252 lines
11 KiB
Swift
252 lines
11 KiB
Swift
import Foundation
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import DataLiteCore
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import DataLiteC
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/// A base class for services that operate on a database connection.
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///
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/// `DatabaseService` provides a shared interface for executing operations on a `Connection`,
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/// with support for transaction handling and optional request serialization.
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///
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/// Subclasses can use this base to coordinate safe, synchronous access to the database
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/// without duplicating concurrency or transaction logic.
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///
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/// For example, you can define a custom service for managing notes:
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///
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/// ```swift
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/// final class NoteService: DatabaseService {
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/// func insertNote(_ text: String) throws {
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/// try perform { connection in
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/// let stmt = try connection.prepare(
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/// sql: "INSERT INTO notes (text) VALUES (?)"
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/// )
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/// try stmt.bind(text, at: 0)
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/// try stmt.step()
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/// }
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/// }
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///
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/// func fetchNotes() throws -> [String] {
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/// try perform { connection in
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/// let stmt = try connection.prepare(sql: "SELECT text FROM notes")
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/// var result: [String] = []
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/// while try stmt.step() {
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/// if let text: String = stmt.columnValue(at: 0) {
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/// result.append(text)
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/// }
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/// }
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/// return result
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/// }
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/// }
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/// }
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///
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/// let connection = try Connection(location: .inMemory, options: .readwrite)
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/// let service = NoteService(connection: connection)
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///
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/// try service.insertNote("Hello, world!")
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/// let notes = try service.fetchNotes()
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/// print(notes) // ["Hello, world!"]
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/// ```
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///
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/// This approach allows you to build reusable service layers on top of a safe, transactional,
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/// and serialized foundation.
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open class DatabaseService: DatabaseServiceProtocol {
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/// A closure that provides a new database connection when invoked.
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///
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/// `ConnectionProvider` is used to defer the creation of a `Connection` instance
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/// until it is actually needed. It can throw errors if the connection cannot be
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/// established or configured correctly.
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///
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/// - Returns: A valid `Connection` instance.
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/// - Throws: Any error encountered while opening or configuring the connection.
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public typealias ConnectionProvider = () throws -> Connection
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// MARK: - Properties
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private let provider: ConnectionProvider
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private var connection: Connection
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private let queue: DispatchQueue
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private let queueKey = DispatchSpecificKey<Void>()
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/// The object that provides the encryption key for the database connection.
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///
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/// When this property is set, the service attempts to retrieve an encryption key from the
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/// provider and apply it to the current database connection. This operation is performed
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/// synchronously on the service’s internal queue to ensure thread safety.
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///
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/// If an error occurs during key retrieval or application, the service notifies the provider
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/// by calling `databaseService(_:didReceive:)`.
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///
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/// This enables external management of encryption keys, including features such as key rotation,
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/// user-scoped encryption, or error handling delegation.
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///
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/// - Important: The service does not retry failed key applications. Ensure the provider is
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/// correctly configured and able to supply a valid key when needed.
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public weak var keyProvider: DatabaseServiceKeyProvider? {
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didSet {
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perform { connection in
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do {
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if let key = try keyProvider?.databaseServiceKey(self) {
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try connection.apply(key)
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}
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} catch {
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keyProvider?.databaseService(self, didReceive: error)
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}
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}
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}
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}
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// MARK: - Inits
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/// Creates a new `DatabaseService` using the given connection provider and optional queue.
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///
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/// This convenience initializer wraps the provided autoclosure in a `ConnectionProvider`
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/// and delegates to the designated initializer. It is useful when passing a simple
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/// connection expression.
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///
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/// - Parameters:
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/// - provider: A closure that returns a `Connection` instance and may throw.
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/// - queue: An optional dispatch queue used as a target for internal serialization. If `nil`,
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/// a default serial queue with `.utility` QoS is created internally.
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/// - Throws: Rethrows any error thrown by the connection provider.
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public convenience init(
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connection provider: @escaping @autoclosure ConnectionProvider,
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queue: DispatchQueue? = nil
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) rethrows {
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try self.init(provider: provider, queue: queue)
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}
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/// Creates a new `DatabaseService` with the specified connection provider and dispatch queue.
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///
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/// This initializer immediately invokes the `provider` closure to establish the initial database
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/// connection. An internal serial queue is created for synchronizing database access. If a
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/// `queue` is provided, it is set as the target of the internal queue, allowing you to control
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/// scheduling and quality of service.
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///
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/// - Parameters:
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/// - provider: A closure that returns a new `Connection` instance. May throw on failure.
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/// - queue: An optional dispatch queue to target for internal serialization. If `nil`,
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/// a dedicated serial queue with `.utility` QoS is created.
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/// - Throws: Any error thrown by the `provider` during initial connection setup.
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public init(
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provider: @escaping ConnectionProvider,
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queue: DispatchQueue? = nil
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) rethrows {
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self.provider = provider
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self.connection = try provider()
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self.queue = .init(for: Self.self, qos: .utility)
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self.queue.setSpecific(key: queueKey, value: ())
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if let queue = queue {
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self.queue.setTarget(queue: queue)
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}
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}
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// MARK: - Methods
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/// Re-establishes the database connection using the stored connection provider.
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///
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/// This method creates a new `Connection` instance by invoking the original provider. If a
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/// `keyProvider` is set, the method attempts to retrieve and apply an encryption key to the new
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/// connection. The new connection replaces the existing one.
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///
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/// The operation is executed synchronously on the internal dispatch queue via `perform(_:)`
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/// to ensure thread safety.
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///
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/// - Throws: Any error thrown during connection creation or while retrieving or applying the
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/// encryption key.
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public func reconnect() throws {
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try perform { _ in
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let connection = try provider()
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if let key = try keyProvider?.databaseServiceKey(self) {
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try connection.apply(key)
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}
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self.connection = connection
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}
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}
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/// Executes the given closure using the active database connection.
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///
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/// This method ensures thread-safe access to the underlying `Connection` by synchronizing
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/// execution on an internal serial dispatch queue. If the call is already on that queue, the
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/// closure is executed directly to avoid unnecessary dispatching.
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///
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/// If the closure throws a `SQLiteError` with code `SQLITE_NOTADB` (e.g., when the database file
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/// is corrupted or invalid), the service attempts to re-establish the connection by calling
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/// ``reconnect()``. The error is still rethrown after reconnection.
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///
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/// - Parameter closure: A closure that takes the active connection and returns a result.
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/// - Returns: The value returned by the closure.
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/// - Throws: Any error thrown by the closure or during reconnection logic.
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public func perform<T>(_ closure: Perform<T>) rethrows -> T {
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do {
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switch DispatchQueue.getSpecific(key: queueKey) {
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case .none: return try queue.asyncAndWait { try closure(connection) }
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case .some: return try closure(connection)
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}
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} catch {
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switch error {
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case let error as Connection.Error:
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if error.code == SQLITE_NOTADB {
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try reconnect()
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}
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fallthrough
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default:
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throw error
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}
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}
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}
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/// Executes a closure inside a transaction if the connection is in autocommit mode.
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///
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/// If the current connection is in autocommit mode, a new transaction of the specified type
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/// is started, and the closure is executed within it. If the closure completes successfully,
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/// the transaction is committed. If an error is thrown, the transaction is rolled back.
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///
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/// If the thrown error is a `SQLiteError` with code `SQLITE_NOTADB`, the service attempts to
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/// reconnect and retries the entire transaction block exactly once.
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///
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/// If the connection is already within a transaction (i.e., not in autocommit mode),
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/// the closure is executed directly without starting a new transaction.
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///
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/// - Parameters:
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/// - transaction: The type of transaction to begin (e.g., `deferred`, `immediate`, `exclusive`).
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/// - closure: A closure that takes the active connection and returns a result.
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/// - Returns: The value returned by the closure.
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/// - Throws: Any error thrown by the closure, transaction control statements,
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/// or reconnect logic.
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public func perform<T>(
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in transaction: TransactionType,
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closure: Perform<T>
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) rethrows -> T {
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if connection.isAutocommit {
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try perform { connection in
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do {
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try connection.beginTransaction(transaction)
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let result = try closure(connection)
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try connection.commitTransaction()
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return result
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} catch {
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try connection.rollbackTransaction()
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guard let error = error as? Connection.Error,
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error.code == SQLITE_NOTADB
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else { throw error }
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try reconnect()
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return try perform { connection in
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do {
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try connection.beginTransaction(transaction)
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let result = try closure(connection)
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try connection.commitTransaction()
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return result
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} catch {
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try connection.rollbackTransaction()
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throw error
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}
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}
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}
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}
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} else {
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try perform(closure)
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}
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}
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}
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