Write out an ERDDAP `datasets.xml` after comparing and old and new file for dataset removals.

difference.py

#! /usr/bin/env python
import os
import argparse

from lxml import etree


def main(oldxml, newxml, outfile):

    oldtree = None
    if os.path.isfile(oldxml):
        oldtree = etree.parse(oldxml)

    newtree = None
    if os.path.isfile(newxml):
        newtree = etree.parse(newxml)

    if oldtree and newtree:
        # Find removed datasets
        datasetids = etree.XPath(
            "//erddapDatasets/dataset/@datasetID",
            smart_strings=False
        )

        oldids = set(list(datasetids(oldtree)))
        newids = set(list(datasetids(newtree)))
        removedids = list(oldids.difference(newids))

        find_dataset = etree.XPath("//erddapDatasets/dataset[@datasetID=$name]")
        for r in removedids:
            # **** NOTE ****
            # This won't handle a dataset that was marked as active=false
            # and then came back into the picture. It won't remove active=false
            # and the datasets will be in a state of purgatory. This shouldn't
            # happen often, if ever.
            dnode = find_dataset(oldtree, name=r)[0]
            if dnode.get('active') == 'false':
                # Don't do anything, it's ready to be removed from the datasets.xml
                pass
            else:
                # Deactivate the dataset
                dnode.set('active', 'false')
                ds = newtree.getroot()
                ds.append(dnode)

    if not oldtree and newtree:
        print("No existing datasets.xml so using the newly generated one")

    if newtree:
        with open(outfile, 'wt') as f:
            f.write(etree.tostring(newtree, encoding='ISO-8859-1', pretty_print=True, xml_declaration=True).decode('iso-8859-1'))
            f.write('\n')
    else:
        print("Not doing anything. No new datasets.xml file.")


if __name__ == "__main__":

    parser = argparse.ArgumentParser()

    parser.add_argument('oldxml',
                        help="Old datasets.xml file",
                        nargs='?')
    parser.add_argument('newxml',
                        help="New datasets.xml file",
                        nargs='?')
    parser.add_argument('outfile',
                        help="File to write the final datasets.xml",
                        nargs='?')
    args = parser.parse_args()

    main(args.oldxml, args.newxml, args.outfile)