GUID

pub const GUID = extern struct {
    Data1: u32,
    Data2: u16,
    Data3: u16,
    Data4: [8]u8,

    const hex_offsets: [16]u6 = .{
        6,  4,  2,  0,
        11, 9,  16, 14,
        19, 21, 24, 26,
        28, 30, 32, 34,
    };

    pub fn parse(s: []const u8) GUID {
        assert(s[0] == '{');
        assert(s[37] == '}');
        return parseNoBraces(s[1 .. s.len - 1]) catch @panic("invalid GUID string");
    }

    pub fn parseNoBraces(s: []const u8) !GUID {
        assert(s.len == 36);
        assert(s[8] == '-');
        assert(s[13] == '-');
        assert(s[18] == '-');
        assert(s[23] == '-');
        var raw1: [4]u8 = undefined;
        var raw2: [2]u8 = undefined;
        var raw3: [2]u8 = undefined;
        var raw4: [8]u8 = undefined;
        assert((try std.fmt.hexToBytes(&raw1, s[0..8])).len == raw1.len);
        assert((try std.fmt.hexToBytes(&raw2, s[9..13])).len == raw2.len);
        assert((try std.fmt.hexToBytes(&raw3, s[14..18])).len == raw3.len);
        assert((try std.fmt.hexToBytes(raw4[0..2], s[19..23])).len == 2);
        assert((try std.fmt.hexToBytes(raw4[2..8], s[24..36])).len == 6);
        return .{
            .Data1 = @byteSwap(@as(u32, @bitCast(raw1))),
            .Data2 = @byteSwap(@as(u16, @bitCast(raw2))),
            .Data3 = @byteSwap(@as(u16, @bitCast(raw3))),
            .Data4 = raw4,
        };
    }

    pub fn format(self: GUID, w: *std.Io.Writer) std.Io.Writer.Error!void {
        return w.print("{{{x:0>8}-{x:0>4}-{x:0>4}-{x}-{x}}}", .{
            self.Data1,
            self.Data2,
            self.Data3,
            self.Data4[0..2],
            self.Data4[2..8],
        });
    }

    test parse {
        const expected: GUID = .{
            .Data1 = 0x01234567,
            .Data2 = 0x89ab,
            .Data3 = 0xef10,
            .Data4 = "\x32\x54\x76\x98\xba\xdc\xfe\x91".*,
        };
        try std.testing.expectEqual(expected, GUID.parse("{01234567-89AB-EF10-3254-7698badcfe91}"));
    }

    test format {
        const guid0: GUID = .{ .Data1 = 1, .Data2 = 1, .Data3 = 1, .Data4 = .{ 0, 1, 0, 0, 0, 0, 0, 1 } };
        try std.testing.expectFmt("{00000001-0001-0001-0001-000000000001}", "{f}", .{guid0});

        const guid1: GUID = .parse("{01234567-89AB-EF10-3254-7698badcfe91}");
        try std.testing.expectFmt("{01234567-89ab-ef10-3254-7698badcfe91}", "{f}", .{guid1});
    }
}