Implement search provider (#201)

* Begin work on search provider

* Initial search provider work, organize meson

* Initial work on icons

* Implement LaunchSearch

* Don't hold arbitrary reference to service

I don't know why Lollypop does this

* Send notification, pad images

* Update translations

* Fix init_search_term typing

cartridges/importer/source.py

@@ -0,0 +1,126 @@
+# source.py
+#
+# Copyright 2023 Geoffrey Coulaud
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+import sys
+from abc import abstractmethod
+from collections.abc import Iterable
+from typing import Any, Collection, Generator, Optional
+
+from cartridges.game import Game
+from cartridges.importer.location import Location
+
+# Type of the data returned by iterating on a Source
+SourceIterationResult = Optional[Game | tuple[Game, tuple[Any]]]
+
+
+class SourceIterable(Iterable):
+    """Data producer for a source of games"""
+
+    source: "Source"
+
+    def __init__(self, source: "Source") -> None:
+        self.source = source
+
+    @abstractmethod
+    def __iter__(self) -> Generator[SourceIterationResult, None, None]:
+        """
+        Method that returns a generator that produces games
+        * Should be implemented as a generator method
+        * May yield `None` when an iteration hasn't produced a game
+        * In charge of handling per-game errors
+        * Returns when exhausted
+        """
+
+
+class Source(Iterable):
+    """Source of games. E.g an installed app with a config file that lists game directories"""
+
+    source_id: str
+    name: str
+    variant: Optional[str] = None
+    available_on: set[str] = set()
+    iterable_class: type[SourceIterable]
+
+    # NOTE: Locations must be set at __init__ time, not in the class definition.
+    # They must not be shared between source instances.
+    locations: Collection[Location]
+
+    @property
+    def full_name(self) -> str:
+        """The source's full name"""
+        full_name_ = self.name
+        if self.variant:
+            full_name_ += f" ({self.variant})"
+        return full_name_
+
+    @property
+    def game_id_format(self) -> str:
+        """The string format used to construct game IDs"""
+        return self.source_id + "_{game_id}"
+
+    @property
+    def is_available(self) -> bool:
+        return sys.platform in self.available_on
+
+    def make_executable(self, *args, **kwargs) -> str:
+        """
+        Create a game executable command.
+        Should be implemented by child classes.
+        """
+
+    def __iter__(self) -> Generator[SourceIterationResult, None, None]:
+        """
+        Get an iterator for the source
+        :raises UnresolvableLocationError: Not iterable if any of the locations are unresolvable
+        """
+        for location in self.locations:
+            location.resolve()
+        return iter(self.iterable_class(self))
+
+
+class ExecutableFormatSource(Source):
+    """Source class that uses a simple executable format to start games"""
+
+    @property
+    @abstractmethod
+    def executable_format(self) -> str:
+        """The executable format used to construct game executables"""
+
+    def make_executable(self, *args, **kwargs) -> str:
+        """Use the executable format to"""
+        return self.executable_format.format(*args, **kwargs)
+
+
+# pylint: disable=abstract-method
+class URLExecutableSource(ExecutableFormatSource):
+    """Source class that use custom URLs to start games"""
+
+    url_format: str
+
+    @property
+    def executable_format(self) -> str:
+        match sys.platform:
+            case "win32":
+                return "start " + self.url_format
+            case "linux":
+                return "xdg-open " + self.url_format
+            case other:
+                raise NotImplementedError(
+                    f"No URL handler command available for {other}"
+                )