source: TFP-WebServer/WebServer/src/WebAPI/OpenApiHelpers.cs@ 459

using System.Collections.Generic;
using System.IO;
using System.Reflection;
using System.Text;

namespace Webserver.WebAPI {
        public class OpenApiHelpers {
                private const string masterResourceName = "openapi.master.yaml";
                private const string masterDocName = "openapi.yaml";

                private const string masterDocRefLineBegin = "    - $ref: ";
                private const string masterDocRefLineEnd = "#/paths";

                private readonly Dictionary<string, string> specs = new CaseInsensitiveStringDictionary<string> ();

                public OpenApiHelpers () {
                        loadMainSpec ();
                        Web.ServerInitialized += _ => {
                                buildMainSpecRefs ();
                        };
                }

                private void loadMainSpec () {
                        Assembly apiAssembly = GetType ().Assembly;

                        string specText = ResourceHelpers.GetManifestResourceText (apiAssembly, masterResourceName, true);
                        if (specText == null) {
                                Log.Warning ($"[Web] Failed loading main OpenAPI spec from assembly '{Path.GetFileName (apiAssembly.Location)}'");
                                return;
                        }

                        specs.Add (masterDocName, specText);
                        Log.Out ($"[Web] Loaded main OpenAPI spec");
                }

                private void buildMainSpecRefs () {
                        if (!TryGetOpenApiSpec (null, out string mainSpec)) {
                                return;
                        }

                        StringBuilder sb = new StringBuilder (mainSpec);
                        
                        foreach ((string apiSpecName, _) in specs) {
                                if (apiSpecName.Equals (masterDocName)) {
                                        continue;
                                }

                                sb.AppendLine ($"{masterDocRefLineBegin}./{apiSpecName}{masterDocRefLineEnd}");
                        }

                        specs[masterDocName] = sb.ToString ();
                        
                        Log.Out ("[Web] OpenAPI preparation done");
                }

                public void LoadOpenApiSpec (AbsWebAPI _api) {
                        Assembly apiAssembly = _api.GetType ().Assembly;
                        string apiName = _api.Name;
                        string apiSpecName = $"{apiName}.openapi.yaml";

                        string specText = ResourceHelpers.GetManifestResourceText (apiAssembly, apiSpecName, true);
                        if (specText == null) {
                                return;
                        }

                        Log.Out ($"[Web] Loaded OpenAPI spec for '{apiName}'");
                        specs.Add (apiSpecName, specText);
                }

                public bool TryGetOpenApiSpec (string _name, out string _specText) {
                        if (string.IsNullOrEmpty (_name)) {
                                _name = masterDocName;
                        }

                        return specs.TryGetValue (_name, out _specText);
                }
        }
}