prepare initialisation of blockchain

src/dopt_pollublock_blockchain/blockchain.pyx

@@ -431,7 +431,10 @@ cdef class Blockchain:
 
     # // Python public API
     def __len__(self):
-        return self._index + 1
+        if self.genesis_done:
+            return self._index + 1
+        else:
+            return 0
     
     @property
     def difficulty(self):

src/dopt_pollublock_blockchain/constants.py

@@ -0,0 +1,5 @@
+from __future__ import annotations
+
+from typing import Final
+
+BLOCKCHAIN_DIFFICULTY: Final[int] = 24

src/dopt_pollublock_blockchain/db.py

@@ -1,8 +1,10 @@
 from __future__ import annotations
 
+import polars as pl
 import sqlalchemy as sql
 
 metadata_blockchain: sql.MetaData = sql.MetaData()
+metadata_sensor_data: sql.MetaData = sql.MetaData()
 
 blocks = sql.Table(
     "blocks",
@@ -14,3 +16,23 @@ blocks = sql.Table(
     sql.Column("hash", sql.String(64), nullable=False),
     sql.Column("data", sql.String(64), nullable=False),
 )
+
+sensor_data = sql.Table(
+    "sensor_data",
+    metadata_sensor_data,
+    sql.Column("Index", sql.Integer, primary_key=True, autoincrement=True),
+    sql.Column("Datetime", sql.DateTime, nullable=False),
+    sql.Column("Temperature_(Celsius)", sql.Float, nullable=False),
+    sql.Column("Pressure_(Pa)", sql.Integer, nullable=False),
+    sql.Column("Air_Quantity_(Percent)", sql.Float, nullable=False),
+    sql.Column("Blockchain_Block_Number", sql.BigInteger, nullable=True),
+)
+
+sensor_data_query_schema: dict[str, type[pl.DataType]] = {
+    "Index": pl.UInt64,
+    "Datetime": pl.Datetime,
+    "Temperature_(Celsius)": pl.Float32,
+    "Pressure_(Pa)": pl.Int32,
+    "Air_Quantity_(Percent)": pl.Float64,
+    "Blockchain_Block_Number": pl.UInt64,
+}