lib.Distro, ExecContext: Add classes, refactor lib.distro

The code below lib.distro, as left behind by the previous commit, is
geared towards being directly used as a command-line API. This commit
introduces the abstract base class Distro, a proxy for
distribution-specific interactions. The proxy abstracts distro
specifics into an API with proper method prototypes, not
argparse.Namespace contents, and can thus be more easily driven by
arbitrary code.

The Distro class is initialized with a member variable of type
ExecContext, another new class introduced by this commit. It is
designed to abstract the communication channel to the distribution
instance.  Currently only one specialization exists, Local, which
interacts with the distribution and root file system it is running
in, but is planned to be subclassed to support interaction via SSH,
serial, chroot, or chains thereof.

Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/cmds/DistroBase.py

@@ -3,6 +3,7 @@
 import re, sys
 from argparse import ArgumentParser
 
+from ..lib.Distro import Distro
 from ..App import App
 from .Cmd import Cmd as Base
 
@@ -12,7 +13,16 @@ class DistroBase(Base): # export
         self.__id = None
         super().__init__(parent, name, help)
         self._add_subcommands()
-        self.__interactive: bool|None = None
+        self.__distro: Distro|None = None
+
+    @property
+    def distro(self) -> Distro:
+        if self.__distro is None:
+            ret = Distro.instantiate(self.distro_id, ec=self.app.exec_context)
+            self.__distro = ret
+        return self.__distro
+
+    # --------------- legacy methods
 
     @property
     def distro_id(self):
@@ -28,19 +38,6 @@ class DistroBase(Base): # export
     def add_arguments(self, p: ArgumentParser) -> None:
         super().add_arguments(p)
         p.add_argument('--id', default=None, help='Distribution ID (default is taken from /etc/os-release)')
-        p.add_argument('--interactive', choices=['true', 'false', 'auto'], default='true', help="Wait for user input or try to proceed unattended")
-
-    @property
-    def interactive(self) -> bool:
-        if self.__interactive is None:
-            match self.app.args.interactive:
-                case 'true':
-                    self.__interactive = True
-                case 'false':
-                    self.__interactive = False
-                case 'auto':
-                    self.__interactive = sys.stdin.isatty()
-        return self.__interactive
 
     async def _run(self, args):
         # Missing subcommand