Improved type safety, local auth support, and better error handling

Sources/KeychainKit/Protocols/KeychainStorageProtocol.swift

@@ -0,0 +1,124 @@
+import Foundation
+
+/// A protocol that defines a type-safe interface for storing and retrieving values
+/// in the system keychain.
+///
+/// This protocol provides generic support for `Data`, `String`, `UUID`, and `Codable` types.
+/// It allows configuring the associated account and service context for each operation.
+///
+/// Types conforming to this protocol must specify concrete types for `Account`
+/// and `Service`, which describe keychain item identity and service grouping.
+///
+/// ## Topics
+///
+/// ### Associated Types
+///
+/// - ``Account``
+/// - ``Service``
+///
+/// ### Instance Properties
+///
+/// - ``service``
+///
+/// ### Retrieving Values
+///
+/// - ``get(_:)-2gcee``
+/// - ``get(_:)-23z7h``
+/// - ``get(_:)-4xbe6``
+/// - ``get(_:decoder:)``
+///
+/// ### Storing Values
+///
+/// - ``set(_:for:)-21dla``
+/// - ``set(_:for:)-6nzkf``
+/// - ``set(_:for:)-2smpc``
+/// - ``set(_:for:encoder:)``
+///
+/// ### Deleting Values
+///
+/// - ``delete(_:)``
+public protocol KeychainStorageProtocol {
+    /// A type that describes a keychain account and its security configuration.
+    associatedtype Account: KeychainAccountProtocol
+    
+    /// A type that identifies a keychain service context (e.g., app or subsystem).
+    associatedtype Service: KeychainServiceProtocol
+    
+    /// The service associated with this keychain storage instance.
+    ///
+    /// This value is used as the `kSecAttrService` when interacting with the keychain.
+    /// If `nil`, the default service behavior is used.
+    var service: Service? { get }
+    
+    /// Retrieves the value stored in the keychain for the specified account as raw `Data`.
+    ///
+    /// - Parameter account: The keychain account whose value should be retrieved.
+    /// - Returns: The data associated with the given account.
+    /// - Throws: An error if the item is not found, access is denied, or another keychain error occurs.
+    func get(_ account: Account) throws(KeychainError) -> Data
+    
+    /// Retrieves the value stored in the keychain for the specified account as a UTF-8 string.
+    ///
+    /// - Parameter account: The keychain account whose value should be retrieved.
+    /// - Returns: A string decoded from the stored data using UTF-8 encoding.
+    /// - Throws: An error if the item is not found, the data is not valid UTF-8,
+    ///   or a keychain access error occurs.
+    func get(_ account: Account) throws(KeychainError) -> String
+    
+    /// Retrieves the value stored in the keychain for the specified account as a `UUID`.
+    ///
+    /// - Parameter account: The keychain account whose value should be retrieved.
+    /// - Returns: A UUID decoded from a 16-byte binary representation stored in the keychain.
+    /// - Throws: An error if the item is not found, the data is not exactly 16 bytes,
+    ///   or a keychain access error occurs.
+    func get(_ account: Account) throws(KeychainError) -> UUID
+    
+    /// Retrieves and decodes a value of type `T` stored in the keychain for the specified account.
+    ///
+    /// - Parameters:
+    ///   - account: The keychain account whose value should be retrieved.
+    ///   - decoder: The `JSONDecoder` instance used to decode the stored data.
+    /// - Returns: A decoded instance of type `T`.
+    /// - Throws: An error if the item is not found, decoding fails, or a keychain access error occurs.
+    func get<T: Decodable>(_ account: Account, decoder: JSONDecoder) throws(KeychainError) -> T
+    
+    /// Stores raw `Data` in the keychain for the specified account.
+    ///
+    /// - Parameters:
+    ///   - value: The data to store in the keychain.
+    ///   - account: The keychain account under which the data will be saved.
+    /// - Throws: An error if storing the data fails.
+    func set(_ value: Data, for account: Account) throws(KeychainError)
+    
+    /// Stores a UTF-8 encoded `String` in the keychain for the specified account.
+    ///
+    /// - Parameters:
+    ///   - value: The string to store in the keychain.
+    ///   - account: The keychain account under which the string will be saved.
+    /// - Throws: An error if storing the string fails.
+    func set(_ value: String, for account: Account) throws(KeychainError)
+    
+    /// Stores a `UUID` in the keychain for the specified account.
+    ///
+    /// - Parameters:
+    ///   - value: The UUID to store in the keychain (stored in 16-byte binary format).
+    ///   - account: The keychain account under which the UUID will be saved.
+    /// - Throws: An error if storing the UUID fails.
+    func set(_ value: UUID, for account: Account) throws(KeychainError)
+    
+    /// Encodes and stores a value of type `T` in the keychain for the specified account.
+    ///
+    /// - Parameters:
+    ///   - value: The value to encode and store.
+    ///   - account: The keychain account under which the encoded data will be saved.
+    ///   - encoder: The `JSONEncoder` used to encode the value.
+    /// - Throws: An error if encoding or storing the value fails.
+    func set<T: Encodable>(_ value: T, for account: Account, encoder: JSONEncoder) throws(KeychainError)
+    
+    /// Deletes the keychain item associated with the specified account.
+    ///
+    /// - Parameter account: The keychain account whose stored value should be deleted.
+    /// - Note: If the item does not exist, the method completes silently without error.
+    /// - Throws: An error only if the item exists but removal fails.
+    func delete(_ account: Account) throws(KeychainError)
+}