using WxAgent.Core;
using WxAgent.Service;
using WxAgent.Windows;

namespace WxAgent.Host;

public sealed class WindowsAgentBackend(AccountBindingStore bindings, ServiceOptions options) : IAgentBackend, IAgentEventSource, IRemoteDataCollector
{
    private readonly bool validationOperationsEnabled = options.EnableValidationOperations;
    private readonly bool listenerEventsEnabled = options.EnableListenerEvents;
    private readonly SemaphoreSlim bindingGate = new(1, 1);
    private readonly DatabaseMessageSyncCollector databaseSyncCollector = new(null, options.DataSyncBatchLimit, options.DataSyncOverlapRows);

    public IReadOnlyList<AgentCapability> Capabilities =>
    [
        new("agent-status", true, true, true, false, false, "read", false, 30, null, ["docs/validation/WebUI-MCP-single-client-2026-09-19.md"], "4.1.13.65"),
        new("agent-diagnose", true, true, true, false, false, "read", false, 30, null, ["docs/validation/WebUI-MCP-single-client-2026-09-19.md"], "4.1.13.65"),
        new("accounts-list", true, true, true, false, false, "read", false, 30, null, ["docs/validation/WebUI-MCP-single-client-2026-09-19.md"], "4.1.13.65"),
        new("account-binding", true, false, true, true, true, "manage", false, 30, "Auto-binds a unique database/UI identity match; manual binding remains available as fallback.", ["docs/WebUI-MCP-开发计划.md"]),
        new("sessions-list", true, true, true, true, false, "read", false, 30, null, ["docs/validation/WebUI-MCP-single-client-2026-09-19.md"], "4.1.13.65"),
        new("sessions-search", true, true, true, true, false, "read", false, 30, null, ["docs/validation/WebUI-MCP-single-client-2026-09-19.md"], "4.1.13.65"),
        new("session-current", true, true, true, true, false, "read", false, 30, null, ["docs/validation/WebUI-MCP-single-client-2026-09-19.md"], "4.1.13.65"),
        new("sessions-scroll", true, false, validationOperationsEnabled, true, false, "manage", false, 30,
            validationOperationsEnabled ? null : "Validation operations are disabled for this service session.", ["Controlled validation mode."], "4.1.13.65"),
        new("session-open", true, false, validationOperationsEnabled, true, true, "manage", false, 30,
            validationOperationsEnabled ? null : "Validation operations are disabled for this service session.", ["Controlled validation mode."], "4.1.13.65"),
        new("messages-read", true, true, true, true, false, "read", false, 30, null, ["docs/validation/WebUI-MCP-single-client-2026-09-19.md"], "4.1.13.65"),
        new("contacts-list", true, true, true, false, false, "read", false, 30, null, ["docs/validation/WebUI-MCP-single-client-2026-09-19.md"], "4.1.13.65"),
        new("db-messages", true, true, true, false, false, "read", false, 30, null,
            ["docs/validation/WxAgent-会话消息同步-P4-验收记录.md", "docs/validation/WxAgent-会话消息同步-P4-live-evidence.json"], "4.1.13.65"),
        new("db-merged", true, true, true, false, false, "read", false, 30, null,
            ["docs/validation/WxAgent-会话消息同步-P4-验收记录.md", "docs/validation/WxAgent-会话消息同步-P4-live-evidence.json"], "4.1.13.65"),
        new("group-members", true, true, true, false, false, "read", false, 30, null, ["docs/validation/WebUI-MCP-single-client-2026-09-19.md"], "4.1.13.65"),
        new("listener-events", true, listenerEventsEnabled, listenerEventsEnabled, true, false, "read", false, 30,
            listenerEventsEnabled ? null : "Background UI listener is disabled; enable it explicitly in the Tray settings window.", ["docs/validation/WebUI-MCP-single-client-2026-09-19.md"], "4.1.13.65"),
        new("send-text", true, true, validationOperationsEnabled, true, true, "write", true, 30,
            validationOperationsEnabled ? null : "Validation operations are disabled for this service session.", ["docs/validation/WebUI-MCP-single-client-2026-09-19.md"], "4.1.13.65"),
        new("broadcast-text", true, true, validationOperationsEnabled, true, true, "write", true, 300,
            validationOperationsEnabled ? null : "Validation operations are disabled for this service session.", ["docs/validation/WebUI-MCP-single-client-2026-09-19.md"], "4.1.13.65"),
        new("group-at-all", true, false, false, true, true, "write", true, 30,
            "No group-at-all operation is registered; validate group targets through confirmed send-text tasks.", []),
        new("next-unread", false, false, false, true, false, "read", false, 30,
            "Deferred by docs/PENDING.md.", [])
    ];

    public async IAsyncEnumerable<AgentEvent> ListenAsync([System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken)
    {
        if (!listenerEventsEnabled)
        {
            await Task.Delay(Timeout.InfiniteTimeSpan, cancellationToken);
            yield break;
        }

        var active = bindings.ReadAll();
        if (active.Count != 1)
        {
            await Task.Delay(Timeout.InfiniteTimeSpan, cancellationToken);
            yield break;
        }
        var binding = active[0];
        using var scope = WechatChatClient.UseWindowTarget(binding.ProcessId, binding.WindowHandle);
        if (string.IsNullOrWhiteSpace(binding.WechatId) && string.IsNullOrWhiteSpace(binding.Nickname))
            throw new ServiceException("AccountBindingStale", 409, "The persisted account binding has no verified identity; bind the account again.");
        var sessions = (await WechatChatClient.ListVisibleSessionsAsync(cancellationToken))
            .Where(session => string.Equals(session.Name, WechatLocators.FileTransferAssistant, StringComparison.Ordinal)
                && !string.IsNullOrWhiteSpace(session.AutomationId))
            .ToArray();
        if (sessions.Length != 1)
            throw new ServiceException("ChatIdentityUnconfirmed", 409, "The listener chat identity could not be uniquely confirmed.");
        var chatId = sessions[0].AutomationId;
        var accountTag = Convert.ToHexString(System.Security.Cryptography.SHA256.HashData(System.Text.Encoding.UTF8.GetBytes(binding.AccountId)))[..16].ToLowerInvariant();
        var checkpoint = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "WxAgent", $"listener-{accountTag}.json");
        while (!cancellationToken.IsCancellationRequested)
        {
            await foreach (var item in WechatChatClient.ListenEventsAsync(TimeSpan.FromMinutes(5), checkpoint, cancellationToken,
                session: WechatLocators.FileTransferAssistant))
            {
                var eventType = item.Kind == MessageEventKind.MessageReceived ? "message" : "listener.reconnected";
                yield return new AgentEvent(item.EventId, binding.AccountId, item.Session,
                    eventType, item.Message is null ? "listener state" : item.Message.Type.ToString(), item.ObservedAt,
                    chatId, ReportingChatType.Private, item.Message?.Text);
            }
        }
    }

    private static bool BindingMatches(AccountBinding binding, WechatAccountSnapshot current) =>
        !string.IsNullOrWhiteSpace(binding.WechatId)
            ? string.Equals(binding.WechatId, current.WechatId, StringComparison.OrdinalIgnoreCase)
            : string.Equals(binding.Nickname, current.DisplayName, StringComparison.Ordinal);

    public Task<IReadOnlyList<AccountInfo>> AccountsAsync(CancellationToken cancellationToken) =>
        AccountsAsync(cancellationToken, refreshUiIdentity: true);

    public async Task<IReadOnlyList<AccountInfo>> AccountsAsync(CancellationToken cancellationToken, bool refreshUiIdentity)
    {
        var targets = await ReadUiTargetsAsync(cancellationToken, refreshUiIdentity);
        var accounts = await ReadDatabaseAccountsAsync(cancellationToken);
        if (refreshUiIdentity)
            await AutoBindMatchesAsync(accounts, targets, cancellationToken);
        var current = bindings.ReadAll();
        var singleBoundTarget = !refreshUiIdentity && current.Count == 1 && targets.Count == 1;
        var live = current.Where(binding => targets.Any(target =>
                (target.ProcessId == binding.ProcessId && target.WindowHandle == binding.WindowHandle &&
                 (!refreshUiIdentity || string.IsNullOrWhiteSpace(target.WechatId) && string.IsNullOrWhiteSpace(target.Nickname) ||
                  BindingMatches(binding, new WechatAccountSnapshot(target.Nickname ?? string.Empty, target.WechatId)))) ||
                singleBoundTarget))
            .Select(binding => binding.AccountId)
            .ToHashSet(StringComparer.OrdinalIgnoreCase);
        return accounts.Select(account =>
        {
            var binding = bindings.Get(account.AccountId);
            var isLive = binding is not null && live.Contains(binding.AccountId);
            return new AccountInfo(account.AccountId, account.Identity?.Nickname, account.Identity?.WechatId, null,
                account.AccountId, isLive, binding, binding is null ? "Unbound" : isLive ? "Bound" : "Stale");
        }).ToArray();
    }

    public async Task<IReadOnlyList<UiTargetInfo>> UiTargetsAsync(CancellationToken cancellationToken)
    {
        var targets = await ReadUiTargetsAsync(cancellationToken, true);
        var accounts = await ReadDatabaseAccountsAsync(cancellationToken);
        await AutoBindMatchesAsync(accounts, targets, cancellationToken);
        var bound = bindings.ReadAll().Select(binding => (binding.ProcessId, binding.WindowHandle))
            .ToHashSet(new BindingTargetComparer());
        return targets.Select(target => target with
        {
            IsBound = bound.Contains((target.ProcessId, target.WindowHandle))
        }).ToArray();
    }

    private async Task<IReadOnlyList<UiTargetInfo>> ReadUiTargetsAsync(CancellationToken cancellationToken, bool readIdentity)
    {
        var bound = bindings.ReadAll().Select(binding => (binding.ProcessId, binding.WindowHandle)).ToHashSet(new BindingTargetComparer());
        var targets = new List<UiTargetInfo>();
        foreach (var window in WechatChatClient.InspectMainWindows().Where(window => window.Visible && !window.Minimized))
        {
            cancellationToken.ThrowIfCancellationRequested();
            string? wechatId = null;
            string? nickname = null;
            if (readIdentity)
            {
                try
                {
                    using var scope = WechatChatClient.UseWindowTarget(window.ProcessId, window.Handle);
                    var identity = await WechatChatClient.GetMyInfoAsync(cancellationToken);
                    wechatId = identity.WechatId;
                    nickname = identity.DisplayName;
                }
                catch (WxAgentException) { }
            }
            targets.Add(new UiTargetInfo(TargetId(window.ProcessId, window.Handle), window.ProcessId, window.Handle,
                window.Title, wechatId, nickname, bound.Contains((window.ProcessId, window.Handle))));
        }
        return targets;
    }

    public async Task<AccountBinding> BindAccountAsync(string accountId, string targetId, CancellationToken cancellationToken)
    {
        if (!TryParseTargetId(targetId, out var processId, out var windowHandle))
            throw new ServiceException("InvalidTarget", 400, "targetId is not a current WeChat window target.");
        var target = (await ReadUiTargetsAsync(cancellationToken, true)).SingleOrDefault(x => x.TargetId == targetId);
        if (target is null) throw new ServiceException("TargetUnavailable", 409, "The selected WeChat window is not available.");

        var account = await WechatContactDbReader.LoadAccountAsync(accountId, cancellationToken: cancellationToken);
        WechatAccountSnapshot ui;
        if (!string.IsNullOrWhiteSpace(target.WechatId) || !string.IsNullOrWhiteSpace(target.Nickname))
            ui = new WechatAccountSnapshot(target.Nickname ?? string.Empty, target.WechatId);
        else
        {
            using var scope = WechatChatClient.UseWindowTarget(processId, windowHandle);
            ui = await WechatChatClient.GetMyInfoAsync(cancellationToken);
        }
        var databaseIdentity = await TryReadDatabaseIdentityAsync(account, cancellationToken)
            ?? await TryReadDatabaseIdentityAsync(account, ui, cancellationToken)
            ?? throw new ServiceException("AccountIdentityUnavailable", 409, "The selected database account identity could not be read safely.");
        var match = AccountBindingMatcher.Match(new UiAccountIdentity(ui.WechatId, ui.DisplayName), [databaseIdentity]);
        if (!match.IsMatched || !string.Equals(match.AccountId, account.AccountRootFingerprint, StringComparison.OrdinalIgnoreCase))
            throw new ServiceException("AccountBindingMismatch", 409, "The selected WeChat window does not match the selected database account.");

        await bindingGate.WaitAsync(cancellationToken);
        try
        {
            var current = bindings.ReadAll();
            var accountMatches = current.Where(x => string.Equals(x.AccountId, account.AccountRootFingerprint, StringComparison.OrdinalIgnoreCase)).ToArray();
            if (accountMatches.Length > 1)
                throw new ServiceException("BindingAmbiguous", 409, "The persisted account binding is ambiguous; remove account-bindings.json and bind again.");
            var accountBinding = accountMatches.SingleOrDefault();
            if (accountBinding is not null && (accountBinding.ProcessId != processId || accountBinding.WindowHandle != windowHandle))
                throw new ServiceException("AccountAlreadyBound", 409, "The account is already bound to another WeChat window; unbind it first.");
            var targetMatches = current.Where(x => x.ProcessId == processId && x.WindowHandle == windowHandle).ToArray();
            if (targetMatches.Length > 1)
                throw new ServiceException("BindingAmbiguous", 409, "The persisted window binding is ambiguous; remove account-bindings.json and bind again.");
            var targetBinding = targetMatches.SingleOrDefault();
            if (targetBinding is not null && !string.Equals(targetBinding.AccountId, account.AccountRootFingerprint, StringComparison.OrdinalIgnoreCase))
                throw new ServiceException("TargetAlreadyBound", 409, "The selected WeChat window is already bound to another account.");

            var binding = new AccountBinding(account.AccountRootFingerprint, processId, windowHandle,
                ui.WechatId, ui.DisplayName ?? string.Empty, DateTimeOffset.UtcNow);
            bindings.Replace(current.Where(x => !string.Equals(x.AccountId, binding.AccountId, StringComparison.OrdinalIgnoreCase)).Append(binding));
            return binding;
        }
        finally { bindingGate.Release(); }
    }

    public async Task UnbindAccountAsync(string accountId, CancellationToken cancellationToken)
    {
        await bindingGate.WaitAsync(cancellationToken);
        try { bindings.Remove(accountId); }
        finally { bindingGate.Release(); }
    }

    private static string TargetId(int processId, long windowHandle) =>
        $"{processId.ToString(System.Globalization.CultureInfo.InvariantCulture)}:{windowHandle.ToString(System.Globalization.CultureInfo.InvariantCulture)}";

    private static bool TryParseTargetId(string targetId, out int processId, out long windowHandle)
    {
        processId = 0;
        windowHandle = 0;
        var parts = targetId.Split(':', 2);
        return parts.Length == 2 && int.TryParse(parts[0], System.Globalization.NumberStyles.None,
            System.Globalization.CultureInfo.InvariantCulture, out processId) &&
            long.TryParse(parts[1], System.Globalization.NumberStyles.None, System.Globalization.CultureInfo.InvariantCulture, out windowHandle) &&
            processId > 0 && windowHandle > 0;
    }

    private async Task<IReadOnlyList<DatabaseAccount>> ReadDatabaseAccountsAsync(CancellationToken cancellationToken)
    {
        var roots = WechatDatabaseDiscovery.FindAccountRoots(cancellationToken: cancellationToken);
        var accounts = new List<DatabaseAccount>(roots.Count);
        foreach (var root in roots)
        {
            DatabaseAccountIdentity? identity = null;
            try
            {
                var account = await WechatContactDbReader.LoadAccountAsync(root.Fingerprint, cancellationToken: cancellationToken);
                identity = await TryReadDatabaseIdentityAsync(account, cancellationToken);
            }
            catch (WxAgentException) { }
            accounts.Add(new(root.Fingerprint, identity));
        }
        return accounts;
    }

    private async Task AutoBindMatchesAsync(IReadOnlyList<DatabaseAccount> accounts,
        IReadOnlyList<UiTargetInfo> targets, CancellationToken cancellationToken)
    {
        if (accounts.All(account => account.Identity is null) || targets.Count == 0) return;
        await bindingGate.WaitAsync(cancellationToken);
        try
        {
            var current = bindings.ReadAll().ToList();
            var changed = false;
            foreach (var target in targets.Where(target => !string.IsNullOrWhiteSpace(target.WechatId) || !string.IsNullOrWhiteSpace(target.Nickname)))
            {
                var existing = current.FirstOrDefault(binding => binding.ProcessId == target.ProcessId && binding.WindowHandle == target.WindowHandle);
                var available = accounts.Where(account => account.Identity is not null &&
                        (existing is not null && string.Equals(existing.AccountId, account.AccountId, StringComparison.OrdinalIgnoreCase) ||
                         !current.Any(binding => string.Equals(binding.AccountId, account.AccountId, StringComparison.OrdinalIgnoreCase))))
                    .Select(account => account.Identity!)
                    .ToArray();
                var match = AccountBindingMatcher.Match(new UiAccountIdentity(target.WechatId, target.Nickname), available);
                if (!match.IsMatched) continue;
                var identity = available.Single(account => string.Equals(account.AccountId, match.AccountId, StringComparison.OrdinalIgnoreCase));
                var binding = new AccountBinding(identity.AccountId, target.ProcessId, target.WindowHandle,
                    target.WechatId, target.Nickname ?? string.Empty, existing?.BoundAt ?? DateTimeOffset.UtcNow);
                if (existing is null)
                {
                    current.Add(binding);
                    changed = true;
                }
                else if (existing.AccountId.Equals(binding.AccountId, StringComparison.OrdinalIgnoreCase) &&
                    (!string.Equals(existing.WechatId, binding.WechatId, StringComparison.OrdinalIgnoreCase) ||
                     !string.Equals(existing.Nickname, binding.Nickname, StringComparison.Ordinal)))
                {
                    current[current.IndexOf(existing)] = binding;
                    changed = true;
                }
            }
            if (changed) bindings.Replace(current);
        }
        finally { bindingGate.Release(); }
    }

    private static async Task<DatabaseAccountIdentity?> TryReadDatabaseIdentityAsync(AccountKeySet account,
        CancellationToken cancellationToken)
    {
        try { return await WechatContactDbReader.ReadAccountIdentityAsync(account, cancellationToken); }
        catch (WxAgentException) { return null; }
    }

    private static async Task<DatabaseAccountIdentity?> TryReadDatabaseIdentityAsync(AccountKeySet account,
        WechatAccountSnapshot ui, CancellationToken cancellationToken)
    {
        try
        {
            if (!string.IsNullOrWhiteSpace(ui.WechatId))
            {
                var page = await WechatContactDbReader.ReadPageAsync(account, 10000, 0, ui.WechatId, false, cancellationToken);
                var exact = page.Contacts.Where(x => string.Equals(x.Username, ui.WechatId, StringComparison.OrdinalIgnoreCase)).ToArray();
                if (exact.Length == 1)
                    return new DatabaseAccountIdentity(account.AccountRootFingerprint, exact[0].Username, exact[0].DisplayName);
            }
            if (!string.IsNullOrWhiteSpace(ui.DisplayName))
            {
                var page = await WechatContactDbReader.ReadPageAsync(account, 10000, 0, ui.DisplayName, false, cancellationToken);
                var exact = page.Contacts.Where(x => string.Equals(x.DisplayName, ui.DisplayName, StringComparison.Ordinal) ||
                    string.Equals(x.Remark, ui.DisplayName, StringComparison.Ordinal)).ToArray();
                if (exact.Length == 1)
                    return new DatabaseAccountIdentity(account.AccountRootFingerprint, exact[0].Username, exact[0].DisplayName);
            }
            return null;
        }
        catch (WxAgentException) { return null; }
    }

    private sealed record DatabaseAccount(string AccountId, DatabaseAccountIdentity? Identity);

    private sealed class BindingTargetComparer : IEqualityComparer<(int ProcessId, long WindowHandle)>
    {
        public bool Equals((int ProcessId, long WindowHandle) x, (int ProcessId, long WindowHandle) y) => x == y;
        public int GetHashCode((int ProcessId, long WindowHandle) value) => HashCode.Combine(value.ProcessId, value.WindowHandle);
    }

    public async Task<IReadOnlyList<SessionInfo>> SessionsAsync(CancellationToken cancellationToken)
    {
        var sessions = await WechatChatClient.ListVisibleSessionsAsync(cancellationToken);
        return sessions.Select(s => new SessionInfo(s.Name, s.AutomationId, s.IsCurrent)).ToArray();
    }

    public Task<IReadOnlyList<SessionInfo>> SessionsAsync(string? accountId, CancellationToken cancellationToken) =>
        ForAccountAsync(accountId, cancellationToken, () => SessionsAsync(cancellationToken));

    public async Task<IReadOnlyList<SessionSearchInfo>> SearchSessionsAsync(string query, bool exactOnly, CancellationToken cancellationToken)
    {
        var results = await WechatChatClient.SearchSessionsAsync(query, exactOnly, cancellationToken);
        return results.Select(s => new SessionSearchInfo(s.Name, s.AutomationId, s.IsExactMatch)).ToArray();
    }

    public Task<IReadOnlyList<SessionSearchInfo>> SearchSessionsAsync(string? accountId, string query, bool exactOnly, CancellationToken cancellationToken) =>
        ForAccountAsync(accountId, cancellationToken, () => SearchSessionsAsync(query, exactOnly, cancellationToken));

    public async Task<SessionInfo?> CurrentSessionAsync(CancellationToken cancellationToken)
    {
        var current = await WechatChatClient.GetCurrentSessionAsync(cancellationToken);
        return current is null ? null : new SessionInfo(current.Name, current.AutomationId, true);
    }

    public Task<SessionInfo?> CurrentSessionAsync(string? accountId, CancellationToken cancellationToken) =>
        ForAccountAsync(accountId, cancellationToken, () => CurrentSessionAsync(cancellationToken));

    public async Task<SessionInfo> OpenSessionAsync(string automationId, CancellationToken cancellationToken)
    {
        var matches = (await WechatChatClient.ListVisibleSessionsAsync(cancellationToken)).Where(s => s.AutomationId == automationId).ToArray();
        if (matches.Length != 1) throw new ServiceException(matches.Length == 0 ? "NotFound" : "AmbiguousTarget", 409, "AutomationId is not unique.");
        await WechatChatClient.OpenSessionAsync(matches[0].Name, cancellationToken, automationId);
        return new SessionInfo(matches[0].Name, matches[0].AutomationId, true);
    }

    public Task<SessionInfo> OpenSessionAsync(string? accountId, string automationId, CancellationToken cancellationToken) =>
        ForAccountAsync(accountId, cancellationToken, () => OpenSessionAsync(automationId, cancellationToken), validateIdentity: true);

    public async Task<SessionViewportInfo> ScrollSessionsAsync(string direction, int pages, CancellationToken cancellationToken)
    {
        var result = await WechatChatClient.ScrollSessionsAsync(direction == "up" ? WechatScrollDirection.Up : WechatScrollDirection.Down, pages, cancellationToken);
        return new SessionViewportInfo(result.Scrolls, result.ViewportChanged,
            result.Sessions.Select(s => new SessionInfo(s.Name, s.AutomationId, s.IsCurrent)).ToArray());
    }

    public Task<SessionViewportInfo> ScrollSessionsAsync(string? accountId, string direction, int pages, CancellationToken cancellationToken) =>
        ForAccountAsync(accountId, cancellationToken, () => ScrollSessionsAsync(direction, pages, cancellationToken), validateIdentity: true);

    public async Task<IReadOnlyList<MessageInfo>> MessagesAsync(string? session, bool includeContent, CancellationToken cancellationToken)
    {
        if (!string.IsNullOrWhiteSpace(session))
        {
            var requestedName = session.StartsWith("session_item_", StringComparison.Ordinal)
                ? session["session_item_".Length..]
                : session;
            await WechatChatClient.OpenSessionAsync(requestedName, cancellationToken);
        }
        var messages = await WechatChatClient.ReadVisibleAsync(cancellationToken);
        return messages.Select(m => new MessageInfo(m.Fingerprint, m.Type.ToString(), m.Quote?.Sender,
            m.Text.Length > 160 ? m.Text[..160] : m.Text, includeContent ? m.Text : null)).ToArray();
    }

    public Task<IReadOnlyList<MessageInfo>> MessagesAsync(string? accountId, string? session, bool includeContent, CancellationToken cancellationToken) =>
        ForAccountAsync(accountId, cancellationToken, () => MessagesAsync(session, includeContent, cancellationToken));

    public async Task SendTextAsync(string accountId, string targetId, string text, CancellationToken cancellationToken)
    {
        await ForAccountAsync(accountId, cancellationToken, async () =>
        {
            var matches = (await WechatChatClient.ListVisibleSessionsAsync(cancellationToken))
                .Where(session => string.Equals(session.AutomationId, targetId, StringComparison.Ordinal)).ToArray();
            if (matches.Length != 1)
                throw new ServiceException(matches.Length == 0 ? "NotFound" : "AmbiguousTarget", 409, "The selected session is not unique or no longer visible.");
            await WechatChatClient.SendTextAsync(text, cancellationToken, matches[0].Name);
            return true;
        }, validateIdentity: true);
    }

    private async Task<T> ForAccountAsync<T>(string? accountId, CancellationToken cancellationToken, Func<Task<T>> action, bool validateIdentity = false)
    {
        if (string.IsNullOrWhiteSpace(accountId))
            throw new ServiceException("AccountIdRequired", 400, "accountId is required for every WeChat UI operation.");
        var matches = bindings.ReadAll().Where(x => string.Equals(x.AccountId, accountId, StringComparison.OrdinalIgnoreCase)).ToArray();
        if (matches.Length > 1)
            throw new ServiceException("BindingAmbiguous", 409, "The persisted account binding is ambiguous; bind state must be repaired before use.");
        var binding = matches.SingleOrDefault();
        if (binding is null)
            throw new ServiceException("AccountNotBound", 409, "The account is not explicitly bound to a WeChat window.");
        var target = (await ReadUiTargetsAsync(cancellationToken, false)).SingleOrDefault(x =>
            x.ProcessId == binding.ProcessId && x.WindowHandle == binding.WindowHandle);
        if (target is null)
            throw new ServiceException("AccountWindowUnavailable", 409, "The bound WeChat window is no longer available.");
        using var scope = WechatChatClient.UseWindowTarget(binding.ProcessId, binding.WindowHandle);
        if (validateIdentity)
        {
            var current = await WechatChatClient.GetMyInfoAsync(cancellationToken);
            var identityMatches = !string.IsNullOrWhiteSpace(binding.WechatId)
                ? string.Equals(binding.WechatId, current.WechatId, StringComparison.OrdinalIgnoreCase)
                : string.Equals(binding.Nickname, current.DisplayName, StringComparison.Ordinal);
            if (!identityMatches)
                throw new ServiceException("AccountBindingStale", 409, "The bound WeChat window identity changed; bind the account again.");
        }
        return await action();
    }

    public async Task<Page<ContactInfo>> ContactsAsync(string? accountId, string? contains, bool? groupsOnly, int limit, int offset, CancellationToken cancellationToken)
    {
        if (string.IsNullOrWhiteSpace(accountId))
            throw new ServiceException("AccountIdRequired", 400, "accountId is required for database contact operations.");
        var page = await WechatChatClient.GetContactsPageAsync(limit, offset, contains, groupsOnly, accountId, cancellationToken: cancellationToken);
        var items = page.Contacts.Select(c => new ContactInfo(c.Username, c.DisplayName, c.Remark, null)).ToArray();
        return new Page<ContactInfo>(items, limit, offset, page.HasMore, page.NextOffset);
    }

    public async Task<Page<GroupMemberInfo>> GroupMembersAsync(string accountId, string group, int limit, int offset, CancellationToken cancellationToken)
    {
        var page = await WechatChatClient.GetGroupMembersPageAsync(group, limit, offset, accountId, cancellationToken: cancellationToken);
        var items = page.Members.Select(m => new GroupMemberInfo(m.MemberId, m.Username, m.DisplayName, m.IsOwner)).ToArray();
        return new Page<GroupMemberInfo>(items, limit, offset, page.HasMore, page.NextOffset);
    }

    public Task<RemoteDataCollection> CollectAsync(
        string accountId,
        IReadOnlyList<RemoteReportingScope> scopes,
        RemoteDataSyncCheckpoint checkpoint,
        CancellationToken cancellationToken) =>
        databaseSyncCollector.CollectAsync(accountId, scopes, checkpoint, cancellationToken);

    public async Task<IReadOnlyList<DatabaseMessageInfo>> DatabaseMessagesAsync(string accountId, string chatId, int limit, long? localId, CancellationToken cancellationToken)
    {
        var account = await DatabaseKeyStore.LoadAsync(null, cancellationToken);
        var selected = account.SingleOrDefault(a => string.Equals(a.AccountRootFingerprint, accountId, StringComparison.OrdinalIgnoreCase))
            ?? throw new WxAgentException(WxAgentErrorCode.DatabaseKeyNotFound, "No verified database account matches the selected fingerprint.");
        var messages = await WechatMessageDbReader.ReadAsync(selected.AccountRootPath, selected.Databases, chatId, limit, cancellationToken, localId);
        return messages.Select(m => new DatabaseMessageInfo(m.LocalId, m.ServerId, m.ChatId, m.SenderWxId, m.SenderName, m.Type, m.Content, m.Timestamp, m.IsSelf)).ToArray();
    }

    public async Task<MergedMessageInfo> DatabaseMergedAsync(string accountId, string chatId, long localId, CancellationToken cancellationToken)
    {
        var account = await DatabaseKeyStore.LoadAsync(null, cancellationToken);
        var selected = account.SingleOrDefault(a => string.Equals(a.AccountRootFingerprint, accountId, StringComparison.OrdinalIgnoreCase))
            ?? throw new WxAgentException(WxAgentErrorCode.DatabaseKeyNotFound, "No verified database account matches the selected fingerprint.");
        var merged = await WechatMessageDbReader.ReadMergedAsync(selected.AccountRootPath, selected.Databases, chatId, localId, cancellationToken);
        var parent = merged.Parent;
        var messages = merged.Record.Messages.Select(m => new MergedMessagePart(m.SenderName, m.Text, m.Timestamp, m.Path, m.DataType)).ToArray();
        return new MergedMessageInfo(merged.DatabaseRelativePath,
            new DatabaseMessageInfo(parent.LocalId, parent.ServerId, parent.ChatId, parent.SenderWxId, parent.SenderName, parent.Type, parent.Content, parent.Timestamp, parent.IsSelf),
            merged.Record.Title, merged.Record.Description, messages);
    }

    public async Task<object> DiagnoseAsync(CancellationToken cancellationToken)
    {
        var result = await StatusAsync(cancellationToken);
        return new { diagnostic = true, redacted = true, result };
    }

    public Task<object> StatusAsync(CancellationToken cancellationToken)
    {
        var report = WechatDoctor.Run(cancellationToken);
        return Task.FromResult<object>(new
        {
            serviceOnline = true,
            // Process/window presence is availability; a changed control tree is a degraded UI state,
            // not a stopped WeChat process.
            wechatAvailable = report.Processes.Count > 0 && report.WindowFound,
            sessionAvailable = report.UserInteractive && report.InputDesktopAvailable,
            sessionLocked = report.Errors.Contains(WxAgentErrorCode.SessionLocked),
            report.WindowFound,
            errors = report.Errors.Select(e => e.ToString()),
            wechatVersions = report.Processes.Select(p => p.Version).Where(v => v is not null).Distinct(),
            activeAccountBound = bindings.ReadAll().Count != 0,
            defaultReadOnly = true
        });
    }
}