import HostRegistry
import SwiftUI
import WireProtocol

/// T-iOS-13 · Session list screen (merged chooser + dashboard). Pure
/// presentation over `SessionListViewModel` — polling cadence, badge priority,
/// staleness, optimistic kill and the navigation signal are all VM logic,
/// unit-tested in `SessionListViewModelTests`.
///
/// The T-iOS-15 wiring provides `onOpen` (push `TerminalScreen`, open with
/// `request.sessionId` — nil = new session) and `onAddHost` (present the
/// pairing sheet; call `viewModel.reloadHosts()` when it completes).
struct SessionListScreen: View {
    var viewModel: SessionListViewModel
    /// Navigation hook: fired once per `OpenRequest` (unique id per tap).
    var onOpen: (SessionListViewModel.OpenRequest) -> Void = { _ in }
    /// Host-switch header hook: "添加主机" entry (pairing sheet, T-iOS-15).
    var onAddHost: () -> Void = {}

    var body: some View {
        content
            .navigationTitle(ScreenCopy.title)
            .toolbar { hostMenu }
            .onAppear { viewModel.appeared() }
            .onDisappear { viewModel.disappeared() }
            .onChange(of: viewModel.openRequest) { _, request in
                guard let request else { return }
                onOpen(request)
            }
    }

    @ViewBuilder private var content: some View {
        switch viewModel.emptyState {
        case .notPaired:
            notPairedView
        case .noSessions:
            noSessionsView
        case nil:
            sessionList
        }
    }

    // MARK: - List

    private var sessionList: some View {
        List {
            if let message = viewModel.fetchErrorMessage {
                errorRow(message)
            }
            if let message = viewModel.killErrorMessage {
                errorRow(message)
            }
            Button {
                viewModel.requestNewSession()
            } label: {
                Label(ScreenCopy.newSession, systemImage: "plus.circle.fill")
            }
            ForEach(viewModel.rows) { row in
                Button {
                    viewModel.openSession(id: row.id)
                } label: {
                    SessionRowView(row: row)
                }
                .swipeActions(edge: .trailing, allowsFullSwipe: true) {
                    Button(role: .destructive) {
                        Task { await viewModel.kill(sessionId: row.id) }
                    } label: {
                        Label(ScreenCopy.kill, systemImage: "xmark.circle.fill")
                    }
                }
            }
        }
        .refreshable { await viewModel.refresh() }
    }

    private func errorRow(_ message: String) -> some View {
        Label(message, systemImage: "exclamationmark.triangle")
            .font(.footnote)
            .foregroundStyle(.red)
    }

    // MARK: - Empty states

    private var notPairedView: some View {
        ContentUnavailableView {
            Label(ScreenCopy.notPairedTitle, systemImage: "personalhotspot")
        } description: {
            Text(ScreenCopy.notPairedHint)
        } actions: {
            Button(ScreenCopy.addHost) { onAddHost() }
                .buttonStyle(.borderedProminent)
        }
    }

    private var noSessionsView: some View {
        ContentUnavailableView {
            Label(ScreenCopy.noSessionsTitle, systemImage: "terminal")
        } description: {
            Text(ScreenCopy.noSessionsHint)
        } actions: {
            Button(ScreenCopy.newSession) { viewModel.requestNewSession() }
                .buttonStyle(.borderedProminent)
        }
    }

    // MARK: - Host-switch header (multi-host from HostStore)

    private var hostMenu: some ToolbarContent {
        ToolbarItem(placement: .topBarTrailing) {
            Menu {
                ForEach(viewModel.hosts) { host in
                    Button {
                        Task { await viewModel.selectHost(id: host.id) }
                    } label: {
                        if host.id == viewModel.activeHost?.id {
                            Label(host.name, systemImage: "checkmark")
                        } else {
                            Text(host.name)
                        }
                    }
                }
                Divider()
                Button {
                    onAddHost()
                } label: {
                    Label(ScreenCopy.addHost, systemImage: "plus")
                }
            } label: {
                Label(
                    viewModel.activeHost?.name ?? ScreenCopy.hostMenuFallback,
                    systemImage: "desktopcomputer"
                )
            }
        }
    }
}

// MARK: - Row

private struct SessionRowView: View {
    let row: SessionListViewModel.SessionRow

    var body: some View {
        HStack(alignment: .top, spacing: Metrics.rowSpacing) {
            indicator
                .frame(width: Metrics.indicatorWidth)
            VStack(alignment: .leading, spacing: Metrics.rowInnerSpacing) {
                Text(title)
                    .font(.body)
                    .lineLimit(1)
                Text(meta)
                    .font(.caption)
                    .foregroundStyle(.secondary)
                if let telemetry = row.telemetry, !telemetry.isEmpty {
                    TelemetryChips(model: telemetry)
                }
            }
        }
        .opacity(row.info.exited ? Metrics.exitedOpacity : 1)
        .accessibilityElement(children: .combine)
    }

    /// ⚠ badge outranks the status dot (VM decides via `indicator`).
    @ViewBuilder private var indicator: some View {
        switch row.indicator {
        case .pendingApproval:
            Image(systemName: "exclamationmark.triangle.fill")
                .foregroundStyle(.orange)
                .accessibilityLabel(ScreenCopy.pendingBadgeLabel)
        case .status(let status):
            Circle()
                .fill(Self.dotColor(status))
                .frame(width: Metrics.dotSize, height: Metrics.dotSize)
                .padding(.top, Metrics.dotTopPadding)
                .accessibilityLabel(Text(status.rawValue))
        }
    }

    /// `cwd` is server-supplied display text (untrusted → plain Text only).
    private var title: String {
        guard let cwd = row.info.cwd, !cwd.isEmpty else { return ScreenCopy.unknownDirectory }
        return URL(fileURLWithPath: cwd).lastPathComponent
    }

    private var meta: String {
        var parts = [
            ScreenCopy.clientCount(row.info.clientCount),
            "\(row.info.cols)×\(row.info.rows)",
        ]
        if row.info.exited {
            parts.append(ScreenCopy.exitedTag)
        }
        return parts.joined(separator: " · ")
    }

    private static func dotColor(_ status: ClaudeStatus) -> Color {
        switch status {
        case .working: return .green
        case .waiting: return .orange
        case .idle: return .blue
        case .stuck: return .red
        case .unknown: return .gray
        }
    }

    private enum Metrics {
        static let rowSpacing: CGFloat = 10
        static let rowInnerSpacing: CGFloat = 3
        static let indicatorWidth: CGFloat = 18
        static let dotSize: CGFloat = 10
        static let dotTopPadding: CGFloat = 5
        static let exitedOpacity = 0.55
    }
}

// MARK: - Screen copy

private enum ScreenCopy {
    static let title = "会话"
    static let newSession = "新建会话"
    static let kill = "结束"
    static let addHost = "配对新主机"
    static let hostMenuFallback = "主机"
    static let notPairedTitle = "还没有配对的主机"
    static let notPairedHint = "先配对你电脑上的 web-terminal（扫码或手输地址），会话会出现在这里。"
    static let noSessionsTitle = "主机上没有运行中的会话"
    static let noSessionsHint = "新建一个会话开始工作；关掉 App 后会话仍会在主机上继续跑。"
    static let unknownDirectory = "未知目录"
    static let exitedTag = "已退出"
    static let pendingBadgeLabel = "等待审批"

    static func clientCount(_ count: Int) -> String {
        "\(count) 台设备在看"
    }
}