//
//  PreferenceSlot.swift
//
//  Copyright 2026 Brendan Szymanski <hello@bscubed.dev>
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program.  If not, see <https://www.gnu.org/licenses/>.
//
//  SPDX-License-Identifier: GPL-3.0-or-later
//

import LuminateCore
import Observation

/// The observable cell backing one preference key.
///
/// One instance per key lets Swift Observation track each preference independently.
@Observable @MainActor package final class PreferenceSlot<Value: PreferenceValue> {
    /// Invoked synchronously after every value write.
    @ObservationIgnored private let onChange: (Value?) -> Void

    /// The current value, or `nil` when the key has never been set.
    package var value: Value? {
        didSet { onChange(value) }
    }

    /// Creates a slot with an optional initial value and persistence hook.
    ///
    /// - Parameters:
    ///   - value: The value restored from storage, or `nil` when unset. Initialization does not
    ///     invoke `onChange`.
    ///   - onChange: Invoked synchronously after every subsequent value write.
    package init(_ value: Value?, onChange: @escaping (Value?) -> Void) {
        self.onChange = onChange
        self.value = value
    }
}