import Foundation

struct PlaybackProgress {
    private let defaults: UserDefaults
    private var positions: [String: Double]

    init(defaults: UserDefaults = .standard) {
        self.defaults = defaults
        positions = defaults.dictionary(forKey: "playbackPositions") as? [String: Double] ?? [:]
    }

    func position(for url: URL) -> Double? {
        guard let position = positions[key(for: url)], position.isFinite, position > 0 else { return nil }
        return position
    }

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

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