db rate writing implemented

xexe/rate_writing.py

@@ -53,8 +53,8 @@ class DWHRateWriter(RateWriter):
         self.connection = self._create_connection()
         self._verify_prerequisites()
 
-    @abstractmethod
-    def _create_connection(self):
+    @staticmethod
+    def _create_connection():
         host = os.environ["DWH_HOST"]
         port = os.environ["DWH_PORT"]
         database = os.environ["DWH_DB"]
@@ -134,6 +134,68 @@ class DWHRateWriter(RateWriter):
             cursor.close()
             self.connection.autocommit = True  # Reset autocommit to its default state
 
+    def _create_rates_table_if_not_exists(self):
+        cursor = self.connection.cursor()
+
+        create_table_query = sql.SQL(
+            """
+            CREATE TABLE IF NOT EXISTS {}.{} (
+                from_currency CHAR(3) NOT NULL,
+                to_currency CHAR(3) NOT NULL,
+                rate DECIMAL(19, 4) NOT NULL,
+                rate_date_utc DATE NOT NULL,
+                exported_at_utc TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+                PRIMARY KEY (from_currency, to_currency, rate_date_utc)
+            );
+        """
+        ).format(sql.Identifier(DWH_SCHEMA), sql.Identifier(DWH_TABLE))
+
+        try:
+            cursor.execute(create_table_query)
+            self.connection.commit()
+        except Exception as e:
+            self.connection.rollback()
+            raise Exception(
+                f"Failed to create table '{DWH_TABLE}' in schema '{DWH_SCHEMA}': {e}"
+            )
+        finally:
+            cursor.close()
+
+    def write_rates(self, rates: ExchangeRates) -> None:
+        self._create_rates_table_if_not_exists()
+
+        cursor = self.connection.cursor()
+        insert_query = sql.SQL(
+            """
+            INSERT INTO {}.{} (from_currency, to_currency, rate, rate_date_utc, exported_at_utc)
+            VALUES (%s, %s, %s, %s, CURRENT_TIMESTAMP)
+            ON CONFLICT (from_currency, to_currency, rate_date_utc)
+            DO UPDATE SET rate = EXCLUDED.rate, exported_at_utc = EXCLUDED.exported_at_utc;
+        """
+        ).format(sql.Identifier(DWH_SCHEMA), sql.Identifier(DWH_TABLE))
+
+        self.connection.autocommit = False
+        try:
+            for rate in rates:
+                cursor.execute(
+                    insert_query,
+                    (
+                        rate.from_currency.value,
+                        rate.to_currency.value,
+                        rate.amount,
+                        rate.rate_date,
+                    ),
+                )
+            self.connection.commit()
+        except Exception as e:
+            self.connection.rollback()
+            raise Exception(
+                f"Failed to write rates to table '{DWH_TABLE}' in schema '{DWH_SCHEMA}': {e}"
+            )
+        finally:
+            cursor.close()
+            self.connection.autocommit = True
+
 
 def build_rate_writer(output: str) -> RateWriter:
     output_is_csv_file_path = bool(pathlib.Path(output).suffix == ".csv")