public static NuGetFramework ParseFolder()

in src/NuGet.Core/NuGet.Frameworks/NuGetFrameworkFactory.cs [254:375]
106 lines of code
25 McCabe index (conditional complexity)

        public static NuGetFramework ParseFolder(string folderName, IFrameworkNameProvider mappings)
        {
            if (folderName == null)
            {
                throw new ArgumentNullException(nameof(folderName));
            }

            if (mappings == null)
            {
                throw new ArgumentNullException(nameof(mappings));
            }

            if (folderName.IndexOf('%') > -1)
            {
                folderName = Uri.UnescapeDataString(folderName);
            }

            NuGetFramework? result;
            // first check if we have a special or common framework
            if (!TryParseSpecialFramework(folderName, out result)
                && !TryParseCommonFramework(folderName, out result))
            {
                // assume this is unsupported unless we find a match
                result = UnsupportedFramework;

                var parts = RawParse(folderName);

                if (parts != null)
                {
                    if (mappings.TryGetIdentifier(parts.Item1, out string? framework))
                    {
                        var version = FrameworkConstants.EmptyVersion;

                        if (parts.Item2 == null
                            || mappings.TryGetVersion(parts.Item2, out version))
                        {
                            string profileShort = parts.Item3;

                            if (version.Major >= 5
                                && (StringComparer.OrdinalIgnoreCase.Equals(FrameworkConstants.FrameworkIdentifiers.Net, framework)
                                    || StringComparer.OrdinalIgnoreCase.Equals(FrameworkConstants.FrameworkIdentifiers.NetCoreApp, framework)
                                   )
                                )
                            {
                                // net should be treated as netcoreapp in 5.0 and later
                                framework = FrameworkConstants.FrameworkIdentifiers.NetCoreApp;
                                if (!string.IsNullOrEmpty(profileShort))
                                {
                                    // Find a platform version if it exists and yank it out
                                    var platformChars = profileShort;
                                    var versionStart = 0;
                                    while (versionStart < platformChars.Length
                                           && IsLetterOrDot(platformChars[versionStart]))
                                    {
                                        versionStart++;
                                    }
                                    string platform = versionStart > 0 ? profileShort.Substring(0, versionStart) : profileShort;
                                    string? platformVersionString = versionStart > 0 ? profileShort.Substring(versionStart, profileShort.Length - versionStart) : null;

                                    // Parse the version if it's there.
                                    Version? platformVersion = FrameworkConstants.EmptyVersion;
                                    if ((string.IsNullOrEmpty(platformVersionString) || mappings.TryGetPlatformVersion(platformVersionString!, out platformVersion)))
                                    {
                                        result = new NuGetFramework(framework, version, platform ?? string.Empty, platformVersion ?? FrameworkConstants.EmptyVersion);
                                    }
                                    else
                                    {
                                        return result; // with result == UnsupportedFramework
                                    }
                                }
                                else
                                {
                                    result = new NuGetFramework(framework, version, string.Empty, FrameworkConstants.EmptyVersion);
                                }
                            }
                            else
                            {
                                if (!mappings.TryGetProfile(framework, profileShort, out string? profile))
                                {
                                    profile = profileShort ?? string.Empty;
                                }

                                if (StringComparer.OrdinalIgnoreCase.Equals(FrameworkConstants.FrameworkIdentifiers.Portable, framework))
                                {
                                    if (!mappings.TryGetPortableFrameworks(profileShort!, out IEnumerable<NuGetFramework>? clientFrameworks))
                                    {
                                        result = UnsupportedFramework;
                                    }
                                    else
                                    {
                                        var profileNumber = -1;
                                        if (mappings.TryGetPortableProfile(clientFrameworks, out profileNumber))
                                        {
                                            var portableProfileNumber = FrameworkNameHelpers.GetPortableProfileNumberString(profileNumber);
                                            result = new NuGetFramework(framework, version, portableProfileNumber);
                                        }
                                        else
                                        {
                                            result = new NuGetFramework(framework, version, profileShort);
                                        }
                                    }
                                }
                                else
                                {
                                    result = new NuGetFramework(framework, version, profile);
                                }
                            }
                        }
                    }
                }
                else
                {
                    // If the framework was not recognized check if it is a deprecated framework
                    if (TryParseDeprecatedFramework(folderName, out NuGetFramework? deprecated))
                    {
                        result = deprecated;
                    }
                }
            }

            return result;
        }