import Foundation

struct PlaybackProgress {
    private let defaults: UserDefaults

    init(defaults: UserDefaults = .standard) {
        self.defaults = defaults
        // Migrate the old shared dictionary once; separate keys prevent cross-player lost updates.
        if let positions = defaults.dictionary(forKey: "playbackPositions") as? [String: Double] {
            for (identity, position) in positions where position.isFinite && position > 0 {
                let key = "playbackPosition:" + identity
                if defaults.object(forKey: key) == nil { defaults.set(position, forKey: key) }
            }
            defaults.removeObject(forKey: "playbackPositions")
        }
    }

    func position(for url: URL) -> Double? {
        guard let position = defaults.object(forKey: key(for: url)) as? Double,
              position.isFinite, position > 0 else { return nil }
        return position
    }

    func save(_ position: Double?, for url: URL) {
        let key = key(for: url)
        let position = position.flatMap { $0.isFinite && $0 > 0 ? $0 : nil }
        guard (defaults.object(forKey: key) as? Double) != position else { return }
        defaults.set(position, forKey: key)
    }

    private func key(for url: URL) -> String {
        // YouTube callers supply the canonical webpage URL, never an expiring media URL.
        return "playbackPosition:" + (url.isFileURL ? url.standardizedFileURL.resolvingSymlinksInPath().absoluteString : url.absoluteString)
    }
}