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

import SwiftUI
import SwiftData

// MARK: - Scroll progress tracking

private struct ContentFrameKey: PreferenceKey {
    static var defaultValue: CGRect = .zero
    static func reduce(value: inout CGRect, nextValue: () -> CGRect) { value = nextValue() }
}

// MARK: - ViewModel

@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 {
            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) }
    }
}

// MARK: - View

struct ArticleReaderView: View {
    let route: ArticleRoute

    @Environment(\.dismiss) private var dismiss
    @Environment(\.modelContext) private var modelContext
    @Environment(\.colorScheme) private var scheme
    @StateObject private var vm = ArticleReaderViewModel()
    @Query private var cachedArticles: [CachedArticle]
    @Query private var readStories:  [ReadStory]
    @Query private var savedStories: [SavedStory]
    @AppStorage("appearanceMode") private var appearanceMode: AppearanceMode = .dark
    @State private var showShare = false
    @State private var readProgress: Double = 0

    // Adaptive palette
    private var bg:       Color { scheme == .dark ? Color(hex: "0A0A0A") : Color(hex: "F8F7F4") }
    private var bodyFg:   Color { scheme == .dark ? Color(hex: "CECECE") : Color(hex: "1A1916") }
    private var headFg:   Color { scheme == .dark ? Color(hex: "F2F2F2") : Color(hex: "0F0E0C") }
    private var mutedFg:  Color { scheme == .dark ? Color(hex: "616161") : Color(hex: "888882") }
    private var hairline: Color { scheme == .dark ? Color(hex: "1F1F1F") : Color(hex: "E2E0D8") }
    private var skelFg:   Color { scheme == .dark ? Color(hex: "181818") : Color(hex: "E8E7E3") }

    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 > 28 ? String(h.prefix(28)).trimmingCharacters(in: .whitespaces) + "…" : h
    }

    var body: some View {
        ZStack {
            bg.ignoresSafeArea()
            VStack(spacing: 0) {
                progressBar
                scrollContent
            }
        }
        .navigationBarBackButtonHidden(true)
        .toolbar {
            ToolbarItem(placement: .topBarLeading) { backButton }
            ToolbarItemGroup(placement: .topBarTrailing) { trailingButtons }
        }
        .toolbarBackground(bg, for: .navigationBar)
        .toolbarBackground(.visible, for: .navigationBar)
        .sheet(isPresented: $showShare) { ShareSheet(items: shareContent) }
        .task { await vm.load(route: route, context: modelContext) }
    }

    // MARK: - Progress bar

    private var progressBar: some View {
        ZStack(alignment: .leading) {
            Rectangle().fill(hairline).frame(height: 2)
            Rectangle()
                .fill(Palette.orange)
                .frame(width: UIScreen.main.bounds.width * readProgress, height: 2)
                .animation(.linear(duration: 0.08), value: readProgress)
        }
    }

    // MARK: - Scroll content

    private var scrollContent: some View {
        ScrollView {
            VStack(spacing: 0) {
                if let article = vm.article {
                    articleBody(article)
                } else if vm.isLoading {
                    skeletonBody
                } else {
                    errorBody
                }
            }
            .padding(.bottom, 56)
            .background(
                GeometryReader { geo in
                    Color.clear.preference(
                        key: ContentFrameKey.self,
                        value: geo.frame(in: .named("reader"))
                    )
                }
            )
        }
        .coordinateSpace(name: "reader")
        .onPreferenceChange(ContentFrameKey.self) { frame in
            let viewH = UIScreen.main.bounds.height
            let scrollable = frame.height - viewH
            guard scrollable > 0 else { readProgress = 0; return }
            readProgress = Double(min(1, max(0, -frame.minY / scrollable)))
        }
    }

    // MARK: - Article layout

    @ViewBuilder
    private func articleBody(_ article: Article) -> some View {
        VStack(alignment: .leading, spacing: 0) {

            // Source + meta
            HStack(spacing: 10) {
                Text(article.source)
                    .font(.system(size: 11, weight: .bold))
                    .foregroundStyle(Palette.primaryText)
                    .lineLimit(1)
                    .padding(.horizontal, 10).padding(.vertical, 5)
                    .background(Palette.orange)
                    .clipShape(Capsule())

                Text(article.publishedAt.clockShort)
                    .font(.system(size: 12, weight: .regular, design: .monospaced))
                    .foregroundStyle(mutedFg)

                if isCached { cachedBadge }
                Spacer()
            }
            .padding(.horizontal, 22)
            .padding(.top, 24)
            .padding(.bottom, 20)

            // Headline
            Text(article.headline)
                .font(.system(size: 30, weight: .heavy))
                .foregroundStyle(headFg)
                .lineSpacing(2)
                .fixedSize(horizontal: false, vertical: true)
                .padding(.horizontal, 22)

            // Hero image
            heroImage(article.imageUrl)
                .padding(.horizontal, 16)
                .padding(.top, 22)

            // Author
            if let author = article.author, !author.isEmpty {
                Text(author.hasPrefix("By ") ? author : "By \(author)")
                    .font(.system(size: 12, weight: .medium, design: .monospaced))
                    .foregroundStyle(mutedFg)
                    .padding(.horizontal, 22)
                    .padding(.top, 18)
            }

            // Section break
            Rectangle()
                .fill(hairline)
                .frame(height: 1)
                .padding(.horizontal, 22)
                .padding(.top, 26)
                .padding(.bottom, 26)

            // Body — 17pt, generous line-height, readable contrast
            Text(article.body)
                .font(.system(size: 17, weight: .regular))
                .foregroundStyle(bodyFg)
                .lineSpacing(8.5)
                .fixedSize(horizontal: false, vertical: true)
                .frame(maxWidth: 680, alignment: .leading)
                .padding(.horizontal, 22)

            // Cluster
            if !vm.siblings.isEmpty {
                Rectangle()
                    .fill(hairline)
                    .frame(height: 1)
                    .padding(.horizontal, 22)
                    .padding(.top, 44)
                    .padding(.bottom, 24)
                clusterSection
                    .padding(.horizontal, 22)
            }
        }
    }

    // MARK: - Hero image

    @ViewBuilder
    private func heroImage(_ urlString: String?) -> some View {
        if let urlString, let url = URL(string: urlString) {
            AsyncImage(url: url) { phase in
                switch phase {
                case .success(let img):
                    img.resizable()
                        .aspectRatio(contentMode: .fill)
                        .transition(.opacity.animation(.easeIn(duration: 0.3)))
                case .empty:
                    PulsingSkeleton(color: skelFg)
                case .failure:
                    RoundedRectangle(cornerRadius: 12)
                        .fill(skelFg)
                        .overlay(
                            Image(systemName: "photo")
                                .font(.system(size: 24))
                                .foregroundStyle(mutedFg.opacity(0.5))
                        )
                @unknown default: EmptyView()
                }
            }
            .frame(height: 220)
            .frame(maxWidth: .infinity)
            .clipShape(RoundedRectangle(cornerRadius: 12))
        }
    }

    // MARK: - Cached badge

    private var cachedBadge: some View {
        HStack(spacing: 4) {
            Circle().fill(Color(hex: "4A9E4A")).frame(width: 5, height: 5)
            Text("Cached")
                .font(.system(size: 11, weight: .medium))
                .foregroundStyle(Color(hex: "4A9E4A"))
        }
    }

    // MARK: - Skeleton

    private var skeletonBody: some View {
        VStack(alignment: .leading, spacing: 0) {
            PulsingSkeleton(color: skelFg)
                .frame(width: 130, height: 26).clipShape(Capsule())
                .padding(.horizontal, 22).padding(.top, 24)

            VStack(alignment: .leading, spacing: 10) {
                PulsingSkeleton(color: skelFg).frame(height: 30)
                    .clipShape(RoundedRectangle(cornerRadius: 6))
                PulsingSkeleton(color: skelFg).frame(width: 260, height: 30)
                    .clipShape(RoundedRectangle(cornerRadius: 6))
            }
            .padding(.horizontal, 22).padding(.top, 16)

            PulsingSkeleton(color: skelFg)
                .frame(height: 220).clipShape(RoundedRectangle(cornerRadius: 12))
                .padding(.horizontal, 16).padding(.top, 22)

            VStack(alignment: .leading, spacing: 10) {
                ForEach(0..<5, id: \.self) { i in
                    PulsingSkeleton(color: skelFg)
                        .frame(width: i == 4 ? 180 : .infinity, height: 14)
                        .clipShape(RoundedRectangle(cornerRadius: 4))
                }
            }
            .padding(.horizontal, 22).padding(.top, 32)
        }
    }

    // MARK: - Error

    private var errorBody: some View {
        VStack(spacing: 12) {
            Image(systemName: "exclamationmark.triangle")
                .font(.system(size: 30))
                .foregroundStyle(mutedFg)
            Text(vm.error ?? "Article unavailable.")
                .font(.system(size: 14))
                .foregroundStyle(mutedFg)
                .multilineTextAlignment(.center)
        }
        .frame(maxWidth: .infinity)
        .padding(.top, 80)
        .padding(.horizontal, 40)
    }

    // MARK: - Cluster section

    private var clusterSection: some View {
        VStack(alignment: .leading, spacing: 0) {
            Text("MORE FROM THIS STORY")
                .font(.system(size: 10, weight: .bold, design: .monospaced))
                .kerning(0.7)
                .foregroundStyle(mutedFg)
                .padding(.bottom, 16)

            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: 6) {
            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(mutedFg)
            }
            Text(entry.headline)
                .font(.system(size: 15, weight: .regular))
                .foregroundStyle(bodyFg)
                .fixedSize(horizontal: false, vertical: true)
                .multilineTextAlignment(.leading)
        }
        .padding(.vertical, 14)
        .overlay(alignment: .bottom) {
            Rectangle().fill(hairline).frame(height: 0.5)
        }
        .contentShape(Rectangle())
    }

    // MARK: - Toolbar

    private var backButton: some View {
        Button { dismiss() } label: {
            HStack(spacing: 4) {
                Image(systemName: "chevron.left").font(.system(size: 14, weight: .semibold))
                Text(backTitle).font(.system(size: 15, weight: .regular)).lineLimit(1)
            }
            .foregroundStyle(Palette.orange)
        }
    }

    @ViewBuilder
    private var trailingButtons: some View {
        Button { showShare = true } label: {
            Image(systemName: "square.and.arrow.up")
                .font(.system(size: 15, weight: .medium))
                .foregroundStyle(mutedFg)
        }
        Button { toggleSave() } label: {
            Image(systemName: isSaved ? "bookmark.fill" : "bookmark")
                .font(.system(size: 15, weight: .medium))
                .foregroundStyle(isSaved ? Palette.orange : mutedFg)
        }
        Button { toggleRead() } label: {
            Image(systemName: isRead ? "checkmark.circle.fill" : "checkmark.circle")
                .font(.system(size: 16, weight: .medium))
                .foregroundStyle(isRead ? Palette.orange : mutedFg)
        }
        Menu {
            Picker("Appearance", selection: $appearanceMode) {
                ForEach(AppearanceMode.allCases, id: \.self) { mode in
                    Label(mode.label, systemImage: mode.icon).tag(mode)
                }
            }
            .pickerStyle(.inline)
        } label: {
            Image(systemName: appearanceMode.icon)
                .font(.system(size: 15, weight: .medium))
                .foregroundStyle(mutedFg)
        }
    }

    // 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
    }
}

// MARK: - Pulsing skeleton primitive

private struct PulsingSkeleton: View {
    let color: Color
    @State private var on = false

    var body: some View {
        color.opacity(on ? 0.9 : 0.45)
            .onAppear {
                withAnimation(.easeInOut(duration: 0.85).repeatForever()) { on = true }
            }
    }
}

// MARK: - Offline Article reconstruction

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
        )
    }
}