import SwiftUI

// 消息（按设备聚合，社交软件式）：会话列表（每个对端设备一行）→ 点进 ConversationView 聊天线程。
// 会话由引擎 conversations() 合成——有消息历史的设备 ∪ 当前可达设备（在线 / 可唤醒，供发起新会话）。
// 可达设备可发（在线即时达、离线 iOS 走 APNs 唤醒）；不可达的离线设备（离线桌面 / 浏览器）仅可查看
// 历史、撰写栏禁用。删除：单条消息（线程内长按）+ 整段会话（列表滑动 / 长按）——避免废会话堆积。
struct MessagesView: View
{
    @Environment(EngineController.self) private var engine
    @State private var showClearConfirm = false

    var body: some View
    {
        Group
        {
            let convos = engine.conversations()
            if convos.isEmpty
            {
                ContentUnavailableView(t("ios.messages.empty"), systemImage: "message")
            }
            else
            {
                List
                {
                    ForEach(convos)
                    { convo in
                        NavigationLink(value: convo.peerName)
                        {
                            conversationRow(convo)
                        }
                        // 长条行统一：滑动 + 长按都能删整段会话（清掉该设备全部消息记录）。
                        .swipeActions(edge: .trailing)
                        {
                            Button(role: .destructive) { engine.deleteConversation(convo.peerName) }
                            label: { Label(t("ios.messages.deleteConversation"), systemImage: "trash") }
                        }
                        .contextMenu
                        {
                            Button(role: .destructive) { engine.deleteConversation(convo.peerName) }
                            label: { Label(t("ios.messages.deleteConversation"), systemImage: "trash") }
                        }
                    }
                }
                .listStyle(.plain)
            }
        }
        .navigationTitle(t("ios.tab.messages"))
        .navigationDestination(for: String.self) { peer in ConversationView(peerName: peer) }
        .toolbar
        {
            if !engine.messages.isEmpty
            {
                ToolbarItem(placement: .topBarTrailing)
                {
                    Button(role: .destructive) { showClearConfirm = true }
                    label: { Label(t("ios.records.clear"), systemImage: "trash") }
                }
            }
        }
        .confirmationDialog(t("ios.records.clearConfirm"), isPresented: $showClearConfirm, titleVisibility: .visible)
        {
            Button(t("ios.records.clear"), role: .destructive) { engine.clearMessages() }
            Button(t("common.cancel"), role: .cancel) { }
        }
    }

    private func conversationRow(_ convo: ConversationItem) -> some View
    {
        HStack(spacing: 12)
        {
            Image(systemName: deviceSymbol(convo.deviceType))
                .font(.oTitle3)
                .foregroundStyle(convo.online ? Color.green : Color.secondary)
                .frame(width: 28)
            VStack(alignment: .leading, spacing: 3)
            {
                Text(convo.peerName)
                    .font(.oBody)
                    .lineLimit(1)
                Text(previewText(convo))
                    .font(.oCaption)
                    .foregroundStyle(.secondary)
                    .lineLimit(1)
            }
            Spacer()
            VStack(alignment: .trailing, spacing: 5)
            {
                if convo.lastAt > 0
                {
                    Text(relativeTime(convo.lastAt))
                        .font(.oCaption2)
                        .foregroundStyle(.secondary)
                }
                // 该设备未读红点（社交软件式逐设备计数）；消息 tab 徽标＝各设备未读总和（engine.unreadMessages）。
                let unread = engine.unread(for: convo.peerName)
                if unread > 0
                {
                    Text("\(unread)")
                        .font(.oCaption2)
                        .fontWeight(.bold)
                        .foregroundStyle(.white)
                        .padding(.horizontal, 7)
                        .padding(.vertical, 2)
                        .background(Color.cdropAccent, in: Capsule())
                }
            }
        }
        .padding(.vertical, 4)
    }

    // 会话副行预览：有历史显示最近一条（本端发出的加「你：」前缀）；无历史（仅可达）显示发起提示。
    private func previewText(_ convo: ConversationItem) -> String
    {
        if convo.lastText.isEmpty
        {
            return convo.reachable ? t("ios.messages.startHint") : t("ios.messages.viewOnly")
        }
        return convo.lastOutgoing ? "\(t("ios.messages.youPrefix"))\(convo.lastText)" : convo.lastText
    }
}

// 单个设备的聊天线程：自上而下旧→新 + 底部撰写栏。可达设备（在线 / 可唤醒）才显示撰写栏；
// 不可达离线设备仅查看历史、底部显示「仅查看」提示。长按消息可删单条。
struct ConversationView: View
{
    @Environment(EngineController.self) private var engine
    let peerName: String
    @State private var draft = ""

    private var thread: [MessageItem] { engine.thread(with: peerName) }
    private var reachable: Bool { engine.canMessage(peerName) }

    var body: some View
    {
        VStack(spacing: 0)
        {
            if thread.isEmpty
            {
                ContentUnavailableView(t("ios.messages.empty"), systemImage: "message")
                    .frame(maxWidth: .infinity, maxHeight: .infinity)
            }
            else
            {
                ScrollViewReader
                { proxy in
                    ScrollView
                    {
                        LazyVStack(alignment: .leading, spacing: 10)
                        {
                            ForEach(thread)
                            { msg in
                                messageRow(msg)
                                    .id(msg.id)
                                    .contextMenu
                                    {
                                        Button(role: .destructive) { engine.deleteMessage(msg.id) }
                                        label: { Label(t("transfer.action.delete"), systemImage: "trash") }
                                    }
                            }
                        }
                        .padding()
                    }
                    .onChange(of: thread.count) { scrollToLast(proxy) }
                    .onAppear { scrollToLast(proxy) }
                }
            }
            composeBar
        }
        .navigationTitle(peerName)
        .navigationBarTitleDisplayMode(.inline)
        // 进入会话：记为当前会话（其后到达的消息不计未读）+ 清该设备已积累未读；离开置空。
        .onAppear
        {
            engine.setActiveConversation(peerName)
            engine.markConversationRead(peerName)
        }
        .onDisappear { engine.setActiveConversation(nil) }
    }

    private func scrollToLast(_ proxy: ScrollViewProxy)
    {
        guard let last = thread.last else { return }
        withAnimation { proxy.scrollTo(last.id, anchor: .bottom) }
    }

    private func messageRow(_ msg: MessageItem) -> some View
    {
        let outgoing = msg.direction == "outgoing"
        return HStack
        {
            if outgoing { Spacer(minLength: 48) }
            Text(msg.text)
                .padding(.horizontal, 12)
                .padding(.vertical, 8)
                .background(outgoing ? Color.cdropAccent.opacity(0.18) : Color(.secondarySystemBackground),
                            in: RoundedRectangle(cornerRadius: 14))
                .textSelection(.enabled)
            if !outgoing { Spacer(minLength: 48) }
        }
        .frame(maxWidth: .infinity, alignment: outgoing ? .trailing : .leading)
    }

    @ViewBuilder
    private var composeBar: some View
    {
        if reachable
        {
            HStack(spacing: 10)
            {
                TextField(t("ios.messages.placeholder"), text: $draft, axis: .vertical)
                    .textFieldStyle(.roundedBorder)
                    .lineLimit(1 ... 4)
                    .submitLabel(.send)
                    .onSubmit { send() }
                Button { send() }
                label: { Image(systemName: "paperplane.fill").font(.oTitle3) }
                    .disabled(draft.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty)
            }
            .padding()
            .background(.bar)
        }
        else
        {
            Text(t("ios.messages.viewOnly"))
                .font(.oCaption)
                .foregroundStyle(.secondary)
                .frame(maxWidth: .infinity)
                .padding()
                .background(.bar)
        }
    }

    private func send()
    {
        let text = draft.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !text.isEmpty else { return }
        engine.sendMessage(to: peerName, text: text)
        draft = ""
    }
}