import Foundation

struct Config {

    /// The port where the server runs
    let port: Int

    /// The name of the file in the `Resources` folder containing the device authentication token
    let keyFileName: String

    /// The seconds to wait for a response from the device
    let deviceTimeout: Int64

    /// The authentication tokens to use for monitoring of the service
    let authenticationTokens: Set<String>
    
    /// The path to the folder where the metric logs are stored
    ///
    /// If no path is provided, then a folder `logs` in the resources directory is created
    /// If the path is relative, then it is assumed relative to the resources directory
    let logPath: String?
    
    func logURL(possiblyRelativeTo resourcesDirectory: URL) -> URL {
        guard let logPath else {
            return resourcesDirectory.appendingPathComponent("logs")
        }
        guard !logPath.hasPrefix("/") else {
            return .init(fileURLWithPath: logPath)
        }
        return resourcesDirectory.appendingPathComponent(logPath)
    }
}

extension Config: Codable {

}

extension Config {

    init(loadFrom url: URL) throws {
        guard FileManager.default.fileExists(atPath: url.path) else {
            log("No configuration file found at \(url.path)")
            fatalError("No configuration file found")
        }
        let data: Data
        do {
            data = try Data(contentsOf: url)
        } catch {
            log("Failed to read config data: \(error)")
            throw error
        }
        do {
            self = try JSONDecoder().decode(Config.self, from: data)
        } catch {
               log("Failed to decode config data: \(error)")
               throw error
           }
    }
}