namespace MoonlightServers.Daemon.Helpers;

public partial class SystemMetrics
{
    /// <summary>Memory figures derived from <c>/proc/meminfo</c>.</summary>
    /// <param name="TotalBytes">Physical RAM installed.</param>
    /// <param name="UsedBytes">RAM actively in use (<c>Total - Available</c>).</param>
    /// <param name="FreeBytes">Completely unallocated RAM.</param>
    /// <param name="CachedBytes">Page cache + reclaimable slab — matches the <c>cached</c> column in <c>free -h</c>.</param>
    /// <param name="BuffersBytes">Kernel I/O buffer memory.</param>
    /// <param name="AvailableBytes">Estimated RAM available for new allocations without swapping.</param>
    /// <param name="UsedPercent">UsedBytes / TotalBytes as a percentage (0–100).</param>
    public record MemoryInfo(
        long TotalBytes,
        long UsedBytes,
        long FreeBytes,
        long CachedBytes,
        long BuffersBytes,
        long AvailableBytes,
        double UsedPercent
    );
    
    // Memory  —  /proc/meminfo

    /// <summary>
    /// Parses <c>/proc/meminfo</c> into a <see cref="MemoryInfo"/> record.
    /// The <c>CachedBytes</c> field is computed as
    /// <c>Cached + SReclaimable - Shmem</c> to match the value shown by <c>free -h</c>.
    /// </summary>
    private static async Task<MemoryInfo> ReadMemoryAsync()
    {
        var lines = await File.ReadAllLinesAsync("/proc/meminfo");
        var map = new Dictionary<string, long>(StringComparer.Ordinal);

        foreach (var line in lines)
        {
            var colon = line.IndexOf(':');
            if (colon < 0)
                continue;

            var key = line[..colon].Trim();
            var val = line[(colon + 1)..].Trim().Split(' ')[0]; // Strip "kB" suffix.
            if (long.TryParse(val, out var kb))
                map[key] = kb * 1024L;
        }

        var total = map.GetValueOrDefault("MemTotal");
        var available = map.GetValueOrDefault("MemAvailable");
        var free = map.GetValueOrDefault("MemFree");
        var buffers = map.GetValueOrDefault("Buffers");
        var cached = map.GetValueOrDefault("Cached")
                     + map.GetValueOrDefault("SReclaimable")
                     - map.GetValueOrDefault("Shmem");
        var used = total - available;
        var usedPct = total > 0 ? Math.Round((double)used / total * 100.0, 2) : 0.0;

        return new MemoryInfo(total, used, free, cached, buffers, available, usedPct);
    }
}