caches: Move cache cleaning helper tools under scripts/lib.

This helps keep the root of scripts/ uncluttered.

scripts/lib/clean-venv-cache

@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+import argparse
+import os
+import sys
+
+if False:
+    from typing import Set, Text
+
+ZULIP_PATH = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+sys.path.append(ZULIP_PATH)
+from scripts.lib.hash_reqs import expand_reqs, hash_deps
+from scripts.lib.zulip_tools import GENERIC_CACHE_SCRIPT_PARSER, \
+    get_caches_to_be_purged, get_environment, get_recent_deployments, \
+    purge_unused_caches
+
+ENV = get_environment()
+VENV_CACHE_DIR = '/srv/zulip-venv-cache'
+if ENV == "travis":
+    VENV_CACHE_DIR = os.path.join(os.environ["HOME"], "zulip-venv-cache")
+
+def parse_args():
+    # type: () -> argparse.Namespace
+    parser = argparse.ArgumentParser(description="This script cleans unused zulip venv caches.",
+                                     parents=[GENERIC_CACHE_SCRIPT_PARSER, ])
+    args = parser.parse_args()
+    return args
+
+def get_caches_in_use(threshold_days):
+    # type: (int) -> Set[Text]
+    setups_to_check = set([ZULIP_PATH, ])
+    caches_in_use = set()
+
+    if ENV == "prod":
+        setups_to_check |= get_recent_deployments(threshold_days)
+    if ENV == "dev":
+        CACHE_SYMLINK = os.path.join(os.path.dirname(ZULIP_PATH), "zulip-py3-venv")
+        CURRENT_CACHE = os.path.dirname(os.path.realpath(CACHE_SYMLINK))
+        caches_in_use.add(CURRENT_CACHE)
+
+    for path in setups_to_check:
+        for filename in os.listdir(os.path.join(path, "requirements")):
+            requirements_file = os.path.join(path, "requirements", filename)
+            deps = expand_reqs(requirements_file)
+            hash_val = hash_deps(deps)
+            caches_in_use.add(os.path.join(VENV_CACHE_DIR, hash_val))
+
+    return caches_in_use
+
+def main():
+    # type: () -> None
+    args = parse_args()
+    caches_in_use = get_caches_in_use(args.threshold_days)
+    purge_unused_caches(VENV_CACHE_DIR, caches_in_use, args.threshold_days, args.dry_run, "venv")
+
+if __name__ == "__main__":
+    main()