import Combine
import Disk
import Foundation

protocol FileStorage {
    func save<Value: JSON>(_: Value, as name: String) -> AnyPublisher<Void, Error>
    func retrieve<Value: JSON>(_: String, as type: Value.Type) -> AnyPublisher<Value, Error>
    func append<Value: JSON>(_: Value, to name: String) -> AnyPublisher<Void, Error>
}

final class BaseFileStorage: FileStorage {
    private let processQueue = DispatchQueue(label: "BaseFileStorage.processQueue")

    func save<Value: JSON>(_ value: Value, as name: String) -> AnyPublisher<Void, Error> {
        Future { promise in
            self.processQueue.async {
                do {
                    let encoder = JSONEncoder()
                    encoder.outputFormatting = .prettyPrinted
                    try Disk.save(value, to: .documents, as: name, encoder: encoder)
                    promise(.success(()))
                } catch {
                    promise(.failure(error))
                }
            }
        }
        .eraseToAnyPublisher()
    }

    func retrieve<Value: JSON>(_ name: String, as type: Value.Type) -> AnyPublisher<Value, Error> {
        Future { promise in
            self.processQueue.async {
                do {
                    let value = try Disk.retrieve(name, from: .documents, as: type)
                    promise(.success(value))
                } catch {
                    promise(.failure(error))
                }
            }
        }
        .eraseToAnyPublisher()
    }

    func append<Value: JSON>(_ newValue: Value, to name: String) -> AnyPublisher<Void, Error> {
        Future { promise in
            self.processQueue.async {
                do {
                    try Disk.append(newValue, to: name, in: .documents)
                    promise(.success(()))
                } catch {
                    promise(.failure(error))
                }
            }
        }
        .eraseToAnyPublisher()
    }
}