// Deliberately minimal: fetch the raw VERSION file from `main` on GitHub
// and compare semver to the bundled version. No silent binary-replacing
// auto-update — that needs signing/notarization/an appcast server this
// project doesn't have. A manual check shows an alert (an explicit action
// that expects a response); the periodic automatic check instead posts a
// quiet system notification, since that one wasn't asked for in the
// moment.
import Foundation
import UserNotifications

enum UpdateChecker {
    enum Outcome {
        case upToDate
        case updateAvailable(version: String, url: URL)
        case failed
    }

    private static let versionURL = URL(string: "https://raw.githubusercontent.com/bdeshi/shannoncoat/main/VERSION")!
    private static let releaseURL = URL(string: "https://github.com/bdeshi/shannoncoat/releases/latest")!
    private static let enabledDefaultsKey = "AutomaticUpdateCheckEnabled"
    private static let lastCheckDefaultsKey = "LastUpdateCheckDate"
    private static let checkInterval: TimeInterval = 24 * 60 * 60

    static var automaticCheckEnabled: Bool {
        get { UserDefaults.standard.object(forKey: enabledDefaultsKey) as? Bool ?? true }
        set { UserDefaults.standard.set(newValue, forKey: enabledDefaultsKey) }
    }

    static var currentVersion: String {
        guard let resourceURL = Bundle.main.resourceURL,
              let contents = try? String(contentsOf: resourceURL.appendingPathComponent("VERSION"), encoding: .utf8)
        else { return "unknown" }
        return contents.trimmingCharacters(in: .whitespacesAndNewlines)
    }

    // What the About panel shows: the version alone for a real release
    // build (COMMIT is written empty when build.sh finds HEAD sitting
    // exactly on a tag), or version + short SHA for a dev build, so two
    // local builds off the same version number are distinguishable.
    static var displayVersion: String {
        commitSHA.isEmpty ? currentVersion : "\(currentVersion) (\(commitSHA))"
    }

    private static var commitSHA: String {
        guard let resourceURL = Bundle.main.resourceURL,
              let contents = try? String(contentsOf: resourceURL.appendingPathComponent("COMMIT"), encoding: .utf8)
        else { return "" }
        return contents.trimmingCharacters(in: .whitespacesAndNewlines)
    }

    static func checkManually(completion: @escaping (Outcome) -> Void) {
        fetchLatestVersion { latest in
            guard let latest else { completion(.failed); return }
            if isNewer(latest, than: currentVersion) {
                completion(.updateAvailable(version: latest, url: releaseURL))
            } else {
                completion(.upToDate)
            }
        }
    }

    // Called once at launch; a no-op unless the toggle is on and it's been
    // at least a day since the last check.
    static func checkAutomaticallyIfDue() {
        guard automaticCheckEnabled else { return }
        let last = UserDefaults.standard.object(forKey: lastCheckDefaultsKey) as? Date ?? .distantPast
        guard Date().timeIntervalSince(last) > checkInterval else { return }
        UserDefaults.standard.set(Date(), forKey: lastCheckDefaultsKey)

        fetchLatestVersion { latest in
            guard let latest, isNewer(latest, than: currentVersion) else { return }
            postAvailableNotification(version: latest)
        }
    }

    private static func fetchLatestVersion(completion: @escaping (String?) -> Void) {
        URLSession.shared.dataTask(with: versionURL) { data, _, _ in
            let version = data.flatMap { String(data: $0, encoding: .utf8) }?
                .trimmingCharacters(in: .whitespacesAndNewlines)
            completion((version?.isEmpty == false) ? version : nil)
        }.resume()
    }

    private static func isNewer(_ a: String, than b: String) -> Bool {
        let av = a.split(separator: ".").compactMap { Int($0) }
        let bv = b.split(separator: ".").compactMap { Int($0) }
        for i in 0..<max(av.count, bv.count) {
            let x = i < av.count ? av[i] : 0
            let y = i < bv.count ? bv[i] : 0
            if x != y { return x > y }
        }
        return false
    }

    private static func postAvailableNotification(version: String) {
        let center = UNUserNotificationCenter.current()
        center.requestAuthorization(options: [.alert]) { granted, _ in
            guard granted else { return }
            let content = UNMutableNotificationContent()
            content.title = "shannoncoat \(version) is available"
            content.body = "Click to view the release notes."
            center.add(UNNotificationRequest(identifier: "shannoncoat-update-available", content: content, trigger: nil))
        }
    }
}