
    # See http://www.interfaceware.com/manual/python_lists.html
    segment_list = value.split('\r')

    # Now we're going to create three empty lists - the idea is to sort the segments
    # into a list of segments before the IN* segments, the list of IN* segments and
    # a list of IN* segments afterwards.
    before_ini = []
    ini_list = []
    after_ini = []

    reached_ini = 0 # i.e. false - we'll flip this flag when we reach the IN* segments

    # We iterate through list of segments, put the ones
    # before the IN* segments into the before_ini list,
    # the IN* segments into ini_list
    # and the ones afterwards in after_ini
    # See http://www.interfaceware.com/manual/python_string_indexing.html
    # to understand the syntax used here for python string manipulation  

    for segment in segment_list:
        if segment[0:2] == "IN":
           ini_list.append(segment)
           reached_ini = 1
        elif reached_ini:
           after_ini.append(segment)
        else:
           before_ini.append(segment)

    # Now we use the python sort method to sort the list of INI segments
    # It does it alphabetically
    ini_list.sort()

    # Then concatenate the lists together again
    complete_list = before_ini + ini_list + after_ini

    # This final command joins the segment strings together again, putting the \r
    # segment delimiters back in.
    return "\r".join(complete_list)

# This is how to call our INI swap function
# value should contain a complete HL7 message
value = sort_ini(value)