abstract chain features; use local imports to avoid hard dependencies

csdr/chain/demodulator.py

@@ -1,5 +1,6 @@
 from csdr.chain import Chain
 from abc import ABC, abstractmethod
+from pycsdr.modules import Writer
 
 
 class BaseDemodulatorChain(Chain):
@@ -36,3 +37,15 @@ class DialFrequencyReceiver(ABC):
 # marker interface
 class HdAudio:
     pass
+
+
+class MetaProvider(ABC):
+    @abstractmethod
+    def setMetaWriter(self, writer: Writer) -> None:
+        pass
+
+
+class SlotFilterChain(ABC):
+    @abstractmethod
+    def setSlotFilter(self, filter: int) -> None:
+        pass

csdr/chain/digiham.py

@@ -1,4 +1,4 @@
-from csdr.chain.demodulator import BaseDemodulatorChain, FixedAudioRateChain, FixedIfSampleRateChain, DialFrequencyReceiver
+from csdr.chain.demodulator import BaseDemodulatorChain, FixedAudioRateChain, FixedIfSampleRateChain, DialFrequencyReceiver, MetaProvider, SlotFilterChain
 from pycsdr.modules import FmDemod, Agc, Writer, Buffer
 from pycsdr.types import Format
 from digiham.modules import DstarDecoder, DcBlock, FskDemodulator, GfskDemodulator, DigitalVoiceFilter, MbeSynthesizer, NarrowRrcFilter, NxdnDecoder, DmrDecoder, WideRrcFilter, YsfDecoder
@@ -6,7 +6,7 @@ from digiham.ambe import Modes
 from owrx.meta import MetaParser
 
 
-class DigihamChain(BaseDemodulatorChain, FixedIfSampleRateChain, FixedAudioRateChain, DialFrequencyReceiver):
+class DigihamChain(BaseDemodulatorChain, FixedIfSampleRateChain, FixedAudioRateChain, DialFrequencyReceiver, MetaProvider):
     def __init__(self, fskDemodulator, decoder, mbeMode, filter=None, codecserver: str = ""):
         self.decoder = decoder
         if codecserver is None:
@@ -34,7 +34,7 @@ class DigihamChain(BaseDemodulatorChain, FixedIfSampleRateChain, FixedAudioRateC
     def getFixedAudioRate(self):
         return 8000
 
-    def setMetaWriter(self, writer: Writer):
+    def setMetaWriter(self, writer: Writer) -> None:
         if self.metaParser is None:
             self.metaParser = MetaParser()
             buffer = Buffer(Format.CHAR)
@@ -80,7 +80,7 @@ class Nxdn(DigihamChain):
         )
 
 
-class Dmr(DigihamChain):
+class Dmr(DigihamChain, SlotFilterChain):
     def __init__(self, codecserver: str = ""):
         super().__init__(
             fskDemodulator=GfskDemodulator(samplesPerSymbol=10),