--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/.hgignore	Fri Nov 10 11:52:37 2017 +0800
@@ -0,0 +1,3 @@
+syntax: glob
+
+*.pyc

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/diff.py	Fri Nov 10 11:52:37 2017 +0800
@@ -0,0 +1,141 @@
+#!/usr/bin/env python3
+from argparse import ArgumentParser
+from difflib import unified_diff
+from subprocess import run
+from sys import stderr
+from tempfile import NamedTemporaryFile
+from time import sleep
+from urllib.request import urlopen
+from xml.etree import ElementTree as ET
+
+
+API = 'https://api.openstreetmap.org/api/0.6'
+
+
+def clear_progress():
+    stderr.write('\n')
+    stderr.flush()
+
+
+def fetch_xml(url, what, n, total, delay=200, spins=r'/-\|'):
+    sleep(delay / 1000)
+    stderr.write('\r{} {} {} out of {}'.format(spins[n % len(spins)], what, n, total))
+    stderr.flush()
+    with urlopen(url) as response:
+        tree = ET.parse(response)
+    return tree.getroot()
+
+
+def parse_item_xml(kind, el):
+    data = {
+        'attrs': el.attrib,
+        'tags': {
+            tag.get('k'): tag.get('v')
+            for tag in el.findall('tag')
+        }
+    }
+    if kind == 'way':
+        data['refs'] = [
+            (ref.tag, ref.get('ref'), None)
+            for ref in el.findall('*[@ref]')
+        ]
+    elif kind == 'relation':
+        data['refs'] = [
+            (member.get('type'), member.get('ref'), member.get('role'))
+            for member in el.findall('member')
+        ]
+    return data
+
+
+def bootstrap(csid):
+    items = {'node': {}, 'way': {}, 'relation': {}}
+
+    # changeset metadata mostly
+    xml = fetch_xml('{}/changeset/{}'.format(API, csid), 'changeset data', 1, 2, delay=0)
+    changeset = {
+        'attrs': xml.find('changeset').attrib,
+        'tags': {
+            tag.get('k'): tag.get('v')
+            for tag in xml.find('changeset').findall('tag')
+        }
+    }
+
+    # current versions of nodes, ways, relations
+    xml = fetch_xml('{}/changeset/{}/download'.format(API, csid), 'changeset data', 2, 2)
+    for node in xml:
+        if node.tag not in ('create', 'modify', 'delete'):
+            continue
+        el = node[0]
+        if el.tag not in ('node', 'way', 'relation'):
+            continue
+        id = int(el.get('id'))
+        version = int(el.get('version'))
+        items[el.tag][id] = {
+            version: parse_item_xml(el.tag, el)
+        }
+
+    # fetch previous versions
+    for kind in ('node', 'way', 'relation'):
+        clear_progress()
+        total = len(items[kind])
+        for n, id in enumerate(items[kind], 1):
+            version = min(items[kind][id])
+            if version == 1:
+                continue
+            version -= 1
+            xml = fetch_xml('{}/{}/{}/{}'.format(API, kind, id, version), kind + 's', n, total)
+            items[kind][id][version] = parse_item_xml(kind, xml.find(kind))
+
+    return changeset, items
+
+
+def level0lify(changeset, items, refmap={'node': 'nd', 'way': 'wy'}):
+    a = []
+    b = []
+    a.append('# previous changeset is most likely unrelated')
+    b.append('changeset {}'.format(changeset['attrs']['id']))
+    b += ['  {} = {}'.format(k, v) for k, v in sorted(changeset['tags'].items())]
+    for kind in ('relation', 'way', 'node'):
+        for id in sorted(items[kind]):
+            versions = items[kind][id]
+            old = min(versions)
+            new = max(versions)
+            for lines, version in ((a, old), (b, new)):
+                lines.append('')
+                lines.append('{} {}'.format(kind, id))
+                lines += [
+                    '  {} = {}'.format(k, v)
+                    for k, v in sorted(versions[version]['tags'].items())
+                ]
+                lines += [
+                    '  {} {}{}'.format(refmap.get(kind, kind), id, ' ' + role if role is not None else '')
+                    for kind, id, role in versions[version]['refs']
+                ]
+    return a, b
+
+
+def main():
+    parser = ArgumentParser()
+    parser.add_argument('changeset', type=int, help='changeset id')
+    group = parser.add_mutually_exclusive_group()
+    group.add_argument('-U', '--unified', type=int, help='lines of context')
+    group.add_argument('-t', '--tool', help='external tool to use for diffing')
+    args = parser.parse_args()
+
+    changeset, items = bootstrap(args.changeset)
+    a, b = level0lify(changeset, items)
+    clear_progress()
+    if args.tool is None:
+        context = args.unified if args.unified is not None else 3
+        diff = unified_diff(a, b, n=context, lineterm='')
+        print('\n'.join(diff))
+    else:
+        with NamedTemporaryFile() as afile, NamedTemporaryFile() as bfile:
+            for fd, lines in ((afile, a), (bfile, b)):
+                fd.write('\n'.join(lines).encode('utf-8'))
+                fd.flush()
+            run([args.tool, afile.name, bfile.name])
+
+
+if __name__ == '__main__':
+    main()