import Foundation

protocol Metadata: Codable {

    static var fileName: String { get }

    static var initial: Self { get }
}

extension Metadata {

    static func url(in folder: URL) -> URL {
        folder.appendingPathComponent(fileName)
    }

    static func exists(in folder: URL) -> Bool {
        url(in: folder).exists
    }

    init?(in folder: URL) throws {
        let metadataUrl = Self.url(in: folder)
        guard metadataUrl.exists else {
            try Self.initial.writeJSON(to: metadataUrl)
            print("Created metadata in \(folder)")
            return nil
        }
        try self.init(decodeFrom: metadataUrl)
    }
}