const std = @import("std");

pub const WindowsVersion = std.Target.Os.WindowsVersion;

/// Returns the highest known WindowsVersion deduced from reported runtime information.
/// Discards information about in-between versions we don't differentiate.
pub fn detectRuntimeVersion() WindowsVersion {
    var version_info: std.os.windows.RTL_OSVERSIONINFOW = undefined;
    version_info.dwOSVersionInfoSize = @sizeOf(@TypeOf(version_info));

    switch (std.os.windows.ntdll.RtlGetVersion(&version_info)) {
        .SUCCESS => {},
        else => unreachable,
    }

    // Starting from the system infos build a NTDDI-like version
    // constant whose format is:
    //   B0 B1 B2 B3
    //   `---` `` ``--> Sub-version (Starting from Windows 10 onwards)
    //     \    `--> Service pack (Always zero in the constants defined)
    //      `--> OS version (Major & minor)
    const os_ver: u16 = @intCast(u16, version_info.dwMajorVersion & 0xff) << 8 |
        @intCast(u16, version_info.dwMinorVersion & 0xff);
    const sp_ver: u8 = 0;
    const sub_ver: u8 = if (os_ver >= 0x0A00) subver: {
        // There's no other way to obtain this info beside
        // checking the build number against a known set of
        // values
        var last_idx: usize = 0;
        for (WindowsVersion.known_win10_build_numbers) |build, i| {
            if (version_info.dwBuildNumber >= build)
                last_idx = i;
        }
        break :subver @truncate(u8, last_idx);
    } else 0;

    const version: u32 = @as(u32, os_ver) << 16 | @as(u16, sp_ver) << 8 | sub_ver;

    return @intToEnum(WindowsVersion, version);
}