Make crontab configurable

src/restic_compose_backup/cron.py

@@ -0,0 +1,69 @@
+"""
+# ┌───────────── minute (0 - 59)
+# │ ┌───────────── hour (0 - 23)
+# │ │ ┌───────────── day of the month (1 - 31)
+# │ │ │ ┌───────────── month (1 - 12)
+# │ │ │ │ ┌───────────── day of the week (0 - 6) (Sunday to Saturday;
+# │ │ │ │ │                                   7 is also Sunday on some systems)
+# │ │ │ │ │
+# │ │ │ │ │
+# * * * * * command to execute
+"""
+QUOTE_CHARS = ['"', "'"]
+
+
+def generate_crontab(config):
+    """Generate a crontab entry for running backup job"""
+    command = config.cron_command.strip()
+    schedule = config.cron_schedule
+
+    if schedule:
+        schedule = schedule.strip()
+        schedule = strip_quotes(schedule)
+        if not validate_schedule(schedule):
+            schedule = config.default_crontab_schedule
+    else:
+        schedule = config.default_crontab_schedule
+
+    return f'{schedule} {command}\n'
+
+
+def validate_schedule(schedule: str):
+    """Validate crontab format"""
+    parts = schedule.split()
+    if len(parts) != 5:
+        return False
+
+    for p in parts:
+        if p != '*' and not p.isdigit():
+            return False
+
+    minute, hour, day, month, weekday = parts
+    try:
+        validate_field(minute, 0, 59)
+        validate_field(hour, 0, 23)
+        validate_field(day, 1, 31)
+        validate_field(month, 1, 12)
+        validate_field(weekday, 0, 6)
+    except ValueError:
+        return False
+
+    return True
+
+
+def validate_field(value, min, max):
+    if value == '*':
+        return
+
+    i = int(value)
+    return min <= i <= max
+
+
+def strip_quotes(value: str):
+    """Strip enclosing single or double quotes if present"""
+    if value[0] in QUOTE_CHARS:
+        value = value[1:]
+    if value[-1] in QUOTE_CHARS:
+        value = value[:-1]
+
+    return value