// BackgroundRefreshManager.swift
// Jarvis — background story cache refresh. Fires via BGAppRefreshTask every ~30 min,
// fetches the latest feed, and upserts CachedStory rows so the SwiftData cache is
// warm before the user opens the app.

import Foundation
import BackgroundTasks
import SwiftData

let jarvisFeedRefreshID = "com.kisani.jarvis.feed.refresh"

enum BackgroundRefreshManager {

    // Injected once from JarvisApp so the BG task can open a context on the same store.
    static var container: ModelContainer?

    // MARK: - Task handler

    static func handleFeedRefresh(task: BGAppRefreshTask) {
        // Reschedule first — if the task is killed we still get another run later.
        scheduleFeedRefresh()

        guard let container else {
            task.setTaskCompleted(success: false)
            return
        }

        let work = Task {
            await fetchAndCache(container: container)
        }

        task.expirationHandler = {
            work.cancel()
            task.setTaskCompleted(success: false)
        }

        Task {
            _ = await work.result
            task.setTaskCompleted(success: !work.isCancelled)
        }
    }

    // MARK: - Core fetch + upsert

    private static func fetchAndCache(container: ModelContainer) async {
        do {
            let page = try await APIClient.shared.fetchStories(limit: 40)
            let context = ModelContext(container)

            for story in page.data {
                let id = story.id
                if let existing = (try? context.fetch(
                    FetchDescriptor<CachedStory>(predicate: #Predicate { $0.id == id })))?.first {
                    // Refresh signal score and freshness on already-cached rows.
                    existing.signalScore = story.signalScore
                    existing.sourceCount = story.sourceCount
                    existing.updatedAt   = story.updatedAt
                } else {
                    context.insert(CachedStory(from: story))
                }
            }

            try? context.save()
        } catch {
            // Network unavailable in background — fail silently, next run will catch up.
        }
    }

    // MARK: - Schedule

    static func scheduleFeedRefresh() {
        let req = BGAppRefreshTaskRequest(identifier: jarvisFeedRefreshID)
        // iOS enforces a minimum interval (~15 min); 30 min is a reasonable target.
        req.earliestBeginDate = Date(timeIntervalSinceNow: 30 * 60)
        try? BGTaskScheduler.shared.submit(req)
    }
}