import Foundation
import Observation
import OrgSocialKit

@Observable @MainActor
final class ProfileViewModel {

    struct FollowDetails: Equatable {
        let nick: String?
        let avatar: URL?
    }

    var profile: OrgSocialProfile?
    var isLoading = false
    var errorMessage: String?
    /// Nick + avatar fetched from each followed feed's own header. Populated
    /// asynchronously after the profile loads so rows fill in incrementally
    /// instead of all at once.
    var enrichedFollows: [URL: FollowDetails] = [:]

    private let fetcher = ProfileFetcher()
    private let feedURL: URL
    private var enrichTask: Task<Void, Never>?

    init(feedURL: URL) {
        self.feedURL = feedURL
    }

    func removePost(timestamp: String) {
        profile?.posts.removeAll { $0.timestamp == timestamp }
    }

    func updatePost(timestamp: String, newText: String) {
        guard let idx = profile?.posts.firstIndex(where: { $0.timestamp == timestamp }) else { return }
        profile?.posts[idx].text = newText
    }

    func applyEdit(timestamp: String, result: PostEditResult) {
        guard let idx = profile?.posts.firstIndex(where: { $0.timestamp == timestamp }) else { return }
        profile?.posts[idx].text = result.newText
        profile?.posts[idx].lang = result.lang
        profile?.posts[idx].tags = result.tags.map { $0.split(separator: " ").map(String.init) } ?? []
        profile?.posts[idx].mood = result.mood
        profile?.posts[idx].visibility = result.visibility == .mention ? "mention" : nil
        if let newTs = result.newTimestamp {
            profile?.posts[idx].timestamp = newTs
            if let newDate = PostWriter.parseTimestamp(newTs) {
                profile?.posts[idx].date = newDate
            }
        }
    }

    func load() async {
        guard !isLoading else { return }
        isLoading = true
        errorMessage = nil
        defer { isLoading = false }
        do {
            profile = try await fetcher.fetch(from: feedURL)
            startEnrichingFollows()
        } catch {
            errorMessage = error.localizedDescription
        }
    }

    /// Force reload. Use after the profile was mutated remotely (e.g. after EditProfile saves).
    /// Bypasses caches so the newly-uploaded headers are visible immediately.
    func reload() async {
        guard !isLoading else { return }
        isLoading = true
        errorMessage = nil
        defer { isLoading = false }
        do {
            profile = try await fetcher.fetch(from: feedURL, bypassCache: true)
            startEnrichingFollows()
        } catch {
            errorMessage = error.localizedDescription
        }
    }

    /// Fetches each followed feed's header in parallel (cap: 8 concurrent)
    /// and merges nick + avatar into `enrichedFollows`. Runs in the
    /// background; the UI updates incrementally as results arrive.
    private func startEnrichingFollows() {
        enrichTask?.cancel()
        guard let follows = profile?.follows else { return }
        let pending = follows.filter { enrichedFollows[$0.url] == nil }
        guard !pending.isEmpty else { return }
        enrichTask = Task { [weak self] in
            await self?.enrich(urls: pending.map(\.url))
        }
    }

    private func enrich(urls: [URL]) async {
        let maxConcurrent = 8
        await withTaskGroup(of: (URL, FollowDetails?).self) { group in
            var iterator = urls.makeIterator()
            for _ in 0..<maxConcurrent {
                guard let url = iterator.next() else { break }
                group.addTask { await Self.fetchDetails(for: url) }
            }
            while let (url, details) = await group.next() {
                if Task.isCancelled { group.cancelAll(); return }
                if let details { enrichedFollows[url] = details }
                if let next = iterator.next() {
                    group.addTask { await Self.fetchDetails(for: next) }
                }
            }
        }
    }

    private static func fetchDetails(for url: URL) async -> (URL, FollowDetails?) {
        guard let content = try? await FeedFetcher().fetch(from: url) else { return (url, nil) }
        let parsed = OrgSocialParser().parse(content)
        let details = FollowDetails(nick: parsed.nick, avatar: parsed.avatar)
        return (url, details)
    }
}