//
//  ChatsTab.swift
//  VolnahubApp
//
//  Created by cheykrym on 09/06/2025.
//

import SwiftUI

struct ChatsTab: View {
    @StateObject private var viewModel = PrivateChatsViewModel()

    var body: some View {
        content
            .background(Color(UIColor.systemBackground))
            .onAppear {
                viewModel.loadInitialChats()
            }
    }

    @ViewBuilder
    private var content: some View {
        if viewModel.isInitialLoading && viewModel.chats.isEmpty {
            loadingState
        } else if let message = viewModel.errorMessage, viewModel.chats.isEmpty {
            errorState(message: message)
        } else if viewModel.chats.isEmpty {
            emptyState
        } else {
            chatList
        }
    }

    private var chatList: some View {
        List {
            if let message = viewModel.errorMessage {
                Section {
                    HStack(alignment: .top, spacing: 8) {
                        Image(systemName: "exclamationmark.triangle.fill")
                            .foregroundColor(.orange)
                        Text(message)
                            .font(.subheadline)
                            .foregroundColor(.orange)
                        Spacer(minLength: 0)
                        Button(action: { viewModel.refresh() }) {
                            Text(NSLocalizedString("Обновить", comment: ""))
                                .font(.subheadline)
                        }
                    }
                    .padding(.vertical, 4)
                }
                .listRowInsets(EdgeInsets(top: 8, leading: 16, bottom: 8, trailing: 16))
            }

            ForEach(viewModel.chats) { chat in
                ChatRowView(chat: chat)
                    .contentShape(Rectangle())
                    .onAppear {
                        viewModel.loadMoreIfNeeded(currentItem: chat)
                    }
            }

            if viewModel.isLoadingMore {
                loadingMoreRow
            }
        }
        .listStyle(.plain)
    }

    private var loadingState: some View {
        VStack(spacing: 12) {
            ProgressView()
            Text(NSLocalizedString("Загружаем чаты…", comment: ""))
                .font(.subheadline)
                .foregroundColor(.secondary)
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }

    private func errorState(message: String) -> some View {
        VStack(spacing: 12) {
            Image(systemName: "exclamationmark.bubble")
                .font(.system(size: 48))
                .foregroundColor(.orange)
            Text(message)
                .font(.body)
                .multilineTextAlignment(.center)
                .foregroundColor(.primary)
            Button(action: { viewModel.loadInitialChats(force: true) }) {
                Text(NSLocalizedString("Повторить", comment: ""))
                    .font(.headline)
            }
            .buttonStyle(.borderedProminent)
        }
        .padding()
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }

    private var emptyState: some View {
        VStack(spacing: 12) {
            Image(systemName: "bubble.left")
                .font(.system(size: 48))
                .foregroundColor(.secondary)
            Text(NSLocalizedString("Пока что у вас нет чатов", comment: ""))
                .font(.body)
                .foregroundColor(.secondary)
            Button(action: { viewModel.refresh() }) {
                Text(NSLocalizedString("Обновить", comment: ""))
            }
            .buttonStyle(.bordered)
        }
        .padding()
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }

    private var loadingMoreRow: some View {
        HStack {
            Spacer()
            ProgressView()
                .padding(.vertical, 12)
            Spacer()
        }
        .listRowSeparator(.hidden)
    }
}

private struct ChatRowView: View {
    let chat: PrivateChatListItem

    private var title: String {
        switch chat.chatType {
        case .self:
            return NSLocalizedString("Избранные сообщения", comment: "")
        case .privateChat, .unknown:
            if let custom = chat.chatData?.customName, !custom.isEmpty {
                return custom
            }
            if let full = chat.chatData?.fullName, !full.isEmpty {
                return full
            }
            if let login = chat.chatData?.login, !login.isEmpty {
                return "@\(login)"
            }
            return NSLocalizedString("Неизвестный пользователь", comment: "")
        }
    }

    private var subtitle: String {
        guard let message = chat.lastMessage else {
            return NSLocalizedString("Нет сообщений", comment: "")
        }

        if let content = message.content, !content.isEmpty {
            return content
        }

        if message.mediaLink != nil {
            return NSLocalizedString("Вложение", comment: "")
        }

        return NSLocalizedString("Сообщение", comment: "")
    }

    private var timestamp: String? {
        let date = chat.lastMessage?.createdAt ?? chat.createdAt
        guard let date else { return nil }
        return ChatRowView.timeFormatter.string(from: date)
    }

    private var initial: String {
        return String(title.prefix(1)).uppercased()
    }

    private var subtitleColor: Color {
        chat.unreadCount > 0 ? .primary : .secondary
    }

    var body: some View {
        HStack(spacing: 12) {
            Circle()
                .fill(Color.accentColor.opacity(0.15))
                .frame(width: 44, height: 44)
                .overlay(
                    Text(initial)
                        .font(.headline)
                        .foregroundColor(Color.accentColor)
                )

            VStack(alignment: .leading, spacing: 4) {
                Text(title)
                    .fontWeight(chat.unreadCount > 0 ? .semibold : .regular)
                    .foregroundColor(.primary)
                    .lineLimit(1)

                Text(subtitle)
                    .font(.subheadline)
                    .foregroundColor(subtitleColor)
                    .lineLimit(2)
            }

            Spacer()

            VStack(alignment: .trailing, spacing: 6) {
                if let timestamp {
                    Text(timestamp)
                        .font(.caption)
                        .foregroundColor(.secondary)
                }

                if chat.unreadCount > 0 {
                    Text("\(chat.unreadCount)")
                        .font(.caption2.bold())
                        .foregroundColor(.white)
                        .padding(.horizontal, 8)
                        .padding(.vertical, 4)
                        .background(
                            Capsule().fill(Color.accentColor)
                        )
                }
            }
        }
        .padding(.vertical, 8)
    }

    private static let timeFormatter: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateStyle = .short
        formatter.timeStyle = .short
        return formatter
    }()
}

struct ChatsTab_Previews: PreviewProvider {
    static var previews: some View {
        ChatsTab()
            .environmentObject(ThemeManager())
    }
}