namespace MoonlightServers.Daemon.Helpers;

/// <summary>
/// Reads Linux system metrics directly from the <c>/proc</c> and <c>/sys</c>
/// pseudo-filesystems
/// </summary>
public static partial class SystemMetrics
{
    public record SystemSnapshot(
        CpuSnapshot Cpu,
        MemoryInfo Memory,
        IReadOnlyList<DiskInfo> Disks,
        IReadOnlyList<NetworkInterfaceInfo> Network,
        TimeSpan Uptime
    );

    /// <summary>
    /// Collects a full system snapshot. The method waits <paramref name="sampleIntervalMs"/>
    /// milliseconds between the two samples required to compute CPU and network rates.
    /// All other reads happen in parallel during the second sampling window.
    /// </summary>
    /// <param name="sampleIntervalMs">
    /// Interval between rate-measurement samples in milliseconds.
    /// Larger values yield smoother CPU and network averages. Defaults to <c>500</c>.
    /// </param>
    /// <returns>A fully populated <see cref="SystemSnapshot"/>.</returns>
    public static async Task<SystemSnapshot> ReadAllAsync(int sampleIntervalMs = 500)
    {
        // First samples — must complete before the delay.
        var cpuSample1Task = ReadRawCpuStatsAsync();
        var netSample1Task = ReadRawNetStatsAsync();
        await Task.WhenAll(cpuSample1Task, netSample1Task);

        await Task.Delay(sampleIntervalMs);

        // Second samples + all independent reads run concurrently.
        var cpuSample2Task = ReadRawCpuStatsAsync();
        var netSample2Task = ReadRawNetStatsAsync();
        var memTask = ReadMemoryAsync();
        var diskTask = ReadDisksAsync();
        var uptimeTask = ReadUptimeAsync();
        var cpuNameTask = ReadCpuModelNameAsync();

        await Task.WhenAll(cpuSample2Task, netSample2Task, memTask, diskTask, uptimeTask, cpuNameTask);

        var cpu = ComputeCpuUsage(cpuNameTask.Result, cpuSample1Task.Result, cpuSample2Task.Result);
        var network = ComputeNetworkRates(netSample1Task.Result, netSample2Task.Result, sampleIntervalMs / 1000.0);

        return new SystemSnapshot(cpu, memTask.Result, diskTask.Result, network, uptimeTask.Result);
    }

    // Uptime
    private static async Task<TimeSpan> ReadUptimeAsync()
    {
        var text = await File.ReadAllTextAsync("/proc/uptime");
        var seconds = double.Parse(text.Split(' ')[0], System.Globalization.CultureInfo.InvariantCulture);
        return TimeSpan.FromSeconds(seconds);
    }
}