using System.Diagnostics;
using ClawdDotNet.Licensing;
using Deploymentcenter.Client;
using Microsoft.Extensions.Logging;

namespace ClawdDotNet.Manager;

/// <summary>#795: What the last update check found.</summary>
public sealed record UpdateStatus(
    string InstalledVersion,
    bool Available,
    string? LatestVersion,
    bool Critical,
    string? Notes,
    DateTimeOffset? CheckedAt,
    string? Problem,
    bool UnderSystemd);

/// <summary>#795: The outcome of asking for an update to be installed.</summary>
/// <param name="ShutdownFollows">The manager ends now; the update agent or systemd brings it back.</param>
public sealed record UpdateStart(bool Ok, string Message, bool ShutdownFollows = false);

/// <summary>
/// #795: Offering and installing an update from the web interface — until now only the desktop
/// window did that (<c>App.OfferUpdateAsync</c>), and every installation without a window was
/// updated by hand.
///
/// <para><b>In the manager, not the instance.</b> The package holds the manager and the instance
/// program together; the manager is the one process that can stop all instances first, so the
/// update agent does not write over files that running instances hold open.</para>
///
/// <para><b>Two ways, chosen by how the manager runs</b> (Deploymentcenter
/// SETUP_INTEGRATION_GUIDE §4A):</para>
/// <list type="bullet">
/// <item><b>Without systemd</b> the update agent waits for the manager to end
/// (<c>--wait-for-pid</c>) and starts it again afterwards (<c>--restart</c>).</item>
/// <item><b>Under systemd</b> a restart by the agent would be a second manager next to the
/// service. Instead a oneshot unit stops the service, runs the agent and starts the service
/// (<c>deploy/systemd/clawddotnet-update.service</c>); the manager only triggers it. Without
/// the unit nothing is stopped for nothing: the instances come back up and the answer says
/// what is missing.</item>
/// </list>
/// </summary>
public sealed class ManagerUpdates
{
    /// <summary>The oneshot unit that stops, updates and starts the manager service.</summary>
    public const string UpdateUnit = "clawddotnet-update.service";

    private readonly ManagerCore _manager;
    private readonly ILogger _logger;
    private readonly string _version;
    private readonly Func<CancellationToken, Task<UpdateCheckResult>> _check;
    private readonly Func<string?> _launchAgent;
    private readonly Func<string[], (int ExitCode, string Output)> _systemctl;
    private readonly bool _underSystemd;
    private readonly SemaphoreSlim _once = new(1, 1);

    private UpdateStatus _status;

    /// <summary>Raised after a successful hand-over: the caller ends the manager.</summary>
    public event Action? ShutdownRequested;

    public ManagerUpdates(ManagerCore manager, string version, ILogger logger)
        : this(manager, version, logger,
            check: null, launchAgent: null, systemctl: null,
            underSystemd: OperatingSystem.IsLinux() && !string.IsNullOrEmpty(Environment.GetEnvironmentVariable("INVOCATION_ID")))
    {
    }

    /// <summary>For tests: server, agent and systemctl given, not real.</summary>
    internal ManagerUpdates(
        ManagerCore manager, string version, ILogger logger,
        Func<CancellationToken, Task<UpdateCheckResult>>? check,
        Func<string?>? launchAgent,
        Func<string[], (int, string)>? systemctl,
        bool underSystemd)
    {
        _manager = manager;
        _version = version;
        _logger = logger;
        _underSystemd = underSystemd;
        _check = check ?? CheckWithServerAsync;
        _launchAgent = launchAgent ?? LaunchAgent;
        _systemctl = systemctl ?? RunSystemctl;
        _status = new UpdateStatus(version, false, null, false, null, null, null, underSystemd);
    }

    public UpdateStatus Status => _status;

    public async Task<UpdateStatus> CheckAsync(CancellationToken ct = default)
    {
        if (string.IsNullOrWhiteSpace(_manager.Settings.LicenseKey))
            return _status = _status with { Problem = "Without a license key there is no access to the releases.", CheckedAt = DateTimeOffset.Now };

        try
        {
            var result = await _check(ct).ConfigureAwait(false);

            // A 401 says something about the license, not the network.
            var problem = result.Unauthorized
                ? "The release store refused the license key."
                : result.Error is not null ? $"Update check failed: {result.Message}" : null;

            return _status = new UpdateStatus(
                _version, problem is null && result.UpdateAvailable, result.LatestRelease?.Version,
                result.IsCritical, result.LatestRelease?.Changelog, DateTimeOffset.Now, problem, _underSystemd);
        }
        catch (Exception ex) when (ex is not OperationCanceledException)
        {
            _logger.LogWarning(ex, "Update check failed");
            return _status = _status with { Problem = $"Update check failed: {ex.Message}", CheckedAt = DateTimeOffset.Now };
        }
    }

    /// <summary>
    /// Stops every instance in order and hands over to the update agent (or the update unit).
    /// On any failure before the hand-over, the instances that ran are started again.
    /// </summary>
    public async Task<UpdateStart> InstallAsync()
    {
        if (!await _once.WaitAsync(0).ConfigureAwait(false))
            return new UpdateStart(false, "An update is already being started.");

        try
        {
            if (string.IsNullOrWhiteSpace(_manager.Settings.LicenseKey))
                return new UpdateStart(false, "Without a license key the update agent cannot fetch the release.");

            if (_underSystemd && _systemctl(["--user", "cat", UpdateUnit]).ExitCode != 0)
            {
                return new UpdateStart(false,
                    $"The manager runs under systemd, but the unit {UpdateUnit} is not installed. "
                    + "Install it from deploy/systemd (see docs/InstanceSetupGuide.md) — nothing was stopped.");
            }

            // Which ones ran, so a failed hand-over can bring exactly those back.
            var running = _manager.Instances.Instances
                .Where(i => i.Condition is InstanceCondition.Running or InstanceCondition.Silent)
                .Select(i => i.Directory)
                .ToList();

            // Without the request's token: a closed browser must not leave half the instances stopped.
            await _manager.Instances.StopAllAsync("Update wird eingespielt", CancellationToken.None).ConfigureAwait(false);

            string? problem;
            if (_underSystemd)
            {
                // --no-block: the unit stops this very service; waiting for it would wait for our own end.
                var (exit, output) = _systemctl(["--user", "start", "--no-block", UpdateUnit]);
                problem = exit == 0 ? null : $"systemctl could not start {UpdateUnit}: {output.Trim()}";
            }
            else
            {
                problem = _launchAgent();
            }

            if (problem is not null)
            {
                _logger.LogWarning("Update not started: {Problem} - restarting instances", problem);
                foreach (var directory in running)
                    await _manager.StartInstanceAsync(directory, CancellationToken.None).ConfigureAwait(false);
                return new UpdateStart(false, problem);
            }

            _logger.LogInformation("Update handed over ({Way}); the manager ends now.", _underSystemd ? UpdateUnit : "update-agent");

            if (!_underSystemd)
                ShutdownRequested?.Invoke();

            return new UpdateStart(true, _underSystemd
                ? "Update started. The service is stopped, updated and started again; this page reconnects in a minute or two."
                : "Update started. The manager ends now and is started again by the update agent.",
                ShutdownFollows: true);
        }
        finally
        {
            _once.Release();
        }
    }

    private Task<UpdateCheckResult> CheckWithServerAsync(CancellationToken ct)
        => new UpdateClient().CheckForUpdateAsync(
            _manager.Settings.DeploymentcenterUrl, LicenseInfo.ProductSlug, _version,
            _manager.Settings.UpdateChannel,
            credentials: ReleaseCredentials.FromLicenseKey(_manager.Settings.LicenseKey),
            cancellationToken: ct);

    /// <returns>The reason it did not start, or <c>null</c>.</returns>
    private string? LaunchAgent()
    {
        if (UpdateClient.ResolveAgentPath() is not { } agent)
            return "The update agent was not found next to the manager; the installation package brings it.";

        try
        {
            // The key goes through the environment, never argv (the SDK takes care of that).
            // Unsigned releases are not installed: the hash comes from the same source as the
            // package, so whoever swaps one swaps both.
            return UpdateClient.LaunchUpdateAgent(
                agentPath: agent,
                projectId: LicenseInfo.ProductSlug,
                channel: _manager.Settings.UpdateChannel,
                action: "update",
                version: "latest",
                exitCurrentApp: false,
                currentVersion: _version,
                waitForCurrentProcess: true,
                licenseKey: _manager.Settings.LicenseKey,
                waitTimeoutSeconds: 120,
                requireSignature: true)
                ? null
                : "The update agent could not be started.";
        }
        catch (Exception ex)
        {
            return $"The update agent could not be started: {ex.Message}";
        }
    }

    private static (int, string) RunSystemctl(string[] args)
    {
        try
        {
            var start = new ProcessStartInfo("systemctl") { RedirectStandardOutput = true, RedirectStandardError = true };
            foreach (var a in args) start.ArgumentList.Add(a);
            using var p = Process.Start(start)!;
            var output = p.StandardOutput.ReadToEnd() + p.StandardError.ReadToEnd();
            p.WaitForExit(30_000);
            return (p.HasExited ? p.ExitCode : -1, output);
        }
        catch (Exception ex)
        {
            return (-1, ex.Message);
        }
    }
}