package: Introduce component API for package conflicts

This is help in eliminating the module level package_conflicts declarations.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/package.py

@@ -3,12 +3,13 @@
 Framework for installing and updating distribution packages
 """
 
+import enum
 import json
 import logging
 import subprocess
 import sys
 import threading
-from typing import Union
+from typing import Optional, Union
 
 import apt.cache
 from django.utils.translation import gettext as _
@@ -28,8 +29,15 @@ class Packages(app.FollowerComponent):
     of packages required by an app.
     """
 
+    class ConflictsAction(enum.Enum):
+        """Action to take when a conflicting package is installed."""
+        IGNORE = 'ignore'  # Proceed as if there are no conflicts
+        REMOVE = 'remove'  # Remove the packages before installing the app
+
     def __init__(self, component_id: str, packages: list[str],
-                 skip_recommends=False):
+                 skip_recommends: bool = False,
+                 conflicts: Optional[list[str]] = None,
+                 conflicts_action: Optional[ConflictsAction] = None):
         """Initialize a new packages component.
 
         'component_id' should be a unique ID across all components of an app
@@ -39,12 +47,22 @@ class Packages(app.FollowerComponent):
 
         'skip_recommends' is a boolean specifying whether recommended packages
         should be installed along with the listed packages.
+
+        'conflicts' is the list of Debian packages that can't simultaneously be
+        installed with packages listed here. None if there are no known
+        conflicting packages.
+
+        'conflicts_action' is a string representing the action to take when it
+        is found that conflicting Debian packages are installed on the system.
+        None if there are no known conflicting packages.
         """
         super().__init__(component_id)
 
         self.component_id = component_id
         self._packages = packages
         self.skip_recommends = skip_recommends
+        self.conflicts = conflicts
+        self.conflicts_action = conflicts_action
 
     @property
     def packages(self) -> list[str]:
@@ -59,6 +77,13 @@ class Packages(app.FollowerComponent):
         helper = module.setup_helper
         helper.install(self.packages, skip_recommends=self.skip_recommends)
 
+    def find_conflicts(self) -> Optional[list[str]]:
+        """Return list of conflicting packages installed on the system."""
+        if not self.conflicts:
+            return None
+
+        return packages_installed(self.conflicts)
+
 
 class PackageException(Exception):
     """A package operation has failed."""

plinth/tests/test_package.py

@@ -20,13 +20,19 @@ def test_packages_init():
     assert component.component_id == 'test-component'
     assert component.packages == ['foo', 'bar']
     assert not component.skip_recommends
+    assert component.conflicts is None
+    assert component.conflicts_action is None
 
     with pytest.raises(ValueError):
         Packages(None, [])
 
-    component = Packages('test-component', [], skip_recommends=True)
+    component = Packages('test-component', [], skip_recommends=True,
+                         conflicts=['conflict1', 'conflict2'],
+                         conflicts_action=Packages.ConflictsAction.IGNORE)
     assert component.packages == []
     assert component.skip_recommends
+    assert component.conflicts == ['conflict1', 'conflict2']
+    assert component.conflicts_action == Packages.ConflictsAction.IGNORE
 
 
 def test_packages_setup():
@@ -54,6 +60,26 @@ def test_packages_setup():
         [call(['foo2', 'bar2'], skip_recommends=True)])
 
 
+@patch('plinth.package.packages_installed')
+def test_packages_find_conflicts(packages_installed_):
+    """Test finding conflicts."""
+    packages_installed_.return_value = []
+    component = Packages('test-component', ['package3', 'package4'])
+    assert component.find_conflicts() is None
+
+    packages_installed_.return_value = []
+    component = Packages('test-component', ['package3', 'package4'],
+                         conflicts=['package5', 'package6'],
+                         conflicts_action=Packages.ConflictsAction.IGNORE)
+    assert component.find_conflicts() == []
+
+    packages_installed_.return_value = ['package1', 'package2']
+    component = Packages('test-component', ['package3', 'package4'],
+                         conflicts=['package1', 'package2'],
+                         conflicts_action=Packages.ConflictsAction.IGNORE)
+    assert component.find_conflicts() == ['package1', 'package2']
+
+
 def test_packages_installed():
     """Test packages_installed()."""
     # list as input