// CacheMaintenance.swift
// Jarvis — bounds the on-device SwiftData caches so they don't grow forever.
// Saved (bookmarked) stories are always protected.

import Foundation
import SwiftData

@MainActor
enum CacheMaintenance {
    private static let hour: TimeInterval = 3_600
    private static let day: TimeInterval = 86_400

    private static let recentHours = 84.0    // 3.5 days: survives weekends
    private static let markerHours = 96.0   // 4 days: active window + buffer
    private static let articleDays = 14.0    // cached article bodies (backend article retention)

    /// Age-based eviction. Run on launch. Cheap; protects saved stories.
    static func prune(_ context: ModelContext) {
        let now = Date()
        let seenCutoff = now.addingTimeInterval(-markerHours * hour)
        let readCutoff = now.addingTimeInterval(-markerHours * hour)
        let articleCutoff = now.addingTimeInterval(-articleDays * day)
        let storyCutoff = now.addingTimeInterval(-recentHours * hour)

        // Markers: simple age batch deletes.
        try? context.delete(model: SeenStory.self, where: #Predicate { $0.seenAt < seenCutoff })
        try? context.delete(model: ReadStory.self, where: #Predicate { $0.readAt < readCutoff })

        // Offline content: drop old entries that aren't saved.
        let saved = savedIDs(context)
        if let arts = try? context.fetch(
            FetchDescriptor<CachedArticle>(predicate: #Predicate { $0.cachedAt < articleCutoff })) {
            for a in arts where !saved.contains(a.storyId) { context.delete(a) }
        }
        if let stories = try? context.fetch(
            FetchDescriptor<CachedStory>(predicate: #Predicate { $0.cachedAt < storyCutoff })) {
            for s in stories where !saved.contains(s.id) { context.delete(s) }
        }
        try? context.save()
    }

    /// Manual "Clear cache" — wipes offline stories/articles + seen/read state,
    /// keeps your saved bookmarks (and their articles).
    static func clear(_ context: ModelContext) {
        try? context.delete(model: SeenStory.self)
        try? context.delete(model: ReadStory.self)
        let saved = savedIDs(context)
        if let arts = try? context.fetch(FetchDescriptor<CachedArticle>()) {
            for a in arts where !saved.contains(a.storyId) { context.delete(a) }
        }
        if let stories = try? context.fetch(FetchDescriptor<CachedStory>()) {
            for s in stories where !saved.contains(s.id) { context.delete(s) }
        }
        try? context.save()
    }

    private static func savedIDs(_ context: ModelContext) -> Set<String> {
        Set((try? context.fetch(FetchDescriptor<SavedStory>()))?.map(\.id) ?? [])
    }
}