add build timestamp to avoid useless image builds

* skip build if image timestamp is newer than config file

runon/runon.py

@@ -10,6 +10,8 @@ import os
 import re
 import xdg.BaseDirectory
 import yaml
+import datetime
+import pytz
 import subprocess
 from pprint import pprint
 
@@ -33,6 +35,7 @@ def read_yaml(conf_file):
     try:
         with open(conf_file, 'r') as file:
             conf = yaml.safe_load(file)
+            conf['stamp'] = datetime.datetime.fromtimestamp(os.path.getmtime(conf_file), tz=pytz.UTC)
         return conf
     except yaml.YAMLError as e:
         print(f'ERROR: bad configuration file:')
@@ -62,6 +65,7 @@ def load_config(conf_file, osname):
         print(f"ERROR: cannot find configuration for distribution {osname}")
         sys.exit(1)
 
+    osconf['stamp'] = conf.get('stamp')
     osconf['osname'] = osname
     for k in [ 'dockerfile', 'packages', 'environment', 'binds' ]:
         if osconf.get(k):
@@ -83,6 +87,24 @@ def make_image_name(osname):
 
 
 def build_image(client, conf, update, verbose):
+    osname = conf.get('osname')
+    image_name = 'runon-{}'.format(osname)
+    tag = make_image_name(conf['osname'])
+    cache_dir = os.path.join(xdg.BaseDirectory.xdg_cache_home, 'runon')
+    cache_file = os.path.join(cache_dir, image_name)
+
+    if not update and os.path.exists(cache_file):
+        ts_image = datetime.datetime.fromtimestamp(os.path.getmtime(cache_file), tz=pytz.UTC)
+        ts_conf = conf.get('stamp')
+        if verbose:
+            print('config: {}'.format(ts_conf))
+            print('image:  {}'.format(ts_image))
+        if ts_image and ts_image > ts_conf:
+            if verbose:
+                print('image: {} up-to-date'.format(image_name))
+            image = client.images.get(tag)
+            return image
+
     image = conf.get('image')
     packages = conf['packages']
     dockerfile = conf['dockerfile']
@@ -91,7 +113,6 @@ def build_image(client, conf, update, verbose):
         dockerfile.insert(0, 'FROM {}'.format(image))
     for p in packages:
         dockerfile.append(pkginstall.format(p))
-    tag = make_image_name(conf['osname'])
     try:
         if verbose:
             # fallback to external command 'docker build' as there is
@@ -112,6 +133,14 @@ def build_image(client, conf, update, verbose):
                 print('Built image {} / {}'.format(image.tags[0], image.short_id))
                 for l in logs:
                     print(l.get('stream', '').strip('\n'))
+
+        if not os.path.exists(cache_dir):
+            os.mkdir(cache_dir)
+        with open(cache_file, 'w') as file:
+            if verbose:
+                print('cache: {}'.format(cache_file))
+            file.write('')
+
     except (docker.errors.BuildError, KeyboardInterrupt, subprocess.CalledProcessError, docker.errors.ImageNotFound) as e:
         print('Build Error: {}'.format(e))
         print()

setup.py

@@ -14,6 +14,7 @@ setup(
         "pathlib",
         "pyxdg",
         "pyyaml",
+        "pytz",
     ],
     entry_points={
         "console_scripts": [