gerrit: move the download-gerrit-topic.py script from internal

Change-Id: I6441d5250b261f11e873c88c6a73d7aaec188844

download-gerrit-topic.py

diff --git a/download-gerrit-topic.py b/download-gerrit-topic.py
new file mode 100755
index 0000000..52596a3
--- /dev/null
+++ b/download-gerrit-topic.py
@@ -0,0 +1,122 @@
+#!/usr/bin/env python3
+"""Download from gerrit all the changes of the specified topic. The new
+branches will be called TOPIC. If a project has multiple changes, they must
+all form a parent-child chain, and only the last child will be downloaded.
+"""
+
+import argparse
+import http
+import logging
+import subprocess
+import sys
+import tempfile
+
+from louhi.common import gerrit
+from louhi.common.utils import run
+
+logger = logging.getLogger()
+logger.setLevel(logging.INFO)
+
+
+def get_parser():
+    """Constract the command line parser."""
+    parser = argparse.ArgumentParser(description=__doc__)
+
+    parser.add_argument('-b',
+                        '--branch',
+                        type=str,
+                        help='branch name to use, instead of TOPIC.')
+
+    parser.add_argument('--force',
+                        action='store_true',
+                        help='delete the branch if it already exists.')
+
+    parser.add_argument(
+        '-s',
+        '--status',
+        type=str,
+        choices=[
+            'abandoned', 'closed', 'merged', 'new', 'pending', 'reviewed',
+            'open'
+        ],
+        default='open',
+        help='(default: open) limit to changes with matching status; '
+        'see also --no-status.')
+
+    parser.add_argument(
+        '--no-status',
+        dest="status",
+        action='store_const',
+        const=None,
+        help='don\'t limit to changes by status; see also --status.')
+
+    parser.add_argument('--repo-path',
+                        metavar='PATH',
+                        type=str,
+                        default='repo',
+                        help='(default: repo) path to the repo executable.')
+
+    parser.add_argument('topic', metavar='TOPIC')
+
+    return parser
+
+
+def main():
+    """The main function."""
+    args = get_parser().parse_args()
+
+    branch = args.branch if args.branch else args.topic
+
+    try:
+        git_cookie_file = run(['git', 'config', 'http.cookieFile'],
+                              verbose=False).read().rstrip()
+    except subprocess.CalledProcessError:
+        logging.error('The git option http.cookieFile is not set.')
+        return 1
+
+    cookies = http.cookiejar.MozillaCookieJar()
+    with tempfile.NamedTemporaryFile('w', encoding='ascii') as temp_file:
+        # NB: MozillaCookieJar requires the file to start with the
+        # following line, so we add it in a temp file.
+        temp_file.write('# Netscape HTTP Cookie File\n')
+        with open(git_cookie_file, 'r', encoding='ascii') as cookie_file:
+            temp_file.write(cookie_file.read())
+        temp_file.flush()
+        cookies.load(temp_file.name)
+
+    changes = gerrit.query_topic(args.topic,
+                                 args.status,
+                                 access_cookie=cookies)
+    if not changes:
+        logging.error('No changes to download.')
+        return 1
+
+    branch_exists = run([args.repo_path, 'forall'] + list(changes) + [
+        '--command', f'! git rev-parse --verify "{branch}" &>/dev/null '
+        '|| echo "$REPO_PROJECT"'
+    ],
+                        verbose=False).read().split('\n')[:-1]
+    if branch_exists:
+        if not args.force:
+            logging.error(
+                'The branch %s alread exists in %s (use --force to '
+                'overwrite it.)', branch, branch_exists)
+            return 1
+
+        logging.info('Deleting branch %s from %s', branch, branch_exists)
+        run([args.repo_path, 'forall'] + branch_exists + [
+            '--command',
+            f'if git rev-parse --verify "{branch}" &>/dev/null; then'
+            '  git checkout --detach HEAD;'
+            f'  git branch --delete "{branch}" --force;'
+            'fi'
+        ])
+
+    logging.info('Downloading changes: %s', dict(changes))
+    run([args.repo_path, 'download', f'--branch={branch}', '--verbose'] +
+        [str(part) for change in changes.items() for part in change])
+    return 0
+
+
+if __name__ == '__main__':
+    sys.exit(main())