using System.Runtime.InteropServices;
using Monitor.Protocol;

namespace Monitor.Measurement;

/// <summary>
/// 读出本机的系统名和架构，只用于在面板上展示。故意只取粗粒度的信息：
/// 「Debian 12」「Windows 11」「x64」，不读主机名、内核版本、CPU 型号。
/// </summary>
public static class PlatformDetector
{
    public static PlatformInfo Detect()
    {
        PlatformInfo info = Detect(File.Exists("/etc/os-release") ? File.ReadAllLines("/etc/os-release") : []);
        info.Version = Empty(BuildInfo.Version);
        info.Tag = Empty(BuildInfo.Tag);
        info.Commit = Empty(BuildInfo.Commit);
        info.BuiltAt = Empty(BuildInfo.BuiltAt);
        return info;
    }

    private static string? Empty(string value) => value.Length == 0 ? null : value;

    /// <summary>`osRelease` 是 /etc/os-release 的各行（Linux 之外不用）。拆出来是为了好测。</summary>
    internal static PlatformInfo Detect(IEnumerable<string> osRelease)
    {
        string arch = RuntimeInformation.OSArchitecture switch
        {
            Architecture.X64 => "x64",
            Architecture.Arm64 => "arm64",
            Architecture.Arm => "arm",
            Architecture.X86 => "x86",
            var other => other.ToString().ToLowerInvariant(),
        };

        if (OperatingSystem.IsWindows())
        {
            // Windows 11 的版本号还是 10.0，靠内部版本号（22000 起）区分
            string name = Environment.OSVersion.Version.Build >= 22000 ? "Windows 11" : "Windows 10";
            return new PlatformInfo { Os = "windows", Name = name, Arch = arch };
        }

        if (OperatingSystem.IsMacOS())
        {
            return new PlatformInfo { Os = "macos", Name = "macOS", Arch = arch };
        }

        if (OperatingSystem.IsLinux())
        {
            return new PlatformInfo { Os = "linux", Name = LinuxName(osRelease), Arch = arch };
        }

        return new PlatformInfo { Os = "other", Name = null, Arch = arch };
    }

    /// <summary>从 os-release 里取发行版名字和主版本：「Debian GNU/Linux 12 (bookworm)」→「Debian 12」，「OpenWrt 24.10.0」→「OpenWrt 24.10」。</summary>
    internal static string LinuxName(IEnumerable<string> osRelease)
    {
        var values = new Dictionary<string, string>(StringComparer.Ordinal);
        foreach (string line in osRelease)
        {
            int eq = line.IndexOf('=', StringComparison.Ordinal);
            if (eq > 0)
            {
                values[line[..eq].Trim()] = line[(eq + 1)..].Trim().Trim('"', '\'');
            }
        }

        string name = values.GetValueOrDefault("NAME") ?? values.GetValueOrDefault("ID") ?? "Linux";
        name = name.Replace(" GNU/Linux", string.Empty, StringComparison.Ordinal).Trim();
        string? version = values.GetValueOrDefault("VERSION_ID");
        if (string.IsNullOrEmpty(version))
        {
            return name;
        }

        // 只留 主.次：Alpine 的 3.22.1、OpenWrt 的 24.10.0 都截成两段；Debian 的 12 本来就一段
        string[] parts = version.Split('.');
        return $"{name} {string.Join('.', parts.Take(2))}";
    }
}