namespace MoonlightServers.Daemon.Helpers;

public partial class SystemMetrics
{
    public record CpuSnapshot(
        string ModelName,
        double TotalUsagePercent,
        IReadOnlyList<double> CoreUsagePercents
    );
    
    private record RawCpuLine(
        long User,
        long Nice,
        long System,
        long Idle,
        long Iowait,
        long Irq,
        long Softirq,
        long Steal
    );
    
    private static async Task<List<RawCpuLine>> ReadRawCpuStatsAsync()
    {
        var lines = await File.ReadAllLinesAsync("/proc/stat");
        var result = new List<RawCpuLine>();

        foreach (var line in lines)
        {
            // All cpu* lines appear at the top of the file; stop on the first non-cpu line.
            if (!line.StartsWith("cpu", StringComparison.Ordinal))
                break;

            var p = line.Split(' ', StringSplitOptions.RemoveEmptyEntries);
            if (p.Length < 8)
                continue;

            result.Add(new RawCpuLine(
                User: long.Parse(p[1]),
                Nice: long.Parse(p[2]),
                System: long.Parse(p[3]),
                Idle: long.Parse(p[4]),
                Iowait: long.Parse(p[5]),
                Irq: long.Parse(p[6]),
                Softirq: long.Parse(p[7]),
                Steal: p.Length > 8 ? long.Parse(p[8]) : 0L
            ));
        }

        return result;
    }

    private static async Task<string> ReadCpuModelNameAsync()
    {
        var lines = await File.ReadAllLinesAsync("/proc/cpuinfo");
        var line = lines.FirstOrDefault(l => l.StartsWith("model name", StringComparison.OrdinalIgnoreCase));
        return line is not null ? line.Split(':')[1].Trim() : "Unknown";
    }

    private static CpuSnapshot ComputeCpuUsage(string modelName, List<RawCpuLine> s1, List<RawCpuLine> s2)
    {
        // Index 0 = aggregate "cpu" row; indices 1+ = "cpu0", "cpu1"
        var totalUsage = s1.Count > 0 ? Usage(s1[0], s2[0]) : 0.0;
        var coreUsages = s1.Skip(1).Zip(s2.Skip(1), Usage).ToList();

        return new CpuSnapshot(modelName, totalUsage, coreUsages);

        static double Usage(RawCpuLine a, RawCpuLine b)
        {
            var idleDelta = (b.Idle + b.Iowait) - (a.Idle + a.Iowait);
            var totalDelta = (b.User + b.Nice + b.System + b.Idle + b.Iowait + b.Irq + b.Softirq + b.Steal)
                             - (a.User + a.Nice + a.System + a.Idle + a.Iowait + a.Irq + a.Softirq + a.Steal);
            return totalDelta <= 0 ? 0.0 : Math.Round((1.0 - (double)idleDelta / totalDelta) * 100.0, 2);
        }
    }

}