[NO TESTS] WIP

projects/archlinux/rollback.py

@@ -0,0 +1,94 @@
+import os
+import re
+import sys
+
+
+def main(opts, args):
+    """Usage: python rollback.py date
+
+    Parse /var/log/pacman.log, enumerating package transactions since the
+    specified date and building a plan for restoring the state of your system to
+    what it was at the specified date.
+
+    Assumes:
+    - /var/log/pacman.log has not been truncated
+
+    - /var/cache/pacman/pkg has not been flushed and still contains all required
+      packages
+
+    - The above paths are Arch default and have not been customized
+
+    - That it is not necessary to remove any "installed" packages
+
+    Note: no attempt is made to inspect the dependency graph of packages to be
+    downgraded to detect when a package is already transitively listed for
+    downgrading. This can create some annoying errors where eg. systemd will be
+    downgraded, meaning libsystemd will also be downgraded, but pacman considers
+    explicitly listing the downgrade of libsystemd when it will already be
+    transitively downgraded an error.
+
+    """
+
+    date, = args
+
+    print("Attempting to roll back package state to that of {0}...\n"
+          .format(date),
+          file=sys.stderr)
+
+    # These patterns can't be collapsed because we want to select different
+    # version identifying strings depending on which case we're in. Not ideal,
+    # but it works.
+
+    # Ex. [2017-04-01 09:51] [ALPM] upgraded filesystem (2016.12-2 -> 2017.03-2)
+    upgraded_pattern = re.compile(
+        ".*? upgraded (?P<name>\w+) \((?P<from>[^ ]+) -> (?P<to>[^\)]+)\)")
+
+    # Ex: [2018-02-23 21:18] [ALPM] downgraded emacs (25.3-3 -> 25.3-2)
+    downgraded_pattern = re.compile(
+        ".*? downgraded (?P<name>\w+) \((?P<to>[^ ]+) -> (?P<from>[^\)]+)\)")
+
+    # Ex: [2017-03-31 07:05] [ALPM] removed gdm (3.22.3-1)
+    removed_pattern = re.compile(
+        ".*? removed (?P<name>\w+) \((?P<from>[^ ]+)\)")
+
+    checkpoint = {}
+    flag = False
+
+    with open("/var/log/pacman.log") as logfile:
+        for line in logfile:
+            if date in line:
+                flag = True
+            elif not flag:
+                continue
+
+            match = re.match(upgraded_pattern, line)\
+                or re.match(downgraded_pattern, line)\
+                or re.match(removed_pattern, line)
+
+            if match:
+                package = match.group("name")
+                from_rev = match.group("from")
+                if package not in checkpoint:
+                    checkpoint[package] = from_rev
+                continue
+
+    print("Checkpoint state:")
+    for k in checkpoint.keys():
+        print("{0} -> {1}".format(k, checkpoint[k]), file=sys.stderr)
+
+    pkgcache = "/var/cache/pacman/pkg"
+    pkgs = os.listdir(pkgcache)
+    pkgnames = ["{0}-{1}".format(k, v) for k, v in checkpoint.items()]
+
+    selected_pkgs = set([os.path.join(pkgcache, p)
+                         for n in pkgnames
+                         for p in pkgs
+                         if n in p])
+
+    print("Suggested incantation:\n", file=sys.stderr)
+    print("sudo pacman --noconfirm -U {}"
+          .format("\\\n  ".join(selected_pkgs)))
+
+
+if __name__ == "__main__":
+  main(None, sys.argv[1:])