Add support for pretty-printing of dates

The KMP protocol implements a few different date/time formats. Instead
of showing raw numbers, let's show a nice, properly formatted date.

I do not feel like changing the RegisterOutput to support many native
Python types, IMHO it's perfectly OK to stick with numbers (which will
be typically fed to a time series DB or something similar) and
"everything else", but let's print that "everything else" properly.

I'm not 100% sure how to handle the `yy-mm-dd` format. I *think* that
it's rather uncommon to see meters with 26+ years old data record today,
which is why I decided to hardcode the year-2000 prefix. A non-public
document mentions '99:12:31' as an example, though.

Also, a proper y/m/d separator is definitely `-`, not `:`, so I'm using
that for clarity.

Author: jktjkt

src/pykmp/registers.py

@@ -25,9 +25,9 @@ class RegisterOutput:
     unit_int: int
     unit_hex: str = attrs.field(init=False)
     unit_str: str = attrs.field(init=False)
-    value_float: float = attrs.field(init=False)
-    value_str: str = attrs.field(init=False)  # best: uses decimal.Decimal without loss
-    value_dec: decimal.Decimal
+    value_float: float = attrs.field(init=False, default=None)
+    value_str: str = attrs.field()  # best: uses decimal.Decimal without loss
+    value_dec: decimal.Decimal = attrs.field()
 
     def __attrs_post_init__(self) -> None:
         self.id_hex = f"0x{self.id_int:04X}"
@@ -36,16 +36,36 @@ def __attrs_post_init__(self) -> None:
         self.unit_str = constants.UNITS_NAMES.get(
             self.unit_int, f"<unknown unit {self.unit_int}>"
         )
-        self.value_float = float(self.value_dec)
-        self.value_str = str(self.value_dec)
+        if self.value_dec is not None:
+            self.value_float = float(self.value_dec)
+            self.value_str = str(self.value_dec)
 
     @classmethod
     def from_register_data(cls, reg: messages.RegisterData) -> Self:
-        value_dec = codec.FloatCodec.decode(reg.value)
+        value_dec = None
+        value_str = None
+        match reg.unit:
+            case 0x2f:
+                # hh:mm:ss
+                d = int.from_bytes(reg.value[2:], 'big')
+                value_str = f'{(d//10000):02}:{(d // 100 % 100):02}:{(d % 100):02}'
+                pass
+            case 0x30:
+                # yy-mm-dd
+                d = int.from_bytes(reg.value[2:], 'big')
+                value_str = f'{(2000 + d//10000):02}-{(d // 100 % 100):02}-{(d % 100):02}'
+                pass
+            case 0x32:
+                # mm-dd
+                d = int.from_bytes(reg.value[2:], 'big')
+                value_str = f'{(d // 100 % 100):02}-{(d % 100):02}'
+            case _:
+                value_dec = codec.FloatCodec.decode(reg.value)
         return cls(
             id_int=reg.id_,
             unit_int=reg.unit,
             value_dec=value_dec,
+            value_str=value_str,
         )
 
     def to_pretty_line(self) -> str:

tests/test_registers.py

@@ -28,6 +28,30 @@
             decimal.Decimal('378.022'),
             'GJ',
         ),
+        pytest.param(
+            1002,
+            47,
+            '04 00 00 00 00 04',
+            '00:00:04',
+            None,
+            'hh:mm:ss',
+        ),
+        pytest.param(
+            1003,
+            48,
+            '04 00 00 03 ae 4f',
+            '2024-12-31',
+            None,
+            'yy:mm:dd',
+        ),
+        pytest.param(
+            0,
+            50,
+            '04 00 00 03 38',
+            '08-24',
+            None,
+            'mm:dd',
+        ),
     ]
 )
 def test_register_parsing(id_, unit, blob_with_size, value_str, value_dec, unit_str):