DomainCacheEngine.swift

//
//  DomainCacheEngine.swift
//  Data
//
//  Created by 박민서 on 3/20/26.
//  Copyright © 2025 yapp25thTeamTnT. All rights reserved.
//

import Foundation

enum DomainCacheReadResult<Snapshot: DomainCacheSnapshot>: Sendable {
    case fresh(Snapshot)
    case stale(Snapshot)
    case miss

    var freshSnapshot: Snapshot? {
        guard case .fresh(let snapshot) = self else { return nil }
        return snapshot
    }
}

actor DomainCacheEngine {
    private let policy: DomainCachePolicy
    private let storage: any DomainSnapshotStoring
    private let now: @Sendable () -> Date

    init(
        policy: DomainCachePolicy,
        storage: any DomainSnapshotStoring,
        now: @escaping @Sendable () -> Date = { Date() }
    ) {
        self.policy = policy
        self.storage = storage
        self.now = now
    }

    func loadSnapshot<Snapshot: DomainCacheSnapshot>(
        _ type: Snapshot.Type,
        key: DomainCacheKey,
        maxAge: TimeInterval?
    ) async throws -> DomainCacheReadResult<Snapshot> {
        guard let envelope: DomainCacheEnvelope<Snapshot> = try await storage.loadSnapshot(
            type,
            key: key,
            policy: policy
        ) else {
            return .miss
        }

        guard let maxAge else { return .fresh(envelope.snapshot) }
        return now().timeIntervalSince(envelope.savedAt) <= maxAge
            ? .fresh(envelope.snapshot)
            : .stale(envelope.snapshot)
    }

    func saveSnapshot<Snapshot: DomainCacheSnapshot>(
        _ snapshot: Snapshot,
        key: DomainCacheKey
    ) async throws {
        try await storage.saveSnapshot(snapshot, key: key, policy: policy)
        try await storage.cleanupSnapshots(namespace: key.namespace, policy: policy, now: now())
    }

    func clear(namespace: String) async throws {
        try await storage.removeSnapshots(namespace: namespace, policy: policy)
    }

    func cleanupSnapshotsAcrossNamespaces() async throws {
        try await storage.cleanupSnapshots(policy: policy, now: now())
    }
}