// StoryStore.swift
// Jarvis — central observable store. Views read from here, never hit the API directly.

import Foundation
import Combine
import SwiftData

@MainActor
final class StoryStore: ObservableObject {
    static let shared = StoryStore()

    @Published var stories: [StorySummary] = []
    @Published var isLoading = false
    @Published var isLoadingMore = false
    @Published var error: APIError?
    @Published var lastSyncedAt: Date?
    @Published var hasMore = false
    @Published var selectedTopic: String? = nil
    @Published var selectedTags: Set<String> = []
    @Published var sectionSupplement: [String: [StorySummary]] = [:]

    private var nextCursor: String?
    private var refreshTask: Task<Void, Never>?
    private var foregroundSyncTask: Task<Void, Never>?
    private var cancellables = Set<AnyCancellable>()

    // MARK: - Quick cache (UserDefaults — synchronous, no async gap)

    private let quickCacheKey = "jarvis.quickStories.v1"
    private let quickCacheMaxAge: TimeInterval = 84 * 3600  // 3.5 days

    /// Restore the last-known feed from UserDefaults synchronously on init.
    /// This runs before the first SwiftUI render so the feed is never blank.
    private func restoreQuickCache() {
        guard let raw = UserDefaults.standard.data(forKey: quickCacheKey) else { return }
        let decoder = JSONDecoder()
        decoder.dateDecodingStrategy = .iso8601
        guard let payload = try? decoder.decode(QuickCachePayload.self, from: raw) else { return }
        // Discard if too stale — matches CacheMaintenance window.
        guard Date().timeIntervalSince(payload.savedAt) < quickCacheMaxAge else {
            UserDefaults.standard.removeObject(forKey: quickCacheKey)
            return
        }
        if !payload.stories.isEmpty { stories = payload.stories }
    }

    /// Persist the current feed to UserDefaults so it survives process kills.
    private func persistQuickCache() {
        let encoder = JSONEncoder()
        encoder.dateEncodingStrategy = .iso8601
        let payload = QuickCachePayload(stories: Array(stories.prefix(100)), savedAt: Date())
        if let data = try? encoder.encode(payload) {
            UserDefaults.standard.set(data, forKey: quickCacheKey)
        }
    }

    private struct QuickCachePayload: Codable {
        let stories: [StorySummary]
        let savedAt: Date
    }

    // MARK: - SwiftData bootstrap (secondary, async — covers first-ever launch before
    // the quick cache exists, e.g. app reinstall).
    func bootstrap(container: ModelContainer) {
        guard stories.isEmpty else { return }
        let ctx = ModelContext(container)
        if let cached = try? ctx.fetch(FetchDescriptor<CachedStory>()) {
            let sorted = cached.map(StorySummary.init(cached:)).sorted(by: StorySummary.feedOrder)
            if !sorted.isEmpty { stories = sorted }
        }
    }

    // MARK: - Foreground sync

    private var isFetchingFull = false

    /// Load page 1 then paginate to ≤100 stories.
    /// Guarded against concurrent invocations and rate-limited to ≥30 s between
    /// fetches so rapid foreground/background cycles don't hammer the API.
    func loadFeedFull() async {
        guard !isFetchingFull else { return }
        // Rate-limit: if the last *successful* sync was < 30 s ago, skip.
        if let last = lastSyncedAt, Date().timeIntervalSince(last) < 30 { return }
        isFetchingFull = true
        defer { isFetchingFull = false }

        await loadStories(refresh: true)
        var pages = 0
        while !Task.isCancelled, hasMore, stories.count < 100, pages < 4 {
            await loadMore()
            pages += 1
        }
        loadSectionSupplements()
    }

    /// Call when app becomes active. Polls every 90 s so new stories surface fast.
    func startForegroundSync() {
        foregroundSyncTask?.cancel()
        foregroundSyncTask = Task { [weak self] in
            while !Task.isCancelled {
                try? await Task.sleep(nanoseconds: 90 * 1_000_000_000)
                guard !Task.isCancelled else { return }
                await self?.loadFeedFull()
            }
        }
    }

    func stopForegroundSync() {
        foregroundSyncTask?.cancel()
        foregroundSyncTask = nil
    }
    private let ws = WebSocketManager.shared
    private let api = APIClient.shared

    private init() {
        restoreQuickCache()   // synchronous — stories are ready before first render
        subscribeToWebSocket()
    }

    // MARK: - Load

    @discardableResult
    func loadStories(refresh: Bool = false) async -> Int {
        guard !isLoading else { return 0 }
        isLoading = true
        error = nil

        let cursor = refresh ? nil : nextCursor
        var newCount = 0

        do {
            let result = try await api.fetchStories(
                cursor: cursor,
                topic: selectedTopic,
                tags: selectedTags
            )
            if refresh {
                // Replace list; count only genuinely new IDs for reshuffle logic.
                let existingIds = Set(stories.map(\.id))
                newCount = result.data.filter { !existingIds.contains($0.id) }.count
                stories = result.data
            } else {
                // Append only IDs not already present — cursor can overlap.
                let existingIds = Set(stories.map(\.id))
                let novel = result.data.filter { !existingIds.contains($0.id) }
                stories += novel
                newCount = novel.count
            }
            nextCursor = result.nextCursor
            hasMore = result.hasMore
            lastSyncedAt = Date()
            persistQuickCache()          // survives the next process kill
            preCacheArticlesInBackground()
        } catch let e as APIError where !e.isCancelled {
            error = e
            print("[StoryStore] fetch failed: \(e.localizedDescription)")
        } catch {
            print("[StoryStore] unexpected fetch error: \(error)")
        }

        isLoading = false
        return newCount
    }

    private func preCacheArticlesInBackground() {
        guard let container = BackgroundRefreshManager.container else { return }
        let snapshot = stories
        Task.detached { await BackgroundRefreshManager.preCacheArticles(snapshot, container: container) }
    }

    /// Merge cached stories into the live feed (used when pull-refresh finds nothing new).
    func mergeStories(_ extra: [StorySummary]) async {
        let existing = Set(stories.map(\.id))
        let novel = extra.filter { !existing.contains($0.id) }
        guard !novel.isEmpty else { return }
        stories = (stories + novel).sorted(by: StorySummary.feedOrder)
    }

    func loadMore() async {
        guard hasMore, !isLoadingMore, let cursor = nextCursor else { return }
        isLoadingMore = true
        do {
            let result = try await api.fetchStories(cursor: cursor, topic: selectedTopic, tags: selectedTags)
            // Deduplicate: cursor-based pages can overlap when stories are added mid-fetch.
            let existingIds = Set(stories.map(\.id))
            let novel = result.data.filter { !existingIds.contains($0.id) }
            stories += novel
            nextCursor = result.nextCursor
            hasMore = result.hasMore
        } catch {
            print("[StoryStore] loadMore error: \(error)")
        }
        isLoadingMore = false
    }

    /// Coalesce bursts of `story.created` WS events — waits 3 s then does a
    /// full paginated load so stories on page 2+ are captured.
    private func scheduleCoalescedRefresh() {
        refreshTask?.cancel()
        refreshTask = Task { [weak self] in
            try? await Task.sleep(nanoseconds: 3_000_000_000)
            guard !Task.isCancelled else { return }
            await self?.loadFeedFull()
        }
    }

    // MARK: - Section supplements
    // Sections with regional or niche tags rarely rank in the global top-100,
    // so we fetch a small targeted pool for each sparse section and let
    // makeDigest() use it as a fallback.

    private let supplementSections: [(id: String, tags: Set<String>)] = [
        ("east-africa", ["east-africa"]),
        ("africa",      ["africa"]),
        ("sport",       ["sports", "esports", "formula-1"]),
        ("science",     ["science", "astronomy"]),
        ("health",      ["health", "health-and-wellness"]),
    ]

    func loadSectionSupplements() {
        guard selectedTags.isEmpty else { return }   // only for "All" pill
        for sec in supplementSections {
            let id = sec.id
            let tags = sec.tags
            Task { [weak self] in
                guard let self else { return }
                if let result = try? await api.fetchStories(tags: tags, limit: 8) {
                    await MainActor.run { self.sectionSupplement[id] = result.data }
                }
            }
        }
    }

    func setTopic(_ topic: String?) async {
        selectedTopic = topic
        selectedTags = []
        await loadFeedFull()
    }

    func setPill(_ pill: StoryPill) async {
        selectedTopic = nil
        selectedTags = pill.slugs
        nextCursor = nil
        // Filter changed — must fetch regardless of rate-limit, otherwise
        // the old stories stay in place and the new pill finds almost nothing.
        lastSyncedAt = nil
        await loadFeedFull()
    }

    // MARK: - WebSocket

    private func subscribeToWebSocket() {
        ws.events
            .receive(on: DispatchQueue.main)
            .sink { [weak self] event in
                self?.handle(event: event)
            }
            .store(in: &cancellables)
    }

    private func handle(event: WSEvent) {
        switch event.type {

        case .storyUpdated:
            guard let id = event.storyId,
                  let score = event.signalScore,
                  let count = event.sourceCount else { return }
            updateStory(id: id, signalScore: score, sourceCount: count)
            Task { await refetch(storyId: id) }

        case .storyCreated:
            scheduleCoalescedRefresh()

        case .storyStale:
            guard let id = event.storyId else { return }
            removeStory(id: id)

        case .feedHealth:
            NotificationCenter.default.post(name: .feedHealthChanged, object: event)

        default:
            break
        }
    }

    private func updateStory(id: String, signalScore: Int, sourceCount: Int) {
        guard let idx = stories.firstIndex(where: { $0.id == id }) else { return }
        let old = stories[idx]
        let updated = StorySummary(
            id: old.id,
            headline: old.headline,
            summary: old.summary,
            topic: old.topic,
            tags: old.tags,
            signalScore: signalScore,
            scoreBreakdown: old.scoreBreakdown,
            sourceCount: sourceCount,
            sources: old.sources,
            consensus: old.consensus,
            conflict: old.conflict,
            updatedAt: old.updatedAt,
            createdAt: old.createdAt
        )
        stories[idx] = updated
        stories.sort(by: StorySummary.feedOrder)
    }

    private func removeStory(id: String) {
        stories.removeAll { $0.id == id }
    }

    private func refetch(storyId: String) async {
        // Lightweight: only update what changed via WS patch above.
        // Full detail is fetched lazily when user taps into the story.
    }
}

extension Notification.Name {
    static let feedHealthChanged = Notification.Name("feedHealthChanged")
}