Fix issues with metadata not correctly computed

src/j1939_decoder.py

@@ -17,27 +17,28 @@ def decode_j1939_metadata(lf: pl.LazyFrame) -> pl.LazyFrame:
     Decodes J1939 fields and bundles them into a Struct column.
     """
     id_int = pl.col("ID").str.to_integer(base=16).cast(pl.UInt32)
-    mask = get_j1939_mask()
 
-    priority = (id_int // 67108864) % 8
-    pf = (id_int // 65536) % 256
-    ps = (id_int // 256) % 256
-    sa = id_int % 256
+    id_shifted_8 = id_int // 256
+    id_shifted_16 = id_int // 65536
+
+    priority = ((id_int // 67108864) % 8).cast(pl.UInt8)
+    pf = (id_shifted_16 % 256).cast(pl.UInt8)
+    ps = (id_shifted_8 % 256).cast(pl.UInt8)
+    sa = (id_int % 256).cast(pl.UInt8)
 
     da = pl.when(pf < 240).then(ps).otherwise(pl.lit(255, dtype=pl.UInt8))
-    pgn = pl.when(pf < 240).then((id_int // 256) % 65536).otherwise((id_int // 256) % 262144).cast(pl.UInt32)
 
-    j1939_struct = pl.struct([
-        priority.cast(pl.UInt8).alias("Priority"),
-        pf.cast(pl.UInt8).alias("PF"),
-        ps.cast(pl.UInt8).alias("PS"),
-        sa.cast(pl.UInt8).alias("SA"),
-        da.cast(pl.UInt8).alias("DA"),
-        pgn.alias("PGN")
-    ])
+    pgn = pl.when(pf < 240).then(id_shifted_8 % 65536).otherwise(id_shifted_8 % 262144).cast(pl.UInt32)
 
     return lf.with_columns(
-        pl.when(mask).then(j1939_struct).otherwise(None).alias("j1939_metadata")
+        pl.struct([
+            priority.alias("Priority"),
+            pf.alias("PF"),
+            ps.alias("PS"),
+            sa.alias("SA"),
+            da.alias("DA"),
+            pgn.alias("PGN")
+        ]).alias("j1939_metadata")
     )
 
 if __name__ == "__main__":