// PostgreSQL Database Example
//
// Demonstrates the Postgres effect for database operations.
//
// Prerequisites:
//   - PostgreSQL server running locally
//   - Database 'testdb' created
//   - User 'testuser' with password 'testpass'
//
// To set up:
//   createdb testdb
//   psql testdb -c "CREATE TABLE users (id SERIAL PRIMARY KEY, name TEXT, email TEXT);"
//
// Run with: lux examples/postgres_demo.lux

// ============================================================
// Helper Functions
// ============================================================

fn jsonStr(key: String, value: String): String =
    "\"" + key + "\":\"" + value + "\""

fn jsonNum(key: String, value: Int): String =
    "\"" + key + "\":" + toString(value)

fn jsonObj(content: String): String =
    "{" + content + "}"

// ============================================================
// Database Operations
// ============================================================

// Insert a user
fn insertUser(connId: Int, name: String, email: String): Int with {Console, Postgres} = {
    let sql = "INSERT INTO users (name, email) VALUES ('" + name + "', '" + email + "') RETURNING id"
    Console.print("Inserting user: " + name)
    match Postgres.queryOne(connId, sql) {
        Some(row) => {
            Console.print("  Inserted with ID: " + toString(row.id))
            row.id
        },
        None => {
            Console.print("  Insert failed")
            -1
        }
    }
}

// Get all users
fn getUsers(connId: Int): Unit with {Console, Postgres} = {
    Console.print("Fetching all users...")
    let rows = Postgres.query(connId, "SELECT id, name, email FROM users ORDER BY id")
    Console.print("  Found " + toString(List.length(rows)) + " users:")
    List.forEach(rows, fn(row: { id: Int, name: String, email: String }): Unit with {Console} => {
        Console.print("    - " + toString(row.id) + ": " + row.name + " <" + row.email + ">")
    })
}

// Get user by ID
fn getUserById(connId: Int, id: Int): Unit with {Console, Postgres} = {
    let sql = "SELECT id, name, email FROM users WHERE id = " + toString(id)
    Console.print("Looking up user " + toString(id) + "...")
    match Postgres.queryOne(connId, sql) {
        Some(row) => Console.print("  Found: " + row.name + " <" + row.email + ">"),
        None => Console.print("  User not found")
    }
}

// Update user email
fn updateUserEmail(connId: Int, id: Int, newEmail: String): Unit with {Console, Postgres} = {
    let sql = "UPDATE users SET email = '" + newEmail + "' WHERE id = " + toString(id)
    Console.print("Updating user " + toString(id) + " email to " + newEmail)
    let affected = Postgres.execute(connId, sql)
    Console.print("  Rows affected: " + toString(affected))
}

// Delete user
fn deleteUser(connId: Int, id: Int): Unit with {Console, Postgres} = {
    let sql = "DELETE FROM users WHERE id = " + toString(id)
    Console.print("Deleting user " + toString(id))
    let affected = Postgres.execute(connId, sql)
    Console.print("  Rows affected: " + toString(affected))
}

// ============================================================
// Transaction Example
// ============================================================

fn transactionDemo(connId: Int): Unit with {Console, Postgres} = {
    Console.print("")
    Console.print("=== Transaction Demo ===")

    // Start transaction
    Console.print("Beginning transaction...")
    Postgres.beginTx(connId)

    // Make some changes
    insertUser(connId, "TxUser1", "tx1@example.com")
    insertUser(connId, "TxUser2", "tx2@example.com")

    // Show users before commit
    Console.print("Users before commit:")
    getUsers(connId)

    // Commit the transaction
    Console.print("Committing transaction...")
    Postgres.commit(connId)

    Console.print("Transaction committed!")
}

// ============================================================
// Main
// ============================================================

fn main(): Unit with {Console, Postgres} = {
    Console.print("========================================")
    Console.print("  PostgreSQL Demo")
    Console.print("========================================")
    Console.print("")

    // Connect to database
    Console.print("Connecting to PostgreSQL...")
    let connStr = "host=localhost user=testuser password=testpass dbname=testdb"
    let connId = Postgres.connect(connStr)
    Console.print("Connected! Connection ID: " + toString(connId))
    Console.print("")

    // Create table if not exists
    Console.print("Creating users table...")
    Postgres.execute(connId, "CREATE TABLE IF NOT EXISTS users (id SERIAL PRIMARY KEY, name TEXT NOT NULL, email TEXT NOT NULL)")
    Console.print("")

    // Clear table for demo
    Console.print("Clearing existing data...")
    Postgres.execute(connId, "DELETE FROM users")
    Console.print("")

    // Insert some users
    Console.print("=== Inserting Users ===")
    let id1 = insertUser(connId, "Alice", "alice@example.com")
    let id2 = insertUser(connId, "Bob", "bob@example.com")
    let id3 = insertUser(connId, "Charlie", "charlie@example.com")
    Console.print("")

    // Query all users
    Console.print("=== All Users ===")
    getUsers(connId)
    Console.print("")

    // Query single user
    Console.print("=== Single User Lookup ===")
    getUserById(connId, id2)
    Console.print("")

    // Update user
    Console.print("=== Update User ===")
    updateUserEmail(connId, id2, "bob.new@example.com")
    getUserById(connId, id2)
    Console.print("")

    // Delete user
    Console.print("=== Delete User ===")
    deleteUser(connId, id3)
    getUsers(connId)
    Console.print("")

    // Transaction demo
    transactionDemo(connId)
    Console.print("")

    // Final state
    Console.print("=== Final State ===")
    getUsers(connId)
    Console.print("")

    // Close connection
    Console.print("Closing connection...")
    Postgres.close(connId)
    Console.print("Done!")
}

// Note: This will fail if PostgreSQL is not running
// To test the syntax only, you can comment out the last line
let output = run main() with {}