import Combine
import Foundation
import Martin
import SwiftUI

struct ConversationScreen: View {
    @Environment(\.router) var router
    @StateObject var messagesStore: MessagesStore
    @StateObject var attachments: AttachmentsStore

    @State private var autoScroll = true
    @State private var firstIsVisible = true

    var body: some View {
        ZStack {
            // Background color
            Color.Material.Background.light
                .ignoresSafeArea()

            // Content
            VStack(spacing: 0) {
                // Header
                SharedNavigationBar(
                    leftButton: .init(
                        image: Image(systemName: "chevron.left"),
                        action: {
                            router.dismissScreen()
                        }
                    ),
                    centerText: .init(text: centerText(), action: {
                        router.showScreen(.fullScreenCover) { _ in
                            ConversationSettingsScreen()
                        }
                    })
                )

                // Msg list
                let messages = messagesStore.messages
                if !messages.isEmpty {
                    ScrollViewReader { proxy in
                        ScrollView {
                            LazyVStack(spacing: 0) {
                                ForEach(messages) { message in
                                    ConversationMessageRow(message: message)
                                        .id(message.id)
                                        .flip()
                                        .onAppear {
                                            if message.id == messages.first?.id {
                                                firstIsVisible = true
                                                autoScroll = true
                                            }
                                            messagesStore.scrolledMessage(message.id)
                                        }
                                        .onDisappear {
                                            if message.id == messages.first?.id {
                                                firstIsVisible = false
                                                autoScroll = false
                                            }
                                        }
                                }
                            }
                        }
                        .flip()
                        .scrollDismissesKeyboard(.immediately)
                        .onChange(of: autoScroll) { new in
                            if new, !firstIsVisible {
                                withAnimation {
                                    proxy.scrollTo(messages.first?.id, anchor: .top)
                                }
                            }
                        }
                    }
                } else {
                    Spacer()
                }
            }
            .onTapGesture {
                UIApplication.shared.sendAction(#selector(UIResponder.resignFirstResponder), to: nil, from: nil, for: nil)
            }

            // Jump to last button
            if !autoScroll {
                VStack {
                    Spacer()
                    HStack {
                        Spacer()
                        Button {
                            autoScroll = true
                        } label: {
                            ZStack {
                                Circle()
                                    .fill(Color.Material.Shape.white)
                                Image(systemName: "arrow.down")
                                    .foregroundColor(.Material.Elements.active)
                            }
                            .frame(width: 40, height: 40)
                            .shadow(color: .black.opacity(0.2), radius: 4)
                            .padding(.trailing, 8)
                            .padding(.bottom, 8)
                        }
                    }
                }
            }
        }
        .environmentObject(messagesStore)
        .environmentObject(attachments)
        .safeAreaInset(edge: .bottom, spacing: 0) {
            ConversationTextInput(autoScroll: $autoScroll)
                .environmentObject(messagesStore)
                .environmentObject(attachments)
        }
    }

    private func centerText() -> String {
        let name = messagesStore.roster.name ?? JID(messagesStore.roster.contactBareJid).localPart
        if let name = name {
            return name
        } else {
            return L10n.Conversation.title
        }
    }
}