Move versionary script here

When we emptied this script out of
https://github.com/coreos/fedora-coreos-releng-automation/ in [[1]],
I'm not sure why I decided to move it to cosa instead of this repo,
where it clearly belongs much better.

[1]: coreos/coreos-assembler#3113

versionary

@@ -0,0 +1,173 @@
+#!/usr/bin/python3 -u
+
+# This file originally lived in
+# https://github.com/coreos/fedora-coreos-releng-automation. See that repo for
+# archeological git research.
+
+'''
+    Implements the Fedora CoreOS versioning scheme as per:
+        https://github.com/coreos/fedora-coreos-tracker/issues/81
+        https://github.com/coreos/fedora-coreos-tracker/issues/211
+'''
+
+import argparse
+import json
+import os
+import re
+import subprocess
+import sys
+import time
+import yaml
+
+from datetime import datetime
+
+# streams which don't use lockfiles
+UNLOCKED_STREAMS = [
+    'rawhide',
+    'branched',
+    'bodhi-updates-testing',
+    'bodhi-updates',
+]
+
+# https://github.com/coreos/fedora-coreos-tracker/issues/211#issuecomment-543547587
+STREAM_TO_NUM = {
+    'next': 1,
+    'testing': 2,
+    'stable': 3,
+    'next-devel': 10,
+    'testing-devel': 20,
+    'rawhide': 91,
+    'branched': 92,
+    'bodhi-updates-testing': 93,
+    'bodhi-updates': 94,
+}
+
+
+def main():
+    args = parse_args()
+    if args.workdir is not None:
+        os.chdir(args.workdir)
+    assert os.path.isdir('builds'), 'Missing builds/ dir'
+
+    manifest = get_flattened_manifest()
+    x, y, z = (get_x(manifest), get_y(manifest), get_z(manifest))
+    n = get_next_iteration(x, y, z)
+    new_version = f'{x}.{y}.{z}.{n}'
+
+    # sanity check the new version by trying to re-parse it
+    assert parse_version(new_version) is not None
+    print(new_version)
+
+
+def parse_args():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--workdir', help="path to cosa workdir")
+    return parser.parse_args()
+
+
+def get_x(manifest):
+    """
+        X is the Fedora release version on which we're based.
+    """
+    releasever = manifest['releasever']
+    eprint(f"x: {releasever} (from manifest)")
+    return int(releasever)
+
+
+def get_y(manifest):
+    """
+        Y is the base snapshot date in YYYYMMDD format of Fedora. We derive
+        this using the timestamp in the base lockfile.
+    """
+
+    stream = manifest['add-commit-metadata']['fedora-coreos.stream']
+
+    # XXX: should sanity check that the lockfiles for all the basearches have
+    # matching timestamps
+    exts = ['json', 'yaml']
+    for ext in exts:
+        try:
+            with open(f"src/config/manifest-lock.x86_64.{ext}") as f:
+                lockfile = yaml.safe_load(f)
+                generated = lockfile.get('metadata', {}).get('generated')
+                if not generated:
+                    raise Exception("Missing 'metadata.generated' key "
+                                    f"from {lockfile}")
+                dt = datetime.strptime(generated, '%Y-%m-%dT%H:%M:%SZ')
+                assert stream not in UNLOCKED_STREAMS
+                msg_src = "from lockfile"
+                break
+        except FileNotFoundError:
+            continue
+    else:
+        # must be an unlocked stream
+        assert stream in UNLOCKED_STREAMS
+        msg_src = "unlocked stream"
+        dt = datetime.now()
+
+    ymd = dt.strftime('%Y%m%d')
+    eprint(f"y: {ymd} ({msg_src})")
+    return int(ymd)
+
+
+def get_z(manifest):
+    """
+        Z is the stream indicator.
+    """
+    stream = manifest['add-commit-metadata']['fedora-coreos.stream']
+    assert stream in STREAM_TO_NUM, f"Unknown stream: {stream}"
+    mapped = STREAM_TO_NUM[stream]
+    eprint(f"z: {mapped} (mapped from stream {stream})")
+    return mapped
+
+
+def get_next_iteration(x, y, z):
+    try:
+        with open('builds/builds.json') as f:
+            builds = json.load(f)
+    except FileNotFoundError:
+        builds = {'builds': []}
+
+    if len(builds['builds']) == 0:
+        eprint("n: 0 (no previous builds)")
+        return 0
+
+    last_buildid = builds['builds'][0]['id']
+    last_version = parse_version(last_buildid)
+    if not last_version:
+        eprint(f"n: 0 (previous version {last_buildid} does not match scheme)")
+        return 0
+
+    if (x, y, z) != last_version[:3]:
+        eprint(f"n: 0 (previous version {last_buildid} x.y.z does not match)")
+        return 0
+
+    n = last_version[3] + 1
+    eprint(f"n: {n} (incremented from previous version {last_buildid})")
+    return n
+
+
+def get_flattened_manifest():
+    return yaml.safe_load(
+        subprocess.check_output(['rpm-ostree', 'compose', 'tree',
+                                 '--print-only', 'src/config/manifest.yaml']))
+
+
+def parse_version(version):
+    m = re.match(r'^([0-9]{2})\.([0-9]{8})\.([0-9]+)\.([0-9]+)$', version)
+    if m is None:
+        return None
+    # sanity-check date
+    try:
+        time.strptime(m.group(2), '%Y%m%d')
+    except ValueError:
+        return None
+    return tuple(map(int, m.groups()))
+
+
+def eprint(*args):
+    print(*args, file=sys.stderr)
+
+
+if __name__ == "__main__":
+    sys.exit(main())