Implement RAOBSounding class

Implement RAOBSounding class to allow incremental parsing of a sounding
from separate observation blocks

lib/xmet/map.py

@@ -44,7 +44,7 @@ class EquirectMap():
         rect.width  = width
         rect.height = height
 
-        svg.render_layer(cr, None, rect)
+        svg.render_document(cr, rect)
 
     def draw_base_map_from_file(self,
                                 cr: cairo.Context,

lib/xmet/raob.py

@@ -15,6 +15,85 @@ def meters_second(knots: float) -> float:
 class RAOBReaderException(Exception):
     ...
 
+class RAOBSounding():
+    DATA_SOURCE = 'UCAR'
+
+    station:   str
+    timestamp: str
+    samples:   dict[float, SoundingSample]
+
+    def __init__(self, station: str, timestamp: str):
+        self.station   = station
+        self.timestamp = timestamp
+        self.samples   = dict()
+
+    def parse_timestamp(self, token: str):
+        if token[0:2] == '//':
+            return None
+
+        day  = int(token[0:2])
+        hour = int(token[2:4])
+
+        now = datetime.datetime.now(datetime.UTC)
+
+        return datetime.datetime(
+            year  = now.year,
+            month = now.month,
+            day   = day if day < 51 else day - 50,
+            hour  = hour
+        )
+
+    def finish(self) -> Sounding:
+        timestamp = self.parse_timestamp(self.timestamp)
+
+        sounding = Sounding()
+        sounding.samples = list()
+        sounding.station = self.station
+
+        sounding.data_source_pressure = self.DATA_SOURCE
+        sounding.data_source_other    = self.DATA_SOURCE
+        sounding.timestamp_observed   = timestamp
+        sounding.timestamp_released   = timestamp - datetime.timedelta(minutes=45)
+
+        for pressure in sorted(self.samples.keys(), reverse=True):
+            sounding.samples.append(self.samples[pressure])
+
+        return sounding
+
+    def sample(self, pressure: float):
+        if pressure in self.samples:
+            return self.samples[pressure]
+
+        sample = SoundingSample()
+        sample.pressure    = pressure
+        sample.pressure_qa = ' '
+        sample.height_qa   = ' '
+        sample.temp_qa     = ' '
+
+        self.samples[pressure] = sample
+
+        return sample
+
+    def record_height(self, pressure: float, height: float):
+        sample = self.sample(pressure)
+        sample.height = height
+
+    def record_temp_dewpoint(self,
+                             pressure: float,
+                             temp: float,
+                             dewpoint: float):
+        sample = self.sample(pressure)
+        sample.temp     = temp
+        sample.dewpoint = dewpoint
+
+    def record_wind_speed_dir(self,
+                              pressure: float,
+                              wind_speed: float,
+                              wind_dir: float):
+        sample = self.sample(pressure)
+        sample.wind_speed = wind_speed
+        sample.wind_dir   = wind_dir
+
 class RAOBObs():
     DATA_SOURCE = 'UCAR'