ENH: use very custom hdf5 filestore plugins

Do not assume each point as the same number of frames, requires
changes to the schema of the resource and datum + a new handler.

startup/10-area-detector.py

@@ -1,5 +1,6 @@
 from ophyd import Component as Cpt
-from ophyd.areadetector.filestore_mixins import FileStoreHDF5IterativeWrite
+from ophyd.areadetector.filestore_mixins import (
+    FileStoreHDF5IterativeWrite, FileStoreIterativeWrite, FileStorePluginBase)
 from ophyd import EpicsSignal, AreaDetector
 from ophyd import (
     ImagePlugin,
@@ -40,9 +41,19 @@ def ensure_nonblocking(self):
                 cpt.ensure_nonblocking()
 
 
-class HDF5PluginWithFileStore(HDF5Plugin, FileStoreHDF5IterativeWrite):
+class HDF5PluginWithFileStore(HDF5Plugin, FileStorePluginBase):
     # AD v2.2.0 (at least) does not have this. It is present in v1.9.1.
     file_number_sync = None
+    filestore_spec = 'AD_HDF5_v1'
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        # can not be class level because parent sets this in __init__ :(
+        self.stage_sigs.update([('file_template', '%s%s_%6.6d.h5'),
+                                ('file_write_mode', 'Stream'),
+                                ('capture', 1)
+                                ])
+        self._current_index = 0
 
     def get_frames_per_point(self):
         return self.parent.cam.num_images.get()
@@ -52,6 +63,21 @@ def make_filename(self):
         self._ret = super().make_filename()
         return self._ret
 
+    def stage(self):
+        super().stage()
+        self._current_index = 0
+        res_kwargs = {}
+        self._generate_resource(res_kwargs)
+
+    def generate_datum(self, key, timestamp, datum_kwargs):
+        step = self.get_frames_per_point()
+        self._current_index += step
+
+        datum_kwargs = datum_kwargs or {}
+        datum_kwargs.update({'offset': self._current_index,
+                             'num_frames': step})
+        return super().generate_datum(key, timestamp, datum_kwargs)
+
 
 class AndorKlass(SingleTriggerV33, DetectorBase):
     cam = Cpt(AndorCam, "cam1:")