Implement database connection and migration setup; add .gitignore entries

.gitignore

@@ -1,2 +1,4 @@
 build/
+instance/
 *.class
+*.db

Main.java

@@ -1,5 +1,11 @@
+import java.sql.Connection;
+import java.sql.SQLException;
+
+import src.db.Database;
+
 public class Main {
-    public static void main(String[] args) {
+    public static void main(String[] args) throws SQLException {
-        System.out.println("Hello, World!");
+        Connection conn = Database.getConnection();
+        Database.close();
     }
 }

run.sh

@@ -8,9 +8,15 @@ if ! command -v java >/dev/null 2>&1; then
     exit 1
 fi
 
-if ! javac -d build Main.java; then
+find src -name "*.java" > sources.txt
-    echo "Error: javac failed to compile Main.java."
+if ! javac -d build -cp "./extern/sqlite-jdbc-3.50.3.0.jar" @sources.txt Main.java; then
+    echo "Error: javac failed to compile sources."
     exit 1
 fi
+rm sources.txt
 
-java -cp build Main
+if [ ! -d "instance" ]; then
+    mkdir instance
+fi
+
+java -cp "build:./extern/sqlite-jdbc-3.50.3.0.jar" Main

src/db/Database.java

@@ -0,0 +1,29 @@
+package src.db;
+
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.SQLException;
+
+public class Database {
+    private static Connection conn;
+
+    public static Connection getConnection() throws SQLException {
+        if (conn == null || conn.isClosed()) {
+            String url = "jdbc:sqlite:instance/test.db";
+            conn = DriverManager.getConnection(url);
+            Migration.run(conn);
+        }
+
+        return conn;
+    }
+
+    public static void close() {
+        try {
+            if (conn != null && !conn.isClosed()) {
+                conn.close();
+            }
+        } catch (SQLException e) {
+            e.printStackTrace();
+        }
+    }
+}

src/db/Migration.java

@@ -0,0 +1,59 @@
+package src.db;
+
+import java.sql.Connection;
+import java.sql.Statement;
+
+public class Migration {
+    public static void run(Connection conn) {
+        try (Statement stmt = conn.createStatement()) {
+            stmt.execute("""
+                CREATE TABLE IF NOT EXISTS users (
+                    id INTEGER PRIMARY KEY AUTOINCREMENT,
+                    name TEXT NOT NULL,
+                    email TEXT NOT NULL UNIQUE,
+                    password_hash TEXT NOT NULL
+                )
+            """);
+
+            stmt.execute("""
+                CREATE TABLE IF NOT EXISTS accounts (
+                    id INTEGER PRIMARY KEY AUTOINCREMENT,
+                    owner_id INTEGER NOT NULL,
+                    type TEXT CHECK(type IN ('CHECKING','SAVINGS','CREDIT')) NOT NULL,
+                    account_number TEXT NOT NULL UNIQUE,
+                    bank_code TEXT NOT NULL,
+                    balance REAL NOT NULL DEFAULT 0,
+                    FOREIGN KEY(owner_id) REFERENCES users(id)
+                )
+            """);
+
+            stmt.execute("""
+                CREATE TABLE IF NOT EXISTS giro_accounts (
+                    id INTEGER PRIMARY KEY,
+                    overdraft_limit REAL DEFAULT 0,
+                    FOREIGN KEY(id) REFERENCES accounts(id) ON DELETE CASCADE
+                )
+            """);
+
+            stmt.execute("""
+                CREATE TABLE IF NOT EXISTS spar_accounts (
+                    id INTEGER PRIMARY KEY,
+                    interest_rate REAL DEFAULT 0,
+                    FOREIGN KEY(id) REFERENCES accounts(id) ON DELETE CASCADE
+                )
+            """);
+
+            stmt.execute("""
+                CREATE TABLE IF NOT EXISTS kredit_accounts (
+                    id INTEGER PRIMARY KEY,
+                    credit_limit REAL DEFAULT 0,
+                    repayment_plan TEXT,
+                    FOREIGN KEY(id) REFERENCES accounts(id) ON DELETE CASCADE
+                )
+            """);
+
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+}

src/models/Model.java

@@ -0,0 +1,16 @@
+package src.models;
+
+import java.sql.Connection;
+import src.db.Database;
+
+public abstract class Model {
+    protected Connection conn;
+
+    public Model() {
+        try {
+            this.conn = Database.getConnection();
+        } catch (java.sql.SQLException e) {
+            throw new RuntimeException("Failed to get DB connection", e);
+        }
+    }
+}