Implement initial structure and core functionality for Duck Preview application

duck_preview/camera/service.py

@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+from PySide6.QtCore import QObject, Signal
+from PySide6.QtMultimedia import (
+    QCamera,
+    QCameraDevice,
+    QCameraFormat,
+    QMediaCaptureSession,
+    QMediaDevices,
+    QVideoSink,
+)
+
+
+class CameraService(QObject):
+    error_occurred = Signal(str)
+
+    def __init__(self, parent: QObject | None = None) -> None:
+        super().__init__(parent)
+        self._session = QMediaCaptureSession()
+        self._sink = QVideoSink()
+        self._session.setVideoOutput(self._sink)
+        self._camera: QCamera | None = None
+
+    @property
+    def sink(self) -> QVideoSink:
+        return self._sink
+
+    @property
+    def session(self) -> QMediaCaptureSession:
+        return self._session
+
+    @staticmethod
+    def available_cameras() -> list[QCameraDevice]:
+        return QMediaDevices.videoInputs()
+
+    def is_active(self) -> bool:
+        return self._camera is not None and self._camera.isActive()
+
+    def start(self, device: QCameraDevice) -> None:
+        self.stop()
+        self._camera = QCamera(device, self)
+        self._camera.errorOccurred.connect(self._on_error)
+        self._session.setCamera(self._camera)
+        self._camera.start()
+
+    def stop(self) -> None:
+        if self._camera is not None:
+            self._camera.stop()
+            self._session.setCamera(None)
+            self._camera.deleteLater()
+            self._camera = None
+
+    def set_camera_format(self, fmt: QCameraFormat) -> None:
+        if self._camera is not None:
+            self._camera.setCameraFormat(fmt)
+
+    def _on_error(self, error: QCamera.Error, error_string: str) -> None:
+        self.error_occurred.emit(error_string)