Store created elements in a local SQLite database

Closes #41 (closed)

arkindex_worker/cache.py

 # -*- coding: utf-8 -*-
-import os
 import sqlite3
 
+from arkindex_worker import logger
+
+SQL_ELEMENTS_TABLE_CREATION = """CREATE TABLE IF NOT EXISTS elements (
+    id VARCHAR(32) PRIMARY KEY,
+    parent_id VARCHAR(32),
+    name TEXT NOT NULL,
+    type TEXT NOT NULL,
+    polygon TEXT,
+    worker_version_id VARCHAR(32)
+)"""
+
 
 class LocalDB(object):
     def __init__(self, path):
-        if not os.path.exists(path):
-            open(path, "x").close()
-
         self.db = sqlite3.connect(path)
+        self.db.row_factory = sqlite3.Row
         self.cursor = self.db.cursor()
+        logger.info(f"Connection to local cache {path} established.")
 
-    def create_elements_table(self):
-        try:
-            self.cursor.execute(
-                """CREATE TABLE elements (
-                id TEXT PRIMARY KEY,
-                parent_id TEXT,
-                name TEXT NOT NULL,
-                type TEXT NOT NULL,
-                polygon TEXT,
-                worker_version_id TEXT
-            )"""
-            )
-        except sqlite3.OperationalError:
-            print("Table 'elements' already exists")
+    def create_tables(self):
+        self.cursor.execute(SQL_ELEMENTS_TABLE_CREATION)
 
     def insert(self, table, lines):
-        self.cursor.executemany(f"INSERT INTO {table} VALUES (?,?,?,?,?,?)", lines)
+        if not lines:
+            return
+        columns = ", ".join(lines[0].keys())
+        placeholders = ", ".join("?" * len(lines[0]))
+        values = [tuple(line.values()) for line in lines]
+        self.cursor.executemany(
+            f"INSERT INTO {table} ({columns}) VALUES ({placeholders})", values
+        )
         self.db.commit()