import Foundation
import Observation

enum AppLanguage: String, CaseIterable, Identifiable {
    case system
    case english
    case korean

    var id: String { rawValue }

    var displayName: String {
        switch self {
        case .system:  return String(localized: "settings.language.system")
        case .english: return "English"
        case .korean:  return "한국어"
        }
    }
}

enum FirstWeekday: Int, CaseIterable, Identifiable {
    case sunday = 1
    case monday = 2

    var id: Int { rawValue }

    var displayName: String {
        switch self {
        case .sunday: return String(localized: "settings.firstWeekday.sunday")
        case .monday: return String(localized: "settings.firstWeekday.monday")
        }
    }
}

@MainActor
@Observable
final class SettingsViewModel {
    private static let languageKey = "settings.language"
    private static let firstWeekdayKey = "settings.firstWeekday"
    private static let dayStartMinutesKey = "settings.dayStartMinutes"

    static let defaultDayStartMinutes = 4 * 60 // 04:00 AM

    var language: AppLanguage {
        didSet { UserDefaults.standard.set(language.rawValue, forKey: Self.languageKey) }
    }

    var firstWeekday: FirstWeekday {
        didSet { UserDefaults.standard.set(firstWeekday.rawValue, forKey: Self.firstWeekdayKey) }
    }

    /// Minutes since midnight marking when a "day" starts for goal/log purposes.
    var dayStartMinutes: Int {
        didSet { UserDefaults.standard.set(dayStartMinutes, forKey: Self.dayStartMinutesKey) }
    }

    var dayStartDate: Date {
        get {
            Calendar.current.date(bySettingHour: dayStartMinutes / 60, minute: dayStartMinutes % 60, second: 0, of: .now) ?? .now
        }
        set {
            let comps = Calendar.current.dateComponents([.hour, .minute], from: newValue)
            dayStartMinutes = (comps.hour ?? 0) * 60 + (comps.minute ?? 0)
        }
    }

    init() {
        let defaults = UserDefaults.standard
        language = AppLanguage(rawValue: defaults.string(forKey: Self.languageKey) ?? "") ?? .system
        firstWeekday = FirstWeekday(rawValue: defaults.integer(forKey: Self.firstWeekdayKey)) ?? .sunday
        if let storedMinutes = defaults.object(forKey: Self.dayStartMinutesKey) as? Int {
            dayStartMinutes = storedMinutes
        } else {
            dayStartMinutes = Self.defaultDayStartMinutes
        }
    }
}