// ArticleReaderView.swift
// Jarvis — full article. Caches to SwiftData on load; reads from cache offline.

import SwiftUI
import SwiftData

@MainActor
final class ArticleReaderViewModel: ObservableObject {
    @Published var article: Article?
    @Published var siblings: [TimelineEntry] = []
    @Published var isLoading = false
    @Published var error: String?

    private let api = APIClient.shared

    func load(route: ArticleRoute, context: ModelContext) async {
        isLoading = true
        error = nil
        do {
            let art = try await api.fetchArticle(id: route.articleId)
            article = art
            cache(art, context: context)

            if let detail = try? await api.fetchStory(id: route.storyId) {
                siblings = detail.timeline
                    .filter { $0.articleId != route.articleId }
                    .sorted { $0.publishedAt < $1.publishedAt }
            }
        } catch {
            // Offline: fall back to the SwiftData cache.
            loadCached(route: route, context: context)
            if article == nil {
                self.error = (error as? APIError)?.errorDescription ?? error.localizedDescription
            }
        }
        isLoading = false
    }

    private func cache(_ art: Article, context: ModelContext) {
        let id = art.id
        let existing = try? context.fetch(
            FetchDescriptor<CachedArticle>(predicate: #Predicate { $0.id == id })
        )
        if existing?.first == nil {
            context.insert(CachedArticle(from: art))
            try? context.save()
        }
    }

    private func loadCached(route: ArticleRoute, context: ModelContext) {
        let id = route.articleId
        if let cached = (try? context.fetch(
            FetchDescriptor<CachedArticle>(predicate: #Predicate { $0.id == id })
        ))?.first {
            article = Article(cached: cached)
        }
        let sid = route.storyId
        let arts = (try? context.fetch(
            FetchDescriptor<CachedArticle>(predicate: #Predicate { $0.storyId == sid })
        )) ?? []
        siblings = arts
            .filter { $0.id != route.articleId }
            .map { TimelineEntry(articleId: $0.id, source: $0.source, headline: $0.headline,
                                 publishedAt: $0.publishedAt, isBreaking: false) }
    }
}

struct ArticleReaderView: View {
    let route: ArticleRoute

    @Environment(\.dismiss) private var dismiss
    @Environment(\.modelContext) private var modelContext
    @StateObject private var vm = ArticleReaderViewModel()
    @Query private var cachedArticles: [CachedArticle]
    @Query private var readStories:  [ReadStory]
    @Query private var savedStories: [SavedStory]
    @State private var showShare = false

    private var article: Article? { vm.article }
    private var isCached: Bool { cachedArticles.contains { $0.id == route.articleId } }
    private var isRead:  Bool { readStories.contains  { $0.id == route.storyId } }
    private var isSaved: Bool { savedStories.contains { $0.id == route.storyId } }

    private var backTitle: String {
        let h = route.parentHeadline
        return h.count > 30 ? String(h.prefix(30)).trimmingCharacters(in: .whitespaces) + "…" : h
    }

    var body: some View {
        ZStack {
            Color.black.ignoresSafeArea()
            ScrollView {
                if let article {
                    content(article)
                } else if vm.isLoading {
                    ProgressView().tint(Palette.orange).padding(.top, 80)
                } else {
                    Text(vm.error ?? "Article unavailable.")
                        .font(.system(size: 14))
                        .foregroundStyle(Color(hex: "555555"))
                        .padding(.top, 80)
                }
            }
        }
        .navigationBarBackButtonHidden(true)
        .toolbar {
            ToolbarItem(placement: .topBarLeading) { backButton }
            ToolbarItemGroup(placement: .topBarTrailing) {
                Button { showShare = true } label: {
                    Image(systemName: "square.and.arrow.up")
                        .font(.system(size: 16, weight: .semibold))
                        .foregroundStyle(Color(hex: "888888"))
                }
                Button { toggleSave() } label: {
                    Image(systemName: isSaved ? "bookmark.fill" : "bookmark")
                        .font(.system(size: 16, weight: .semibold))
                        .foregroundStyle(isSaved ? Palette.orange : Color(hex: "888888"))
                }
                Button { toggleRead() } label: {
                    Image(systemName: isRead ? "checkmark.circle.fill" : "checkmark.circle")
                        .font(.system(size: 17, weight: .semibold))
                        .foregroundStyle(isRead ? Palette.orange : Color(hex: "888888"))
                }
            }
        }
        .toolbarBackground(Color.black, for: .navigationBar)
        .toolbarBackground(.visible, for: .navigationBar)
        .preferredColorScheme(.dark)
        .sheet(isPresented: $showShare) { ShareSheet(items: shareContent) }
        .task { await vm.load(route: route, context: modelContext) }
    }

    // MARK: - Actions

    private func toggleRead() {
        let id = route.storyId
        if let row = (try? modelContext.fetch(
                FetchDescriptor<ReadStory>(predicate: #Predicate { $0.id == id })))?.first {
            modelContext.delete(row)
        } else {
            modelContext.insert(ReadStory(id: id))
        }
        try? modelContext.save()
    }

    private func toggleSave() {
        let id = route.storyId
        if let row = (try? modelContext.fetch(
                FetchDescriptor<SavedStory>(predicate: #Predicate { $0.id == id })))?.first {
            modelContext.delete(row)
        } else {
            modelContext.insert(SavedStory(id: id))
        }
        try? modelContext.save()
    }

    private var shareContent: [Any] {
        guard let art = vm.article else { return [] }
        var items: [Any] = ["\(art.headline)\n\nvia Jarvis"]
        if !art.sourceUrl.isEmpty, let url = URL(string: art.sourceUrl) {
            items.append(url)
        }
        return items
    }

    private var backButton: some View {
        Button { dismiss() } label: {
            HStack(spacing: 4) {
                Image(systemName: "chevron.left").font(.system(size: 15, weight: .bold))
                Text(backTitle).font(.system(size: 16, weight: .regular)).lineLimit(1)
            }
            .foregroundStyle(Palette.orange)
        }
    }

    @ViewBuilder
    private func content(_ article: Article) -> some View {
        VStack(alignment: .leading, spacing: 16) {
            // Source pill + timestamp + cached badge
            HStack(spacing: 10) {
                Text(article.source)
                    .font(.system(size: 12, weight: .bold))
                    .foregroundStyle(.white)
                    .padding(.horizontal, 10).padding(.vertical, 5)
                    .background(Palette.orange)
                    .clipShape(Capsule())
                Text(article.publishedAt.clockShort)
                    .font(.system(size: 12, weight: .regular, design: .monospaced))
                    .foregroundStyle(Color(hex: "666666"))
                if isCached { CachedBadge(text: "Cached") }
                Spacer()
            }

            Text(article.headline)
                .font(.system(size: 26, weight: .heavy))
                .foregroundStyle(.white)
                .fixedSize(horizontal: false, vertical: true)

            heroImage(article.imageUrl)

            if let author = article.author, !author.isEmpty {
                Text("By \(author)")
                    .font(.system(size: 13, weight: .bold))
                    .foregroundStyle(Color(hex: "777777"))
            }

            Text(article.body)
                .font(.system(size: 16, weight: .regular))
                .foregroundStyle(Palette.bodyText)       // #4A4A4A
                .lineSpacing(10)                          // ~1.65 line-height at 16pt
                .fixedSize(horizontal: false, vertical: true)

            if !vm.siblings.isEmpty {
                Divider().overlay(Palette.hairline).padding(.vertical, 8)
                clusterSection
            }
        }
        .padding(.horizontal, 18)
        .padding(.vertical, 12)
    }

    private func heroImage(_ urlString: String?) -> some View {
        let fallback = RoundedRectangle(cornerRadius: 10).fill(Palette.surface2)
        return Group {
            if let urlString, let url = URL(string: urlString) {
                AsyncImage(url: url) { phase in
                    switch phase {
                    case .success(let image):
                        image.resizable().aspectRatio(contentMode: .fill)
                    case .empty:
                        fallback.overlay(ProgressView().tint(Color(hex: "555555")))
                    case .failure:
                        fallback.overlay(Image(systemName: "photo")
                            .font(.system(size: 26)).foregroundStyle(Color(hex: "3A3A3A")))
                    @unknown default:
                        fallback
                    }
                }
            } else {
                fallback.overlay(Image(systemName: "photo")
                    .font(.system(size: 26)).foregroundStyle(Color(hex: "3A3A3A")))
            }
        }
        .frame(height: 200)
        .frame(maxWidth: .infinity)
        .clipShape(RoundedRectangle(cornerRadius: 10))
    }

    private var clusterSection: some View {
        VStack(alignment: .leading, spacing: 0) {
            Text("MORE FROM THIS CLUSTER")
                .font(.system(size: 10, weight: .bold, design: .monospaced))
                .kerning(0.8)
                .foregroundStyle(Color(hex: "555555"))
                .padding(.bottom, 12)

            ForEach(vm.siblings.prefix(3)) { entry in
                NavigationLink(value: ArticleRoute(articleId: entry.articleId,
                                                   storyId: route.storyId,
                                                   parentHeadline: route.parentHeadline)) {
                    clusterRow(entry)
                }
                .buttonStyle(.plain)
            }
        }
    }

    private func clusterRow(_ entry: TimelineEntry) -> some View {
        VStack(alignment: .leading, spacing: 5) {
            HStack {
                Text(entry.source)
                    .font(.system(size: 12, weight: .bold))
                    .foregroundStyle(Palette.orange)
                Spacer()
                Text(entry.publishedAt.clockShort)
                    .font(.system(size: 11, weight: .regular, design: .monospaced))
                    .foregroundStyle(Color(hex: "555555"))
            }
            Text(entry.headline)
                .font(.system(size: 15, weight: .regular))
                .foregroundStyle(Color(hex: "CFCFCF"))
                .fixedSize(horizontal: false, vertical: true)
                .multilineTextAlignment(.leading)
        }
        .padding(.vertical, 12)
        .overlay(alignment: .bottom) { Rectangle().fill(Palette.hairline).frame(height: 0.5) }
        .contentShape(Rectangle())
    }
}

// Reconstruct an Article from its cached copy for offline display.
extension Article {
    init(cached: CachedArticle) {
        self.init(
            id: cached.id,
            storyId: cached.storyId,
            source: cached.source,
            sourceUrl: "",
            headline: cached.headline,
            body: cached.body,
            imageUrl: cached.imageUrl,
            author: cached.author,
            publishedAt: cached.publishedAt
        )
    }
}