import SwiftUI

struct PrivateChatView: View {
    let chat: PrivateChatListItem
    let currentUserId: String?

    @StateObject private var viewModel: PrivateChatViewModel
    @State private var hasPositionedToBottom: Bool = false
    @State private var draftText: String = ""
    @State private var inputTab: ComposerTab = .chat
    @State private var isVideoPreferred: Bool = false
    @FocusState private var isComposerFocused: Bool
    @EnvironmentObject private var messageCenter: IncomingMessageCenter

    init(chat: PrivateChatListItem, currentUserId: String?) {
        self.chat = chat
        self.currentUserId = currentUserId
        _viewModel = StateObject(wrappedValue: PrivateChatViewModel(chatId: chat.chatId, currentUserId: currentUserId))
    }

    var body: some View {
        ScrollViewReader { proxy in
            content
                .onChange(of: viewModel.messages.count) { _ in
                    guard !viewModel.isLoadingMore,
                          let lastId = viewModel.messages.last?.id else { return }
                    DispatchQueue.main.async {
                        withAnimation(.easeInOut(duration: 0.2)) {
                            proxy.scrollTo(lastId, anchor: .bottom)
                        }
                        hasPositionedToBottom = true
                    }
                }
        }
        .navigationTitle(title)
        .navigationBarTitleDisplayMode(.inline)
        .task {
            viewModel.loadInitialHistory()
        }
        .onAppear {
            messageCenter.activeChatId = chat.chatId
        }
        .onChange(of: viewModel.isInitialLoading) { isLoading in
            if isLoading {
                hasPositionedToBottom = false
            }
        }
        .safeAreaInset(edge: .bottom) {
            composer
        }
        .onDisappear {
            if messageCenter.activeChatId == chat.chatId {
                messageCenter.activeChatId = nil
            }
        }
    }

    @ViewBuilder
    private var content: some View {
        if viewModel.isInitialLoading && viewModel.messages.isEmpty {
            ProgressView(NSLocalizedString("Загрузка сообщений…", comment: ""))
                .frame(maxWidth: .infinity, maxHeight: .infinity)
        } else if let error = viewModel.errorMessage, viewModel.messages.isEmpty {
            errorView(message: error)
        } else {
            ScrollView {
                LazyVStack(alignment: .leading, spacing: 12) {
                    if viewModel.isLoadingMore {
                        loadingMoreView
                    } else if viewModel.messages.isEmpty {
                        emptyState
                    }

                    ForEach(viewModel.messages) { message in
                        messageRow(for: message)
                            .id(message.id)
                            .onAppear {
                                guard hasPositionedToBottom else { return }
                                viewModel.loadMoreIfNeeded(for: message)
                            }
                    }

                    if let message = viewModel.errorMessage,
                       !message.isEmpty,
                       !viewModel.messages.isEmpty {
                        errorBanner(message: message)
                    }
                }
                .padding(.vertical, 12)
            }
            .refreshable {
                viewModel.refresh()
            }
        }
    }

    private var emptyState: some View {
        Text(NSLocalizedString("В чате пока нет сообщений.", comment: ""))
            .font(.footnote)
            .foregroundColor(.secondary)
            .frame(maxWidth: .infinity, alignment: .center)
            .padding(.top, 32)
    }

    private var loadingMoreView: some View {
        HStack {
            ProgressView()
            Text(NSLocalizedString("Загружаем ранние сообщения…", comment: ""))
                .font(.caption)
        }
        .frame(maxWidth: .infinity)
        .padding(.vertical, 8)
    }

    private func errorView(message: String) -> some View {
        VStack(spacing: 12) {
            Text(message)
                .font(.body)
                .multilineTextAlignment(.center)
                .foregroundColor(.primary)

            Button(action: { viewModel.refresh() }) {
                Text(NSLocalizedString("Повторить", comment: ""))
                    .font(.body)
            }
        }
        .padding()
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }

    private func messageRow(for message: MessageItem) -> some View {
        let isCurrentUser = currentUserId.map { $0 == message.senderId } ?? false
        return HStack(alignment: .bottom, spacing: 12) {
            if isCurrentUser { Spacer(minLength: 32) }

            VStack(alignment: isCurrentUser ? .trailing : .leading, spacing: 6) {
//                if !isCurrentUser {
//                    Text(senderName(for: message))
//                        .font(.caption)
//                        .foregroundColor(.secondary)
//                }

                Text(contentText(for: message))
                    .font(.body)
                    .foregroundColor(isCurrentUser ? .white : .primary)
                    .multilineTextAlignment(isCurrentUser ? .trailing : .leading)

                Text(timestamp(for: message))
                    .font(.caption2)
                    .foregroundColor(isCurrentUser ? Color.white.opacity(0.8) : .secondary)
            }
            .padding(.vertical, 10)
            .padding(.horizontal, 12)
            .background(isCurrentUser ? Color.accentColor : Color(.secondarySystemBackground))
            .clipShape(RoundedRectangle(cornerRadius: 16, style: .continuous))
            .frame(maxWidth: messageBubbleMaxWidth, alignment: isCurrentUser ? .trailing : .leading)
            .fixedSize(horizontal: false, vertical: true)

            if !isCurrentUser { Spacer(minLength: 32) }
        }
        .padding(.horizontal, 16)
    }

    private var messageBubbleMaxWidth: CGFloat {
        min(UIScreen.main.bounds.width * 0.72, 360)
    }

    private func senderName(for message: MessageItem) -> String {
        if let full = message.senderData?.fullName, !full.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {
            return full
        }
        if let custom = message.senderData?.customName, !custom.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {
            return custom
        }
        if let login = message.senderData?.login, !login.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {
            return "@\(login)"
        }
        return message.senderId
    }

    private func timestamp(for message: MessageItem) -> String {
        guard let date = message.createdAt else {
            return ""
        }
        return Self.timeFormatter.string(from: date)
    }

    private func contentText(for message: MessageItem) -> String {
        guard let content = message.content?.trimmingCharacters(in: .whitespacesAndNewlines), !content.isEmpty else {
            return NSLocalizedString("(без текста)", comment: "")
        }
        return content
    }

    private func errorBanner(message: String) -> some View {
        HStack {
            Image(systemName: "exclamationmark.triangle.fill")
                .foregroundColor(.orange)
            Text(message)
                .font(.footnote)
                .foregroundColor(.primary)
        }
        .padding()
        .background(Color(.secondarySystemBackground))
        .clipShape(RoundedRectangle(cornerRadius: 12, style: .continuous))
        .padding(.horizontal, 16)
        .padding(.top, 8)
    }

    private var composer: some View {
        VStack(spacing: 10) {
            Divider()

            HStack(spacing: 12) {
                composerToolbarButton(systemName: "paperclip", label: NSLocalizedString("Вложения", comment: "")) {
                    // TODO: hook to attachments action
                }

                composerModeButton(.chat)
                composerModeButton(.stickers)

                Spacer(minLength: 0)
            }

            HStack(alignment: .bottom, spacing: 12) {
                HStack(alignment: .center, spacing: 8) {
                    Image(systemName: inputTab.iconName)
                        .foregroundColor(.secondary)
                    TextField(inputTab.placeholder, text: $draftText, axis: .vertical)
                        .lineLimit(1...4)
                        .focused($isComposerFocused)
                        .submitLabel(.send)
                        .disabled(viewModel.isSending || currentUserId == nil)
                        .onSubmit { sendCurrentMessage() }
                }
                .padding(.vertical, 10)
                .padding(.horizontal, 12)
                .background(Color(.secondarySystemBackground))
                .clipShape(RoundedRectangle(cornerRadius: 18, style: .continuous))

                if !isSendAvailable {
                    Button(action: { isVideoPreferred.toggle() }) {
                        Image(systemName: isVideoPreferred ? "video.fill" : "mic.fill")
                            .font(.system(size: 18, weight: .semibold))
                            .foregroundColor(.accentColor)
                            .frame(width: 40, height: 40)
                            .background(Color.accentColor.opacity(0.12))
                            .clipShape(Circle())
                    }
                    .buttonStyle(.plain)
                } else {
                    sendButton
                }
            }
        }
        .padding(.horizontal, 16)
        .padding(.top, 10)
        .padding(.bottom, 8)
        .background(.ultraThinMaterial)
    }

    private var isSendDisabled: Bool {
        draftText.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty || viewModel.isSending || currentUserId == nil
    }

    private var isSendAvailable: Bool {
        !draftText.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty && currentUserId != nil
    }

    private var sendButton: some View {
        Button(action: sendCurrentMessage) {
            Image(systemName: viewModel.isSending ? "hourglass" : "paperplane.fill")
                .font(.system(size: 18, weight: .semibold))
                .foregroundColor(.white)
                .frame(width: 40, height: 40)
                .background(Color.accentColor)
                .clipShape(Circle())
        }
        .disabled(isSendDisabled)
        .buttonStyle(.plain)
    }

    private func composerToolbarButton(systemName: String, label: String, action: @escaping () -> Void) -> some View {
        Button(action: action) {
            VStack(spacing: 4) {
                Image(systemName: systemName)
                    .font(.system(size: 16, weight: .medium))
                Text(label)
                    .font(.caption2)
            }
            .foregroundColor(.primary)
            .frame(width: 64, height: 44)
            .background(Color(.secondarySystemBackground))
            .clipShape(RoundedRectangle(cornerRadius: 12, style: .continuous))
        }
        .buttonStyle(.plain)
    }

    private func composerModeButton(_ tab: ComposerTab) -> some View {
        Button(action: { inputTab = tab }) {
            Text(tab.title)
                .font(.caption)
                .fontWeight(inputTab == tab ? .semibold : .regular)
                .padding(.vertical, 8)
                .padding(.horizontal, 14)
                .background(
                    Group {
                        if inputTab == tab {
                            Color.accentColor.opacity(0.15)
                        } else {
                            Color(.secondarySystemBackground)
                        }
                    }
                )
                .foregroundColor(inputTab == tab ? .accentColor : .primary)
                .clipShape(Capsule())
        }
        .buttonStyle(.plain)
    }

    private func sendCurrentMessage() {
        let text = draftText.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !text.isEmpty else { return }

        viewModel.sendMessage(text: text) { success in
            if success {
                draftText = ""
                hasPositionedToBottom = true
            }
        }
    }

    private enum ComposerTab: String {
        case chat
        case stickers

        var title: String {
            switch self {
            case .chat: return NSLocalizedString("Чат", comment: "")
            case .stickers: return NSLocalizedString("Стикеры", comment: "")
            }
        }

        var iconName: String {
            switch self {
            case .chat: return "text.bubble"
            case .stickers: return "face.smiling"
            }
        }

        var placeholder: String {
            switch self {
            case .chat: return NSLocalizedString("Сообщение", comment: "")
            case .stickers: return NSLocalizedString("Поиск стикеров", comment: "")
            }
        }
    }

    private static let timeFormatter: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateStyle = .none
        formatter.timeStyle = .short
        return formatter
    }()

    private var title: String {
        if let full = chat.chatData?.fullName, !full.isEmpty {
            return full
        }
        if let custom = chat.chatData?.customName, !custom.isEmpty {
            return custom
        }
        if let login = chat.chatData?.login, !login.isEmpty {
            return "@\(login)"
        }
        return NSLocalizedString("Чат", comment: "")
    }
}

// MARK: - Preview

// Previews intentionally omitted - MessageItem has custom decoding-only initializer.