SoftSignalBackend wrapping arbitrary callables

src/ophyd_async/core/_soft_signal_backend.py

@@ -1,9 +1,10 @@
 from __future__ import annotations
 
+import asyncio
 import time
 import typing
 from abc import abstractmethod
-from collections.abc import Sequence
+from collections.abc import Awaitable, Callable, Sequence
 from dataclasses import dataclass
 from functools import lru_cache
 from typing import Any, Generic, get_args
@@ -29,9 +30,6 @@
 
 
 class SoftConverter(Generic[SignalDatatypeT]):
-    # This is Any -> SignalDatatypeT because we support coercing
-    # value types to SignalDatatype to allow people to do things like
-    # SignalRW[Enum].set("enum value")
     @abstractmethod
     def write_value(self, value: Any) -> SignalDatatypeT: ...
 
@@ -114,6 +112,10 @@ def make_converter(datatype: type[SignalDatatype]) -> SoftConverter:
     raise TypeError(f"Can't make converter for {datatype}")
 
 
+Setter = Callable[[Any], SignalDatatypeT | None | Awaitable[SignalDatatypeT | None]]
+Getter = Callable[[], SignalDatatypeT | Awaitable[SignalDatatypeT]]
+
+
 class SoftSignalBackend(SignalBackend[SignalDatatypeT]):
     """An backend to a soft Signal, for test signals see [](#MockSignalBackend).
 
@@ -124,6 +126,16 @@ class SoftSignalBackend(SignalBackend[SignalDatatypeT]):
     :param units: The units for numeric datatypes.
     :param precision:
         The number of digits after the decimal place to display for a float datatype.
+    :param getter:
+        Optional callable returning the current device value, called on
+        get_value/get_reading and periodically if poll_period is set.
+    :param setter:
+        Optional callable performing the set action. May return the settled
+        value; if it returns None and a getter is configured, the getter is
+        called to refresh the cache.
+    :param poll_period:
+        How often (seconds) to call the getter while a subscription is active.
+        Requires getter to be set.
     """
 
     def __init__(
@@ -132,18 +144,51 @@ def __init__(
         initial_value: SignalDatatypeT | None = None,
         units: str | None = None,
         precision: int | None = None,
+        *,
+        getter: Getter[SignalDatatypeT] | None = None,
+        setter: Setter[SignalDatatypeT] | None = None,
+        poll_period: float | None = None,
     ):
-        # Create the right converter for the datatype
+        if poll_period is not None and getter is None:
+            raise ValueError("poll_period requires a getter to be set")
         self.converter = make_converter(datatype or float)
-        # Add the extra static metadata to the dictionary
         self.metadata = make_metadata(datatype, units, precision)
-        # Create and set the initial value
         self.initial_value = self.converter.write_value(initial_value)
         self.reading: Reading[SignalDatatypeT]
         self.callback: Callback[Reading[SignalDatatypeT]] | None = None
+        self._getter = getter
+        self._setter = setter
+        self._poll_period = poll_period
+        self._poll_task: asyncio.Task | None = None
         self.set_value(self.initial_value)
         super().__init__(datatype)
 
+    async def _call_getter(self) -> SignalDatatypeT:
+        if self._getter is None:
+            raise RuntimeError("No getter configured")
+        result = self._getter()
+        if isinstance(result, Awaitable):
+            result = await result
+        return self.converter.write_value(result)
+
+    async def _call_setter(self, value: Any) -> SignalDatatypeT | None:
+        if self._setter is None:
+            raise RuntimeError("No setter configured")
+        result = self._setter(value)
+        if isinstance(result, Awaitable):
+            result = await result
+        return result
+
+    async def _poll(self) -> None:
+        if self._poll_period is None:
+            raise RuntimeError("No poll_period configured")
+        while True:
+            await asyncio.sleep(self._poll_period)
+            try:
+                self.set_value(await self._call_getter())
+            except Exception:
+                continue
+
     def set_value(self, value: SignalDatatypeT):
         """Set the current value, alarm and timestamp."""
         self.reading = Reading(
@@ -160,19 +205,32 @@ def source(self, name: str, read: bool) -> str:
     async def connect(self, timeout: float):
         pass
 
-    async def put(self, value: SignalDatatypeT | None) -> None:
+    async def put(self, value: Any) -> None:
         write_value = self.initial_value if value is None else value
-        self.set_value(write_value)
+        if self._setter is not None:
+            settled = await self._call_setter(write_value)
+            if settled is not None:
+                self.set_value(self.converter.write_value(settled))
+            elif self._getter is not None:
+                self.set_value(await self._call_getter())
+            else:
+                self.set_value(self.converter.write_value(write_value))
+        else:
+            self.set_value(write_value)
 
     async def get_datakey(self, source: str) -> DataKey:
         return make_datakey(
             self.datatype or float, self.reading["value"], source, self.metadata
         )
 
     async def get_reading(self) -> Reading[SignalDatatypeT]:
+        if self._getter is not None:
+            self.set_value(await self._call_getter())
         return self.reading
 
     async def get_value(self) -> SignalDatatypeT:
+        if self._getter is not None:
+            self.set_value(await self._call_getter())
         return self.reading["value"]
 
     async def get_setpoint(self) -> SignalDatatypeT:
@@ -184,4 +242,10 @@ def set_callback(self, callback: Callback[Reading[SignalDatatypeT]] | None) -> N
             raise RuntimeError("Cannot set a callback when one is already set")
         if callback:
             callback(self.reading)
+            if self._poll_period is not None:
+                self._poll_task = asyncio.get_event_loop().create_task(self._poll())
+        else:
+            if self._poll_task is not None:
+                self._poll_task.cancel()
+                self._poll_task = None
         self.callback = callback

tests/unit_tests/core/test_soft_signal_backend.py

@@ -204,3 +204,234 @@ async def test_soft_signal_coerces_numpy_types():
     soft_signal._connector.backend.set_value(np.float64(2.2))
     assert await soft_signal.get_value() == 2.2
     assert type(await soft_signal.get_value()) is float
+
+
+async def test_soft_signal_backend_getter():
+    store = [42.0]
+    backend = SoftSignalBackend(float, getter=lambda: store[0])
+    await backend.connect(timeout=1)
+    assert await backend.get_value() == 42.0
+    store[0] = 99.0
+    assert await backend.get_value() == 99.0
+
+
+async def test_soft_signal_backend_async_getter():
+    store = [42.0]
+
+    async def getter():
+        return store[0]
+
+    backend = SoftSignalBackend(float, getter=getter)
+    await backend.connect(timeout=1)
+    store[0] = 99.0
+    assert await backend.get_value() == 99.0
+
+
+async def test_soft_signal_backend_getter_updates_reading():
+    store = [1.0]
+    backend = SoftSignalBackend(float, getter=lambda: store[0])
+    await backend.connect(timeout=1)
+    store[0] = 2.0
+    reading = await backend.get_reading()
+    assert reading["value"] == 2.0
+
+
+async def test_soft_signal_backend_getter_does_not_affect_setpoint():
+    store = [1.0]
+    backend = SoftSignalBackend(float, getter=lambda: store[0])
+    await backend.connect(timeout=1)
+    await backend.put(5.0)
+    store[0] = 99.0
+    assert await backend.get_setpoint() == 5.0
+    assert await backend.get_value() == 99.0
+
+
+async def test_soft_signal_backend_setter_homogeneous_types():
+    store = [0.0]
+    backend = SoftSignalBackend(float, setter=lambda v: store.__setitem__(0, v))
+    await backend.connect(timeout=1)
+    await backend.put(7.0)
+    assert store[0] == 7.0
+
+
+async def test_soft_signal_backend_setter_heterogeneous_types():
+    counts_written = []
+
+    def counts_setter(counts: int) -> float:
+        counts_written.append(counts)
+        return counts * 0.01
+
+    backend = SoftSignalBackend(float, setter=counts_setter)
+    await backend.connect(timeout=1)
+    await backend.put(1000)
+    assert counts_written == [1000]
+    assert await backend.get_value() == pytest.approx(10.0)
+
+
+async def test_soft_signal_backend_async_setter_heterogeneous_types():
+    counts_written = []
+
+    async def counts_setter(counts: int) -> float:
+        counts_written.append(counts)
+        return counts * 0.01
+
+    backend = SoftSignalBackend(float, setter=counts_setter)
+    await backend.connect(timeout=1)
+    await backend.put(500)
+    assert counts_written == [500]
+    assert await backend.get_value() == pytest.approx(5.0)
+
+
+async def test_soft_signal_backend_setter_heterogeneous_none_return_with_getter():
+    store = [0.0]
+    commands = []
+
+    def command_setter(cmd: str) -> None:
+        commands.append(cmd)
+        store[0] = float(cmd.split("=")[1])
+
+    backend = SoftSignalBackend(float, setter=command_setter, getter=lambda: store[0])
+    await backend.connect(timeout=1)
+    await backend.put("pos=42.5")
+    assert commands == ["pos=42.5"]
+    assert await backend.get_value() == pytest.approx(42.5)
+
+
+async def test_soft_signal_backend_setter_heterogeneous_none_return_without_getter():
+    received = []
+
+    def int_setter(v: int) -> None:
+        received.append(v)
+
+    backend = SoftSignalBackend(float, setter=int_setter)
+    await backend.connect(timeout=1)
+    await backend.put(42)
+    assert received == [42]
+    assert await backend.get_value() == pytest.approx(42.0)
+
+
+async def test_soft_signal_backend_async_setter():
+    store = [0.0]
+
+    async def setter(v):
+        store[0] = v
+
+    backend = SoftSignalBackend(float, setter=setter)
+    await backend.connect(timeout=1)
+    await backend.put(7.0)
+    assert store[0] == 7.0
+
+
+async def test_soft_signal_backend_setter_returns_settled_value():
+    def clamping_setter(v):
+        return max(0.0, min(10.0, v))
+
+    backend = SoftSignalBackend(float, setter=clamping_setter)
+    await backend.connect(timeout=1)
+    await backend.put(50.0)
+    assert await backend.get_value() == 10.0
+
+
+async def test_soft_signal_backend_setter_none_with_getter_refreshes():
+    store = [0.0]
+
+    def setter(v):
+        store[0] = v
+
+    backend = SoftSignalBackend(float, setter=setter, getter=lambda: store[0])
+    await backend.connect(timeout=1)
+    await backend.put(3.0)
+    assert await backend.get_value() == 3.0
+
+
+async def test_soft_signal_backend_setter_none_without_getter_stores_write_value():
+    called_with = []
+
+    def setter(v):
+        called_with.append(v)
+
+    backend = SoftSignalBackend(float, setter=setter)
+    await backend.connect(timeout=1)
+    await backend.put(6.0)
+    assert called_with == [6.0]
+    assert await backend.get_value() == 6.0
+
+
+async def test_soft_signal_backend_poll_period_without_getter_raises():
+    with pytest.raises(ValueError, match="poll_period requires a getter"):
+        SoftSignalBackend(float, poll_period=0.1)
+
+
+async def test_soft_signal_backend_poll_period_updates_via_callback():
+    store = [0.0]
+    backend = SoftSignalBackend(float, getter=lambda: store[0], poll_period=0.05)
+    await backend.connect(timeout=1)
+
+    updates: asyncio.Queue[Reading] = asyncio.Queue()
+    backend.set_callback(updates.put_nowait)
+
+    # Consume the initial callback fired by set_callback
+    await updates.get()
+
+    store[0] = 5.0
+    reading = await asyncio.wait_for(updates.get(), timeout=1.0)
+    assert reading["value"] == 5.0
+
+    backend.set_callback(None)
+
+
+async def test_soft_signal_backend_poll_task_starts_and_stops():
+    backend = SoftSignalBackend(float, getter=lambda: 0.0, poll_period=0.05)
+    await backend.connect(timeout=1)
+
+    updates: asyncio.Queue[Reading] = asyncio.Queue()
+    assert backend._poll_task is None
+
+    backend.set_callback(updates.put_nowait)
+    assert backend._poll_task is not None
+    assert not backend._poll_task.cancelled()
+
+    backend.set_callback(None)
+    assert backend._poll_task is None
+
+
+async def test_soft_signal_backend_no_poll_without_poll_period():
+    # A getter without poll_period should not start a background task.
+    backend = SoftSignalBackend(float, getter=lambda: 0.0)
+    await backend.connect(timeout=1)
+
+    updates: asyncio.Queue[Reading] = asyncio.Queue()
+    backend.set_callback(updates.put_nowait)
+    assert backend._poll_task is None
+    backend.set_callback(None)
+
+
+async def test_soft_signal_backend_setter_accepts_config_object():
+
+    class MotorConfig:
+        velocity: float
+        acceleration: float
+        units: str
+
+    configs_received = []
+    store = [0.0]
+
+    def config_setter(config: MotorConfig) -> float:
+        configs_received.append(config)
+        store[0] = config.velocity
+        return config.velocity
+
+    backend = SoftSignalBackend(float, setter=config_setter)
+    await backend.connect(timeout=1)
+
+    cfg = MotorConfig()
+    cfg.velocity = 2.5
+    cfg.acceleration = 0.1
+    cfg.units = "mm/s"
+    await backend.put(cfg)
+
+    assert len(configs_received) == 1
+    assert configs_received[0].velocity == 2.5
+    assert configs_received[0].acceleration == 0.1
+    assert configs_received[0].units == "mm/s"
+    assert await backend.get_value() == pytest.approx(2.5)