#!/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)
            todo = [(b, new)]
            if new > 1:
                todo.insert(0, (a, old))
            for lines, version in todo:
                if versions[version]['attrs']['visible'] != 'true':
                    continue
                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].get('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()