internal static string DeterminePrimaryScriptFile()

in src/WebJobs.Script/Host/HostFunctionMetadataProvider.cs [218:273]
42 lines of code
10 McCabe index (conditional complexity)

        internal static string DeterminePrimaryScriptFile(string scriptFile, string scriptDirectory, IFileSystem fileSystem = null)
        {
            fileSystem ??= FileUtility.Instance;

            // First see if there is an explicit primary file indicated
            // in config. If so use that.
            string functionPrimary = null;

            if (!string.IsNullOrEmpty(scriptFile))
            {
                string scriptPath = fileSystem.Path.Combine(scriptDirectory, scriptFile);
                if (!fileSystem.File.Exists(scriptPath))
                {
                    throw new FunctionConfigurationException("Invalid script file name configuration. The 'scriptFile' property is set to a file that does not exist.");
                }

                functionPrimary = scriptPath;
            }
            else
            {
                string[] functionFiles = fileSystem.Directory.EnumerateFiles(scriptDirectory)
                    .Where(p => fileSystem.Path.GetFileName(p).ToLowerInvariant() != ScriptConstants.FunctionMetadataFileName)
                    .ToArray();

                if (functionFiles.Length == 0)
                {
                    return null;
                }

                if (functionFiles.Length == 1)
                {
                    // if there is only a single file, that file is primary
                    functionPrimary = functionFiles[0];
                }
                else
                {
                    // if there is a "run" file, that file is primary,
                    // for Node, any index.js file is primary
                    // for Python, __init__.py file is primary
                    // TODO #6955: Get default function file name from language worker configs
                    functionPrimary = functionFiles.FirstOrDefault(p =>
                        fileSystem.Path.GetFileNameWithoutExtension(p).ToLowerInvariant() == "run" ||
                        fileSystem.Path.GetFileName(p).ToLowerInvariant() == "index.js" ||
                        fileSystem.Path.GetFileName(p).ToLowerInvariant() == "index.mjs" ||
                        fileSystem.Path.GetFileName(p).ToLowerInvariant() == "index.cjs" ||
                        fileSystem.Path.GetFileName(p).ToLowerInvariant() == "__init__.py");
                }
            }

            // Primary script file is not required for HttpWorker or any custom language worker
            if (string.IsNullOrEmpty(functionPrimary))
            {
                return null;
            }
            return Path.GetFullPath(functionPrimary);
        }