import Foundation

/// The default app storage provider for apps which don't specify a
/// custom one.
///
/// This uses `UserDefaults` on all platforms.
public typealias DefaultAppStorageProvider = UserDefaultsAppStorageProvider

/// A type that can be used to persist ``AppStorage`` values to disk.
public protocol AppStorageProvider: Sendable {
    /// Persists the given value.
    ///
    /// - Parameters:
    ///   - value: The value to persist.
    ///   - key: The key to assign the value to.
    func persistValue<Value: Codable>(_ value: Value, forKey key: String) throws
    /// Retrieves the value for the given key.
    ///
    /// - Parameters:
    ///   - type: The type that you expect the value to be.
    ///   - key: The key to retrieve the value from.
    /// - Returns: The persisted value for `key`, if it exists and is of the
    ///   expected type; otherwise, `nil`.
    func retrieveValue<Value: Codable>(ofType type: Value.Type, forKey key: String) -> Value?
}

/// A simple app storage provider that uses `UserDefaults` to persist
/// data.
///
/// This works on all supported platforms.
public struct UserDefaultsAppStorageProvider: AppStorageProvider {
    public func persistValue<Value: Codable>(_ value: Value, forKey key: String) throws {
        _ = try JSONEncoder().encode(value)
        // let jsonString = String(decoding: jsonData.bytes, as: UTF8.self)
        //UserDefaults.standard.set(jsonString, forKey: key)
    }

    public func retrieveValue<Value: Codable>(ofType: Value.Type, forKey key: String) -> Value? {
        return nil
    }
}

extension AppStorageProvider {
    public func getValue<T: Codable & Sendable>(key: String, defaultValue: T) -> T {
        // If this is the very first time we're reading from this key, it won't
        // be in the cache yet. In that case, we return the already-persisted value
        // if it exists, or the default value otherwise; either way, we add it to the
        // cache so subsequent accesses of `value` won't have to read from disk again.
        guard let cachedValue = appStorageCache[key] else {
            let value =
                self.retrieveValue(ofType: T.self, forKey: key) ?? defaultValue
            appStorageCache[key] = value
            return value
        }

        // Make sure that we have the right type.
        guard let typedValue = cachedValue as? T else {
            logger.warning(
                Logger.Message(stringLiteral: "'@AppStorage' property is of the wrong type; using default value"),
                metadata: [
                    "key": "\(key)",
                    "providedType": "\(T.self)",
                    "actualType": "\(type(of: cachedValue))",
                ]
            )
            return defaultValue
        }

        return typedValue
    }

    public func setValue<T: Codable & Sendable>(key: String, newValue: T) {
        appStorageCache[key] = newValue
        do {
            logger.trace(Logger.Message(stringLiteral: "persisting '\(newValue)' for '\(key)'"))
            try self.persistValue(newValue, forKey: key)
        } catch {
            logger.warning(
                Logger.Message(stringLiteral: "failed to encode '@AppStorage' data"),
                metadata: [
                    "value": "\(newValue)",
                    "error": "\(error.localizedDescription)",
                ]
            )
        }
    }
}