using System.Text.Json;
using System.Text.Json.Serialization;
using Fleet.Core;
using Fleet.Hosting;
using MoShiro.Measurement;
using MoShiro.Protocol;

namespace MoShiro.Agent;

/// <summary>
/// Native supervisor bridge: writes only fixed wake-up flags and a health beacon in tmpfs.
/// Never downloads, installs, verifies releases, or executes commands. The root-owned host
/// updater independently fetches and verifies its locally configured release feed.
/// </summary>
public sealed class OpenWrtUpdater
{
    private readonly ConfigStore _runtime;
    private readonly string _statusPath;
    private readonly TimeProvider _time;
    private readonly INodeLog _log;

    public OpenWrtUpdater(string runtimeDirectory, string statusPath, TimeProvider time, INodeLog log)
    {
        _runtime = new ConfigStore(runtimeDirectory);
        _statusPath = statusPath;
        _time = time;
        _log = log;
    }

    public static OpenWrtUpdater? FromEnvironment(TimeProvider time, INodeLog log) =>
        Environment.GetEnvironmentVariable(RestartUpdater.EnvironmentVariable) == "openwrt"
            ? new OpenWrtUpdater("/var/run/moshiro-agent", "/var/run/moshiro-update/status.json", time, log)
            : null;

    public void Offer() => Signal("check.request");

    public void RequestApply() => Signal("apply.request");

    private void Signal(string fileName)
    {
        try
        {
            _runtime.Write(fileName, "check"u8.ToArray());
        }
        catch (Exception ex) when (ex is IOException or UnauthorizedAccessException)
        {
            _log.Warn("could not signal the native updater", ("err", ex.Message));
        }
    }

    /// <summary>Called by the Fleet heartbeat: evidence that this version reached Backend.</summary>
    public UpdateStatus? Status()
    {
        try
        {
            var health = new OpenWrtHealth(BuildInfo.Version, Environment.ProcessId, _time.GetUtcNow().ToUnixTimeSeconds());
            _runtime.Write("health.json", JsonSerializer.SerializeToUtf8Bytes(health, AgentConfigContext.Default.OpenWrtHealth));
            if (!File.Exists(_statusPath) || new FileInfo(_statusPath).Length > 8192)
            {
                return null;
            }

            return JsonSerializer.Deserialize(File.ReadAllBytes(_statusPath), MoShiroJsonContext.Default.UpdateStatus);
        }
        catch (Exception ex) when (ex is IOException or UnauthorizedAccessException or JsonException)
        {
            _log.Warn("could not read native update status", ("err", ex.Message));
            return null;
        }
    }
}

public sealed record OpenWrtHealth(
    [property: JsonPropertyName("version")] string Version,
    [property: JsonPropertyName("pid")] int Pid,
    [property: JsonPropertyName("at")] long At);