//
//  EphemeralPreferenceStore.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
//

/// An ordered in-memory preference backend for tests and persistence fallback.
package actor EphemeralPreferenceStore: PreferenceStoring {
    package nonisolated let initialSnapshot: [String: StoredPreference]
    private var values: [String: StoredPreference]
    private nonisolated let continuation: AsyncStream<PreferenceWrite>.Continuation

    /// Creates an in-memory store seeded with optional raw values.
    ///
    /// - Parameter initialSnapshot: Values available before the first write.
    package init(initialSnapshot: [String: StoredPreference] = [:]) {
        self.initialSnapshot = initialSnapshot
        values = initialSnapshot
        let (stream, continuation) = AsyncStream<PreferenceWrite>.makeStream(bufferingPolicy: .unbounded)
        self.continuation = continuation
        Task { [weak self] in
            for await write in stream {
                guard let self else { break }
                await self.apply(write)
            }
        }
    }

    deinit {
        continuation.finish()
    }

    /// Queues a value update or deletion without blocking the caller.
    package nonisolated func enqueue(_ key: String, _ value: StoredPreference?) {
        continuation.yield(.set(key: key, value: value))
    }

    /// Returns after queued writes have been applied to the in-memory values.
    ///
    /// - Throws: Never; the in-memory backend has no write failure mode.
    package nonisolated func flush() async throws {
        try await withCheckedThrowingContinuation { (continuation: CheckedContinuation<Void, any Error>) in
            self.continuation.yield(
                .barrier { error in
                    if let error {
                        continuation.resume(throwing: error)
                    } else {
                        continuation.resume(returning: ())
                    }
                })
        }
    }

    /// The values currently held, for assertions.
    package var storedValues: [String: StoredPreference] { values }

    private func apply(_ write: PreferenceWrite) {
        switch write {
        case .set(let key, let value):
            if let value {
                values[key] = value
            } else {
                values.removeValue(forKey: key)
            }
        case .barrier(let resume):
            resume(nil)
        }
    }
}