using System;

using System.Linq;

using System.Collections.Generic;

public class Program {

    public static void Main() {

        var serviceCall = SomeServiceMethod();

        if (!serviceCall.IsSuccessful)

        {

            Console.WriteLine(serviceCall.GetRootError().Message);

            return;

        }

        Console.WriteLine(serviceCall.Data);

    }

    public static Result<string> SomeServiceMethod() {

        //some task;

        var random = new Random();

        if (random.NextDouble() > 0.5F) {

            return Result.Fail<string>("Oh no it failed", "general-failure");

        }

        return "Great it worked!";

    }

}

public class EmptyResponse

{

​

    public EmptyResponse()

    {

        Items = Array.Empty<string>();

    }

    public string[] Items { get; set; }

}

​

public record Error

{

    public string? Message { get; init; }

    public string? ErrorType { get; init; }

    public List<Error> Reasons { get; init; } = new List<Error>();

​

    public Error() { }

    public Error(string message) => Message = message;

    public static Error FromError(Error error)

    {

        List<Error> reasonsList = error.Reasons.Select(FromError).ToList();

        return new Error

        {

            Message = error.Message,

            Reasons = reasonsList,

            ErrorType = error.ErrorType

        };

    }

}

​

public abstract record Result

{

    public static Result<EmptyResponse> Ok()

        => new() { Data = new EmptyResponse() };

    public static Result<TData> Ok<TData>(TData data)

        => new() { Data = data };

    public static Result<EmptyResponse> Fail(string errorMessage, string? errorType = null)

        =>  Fail<EmptyResponse>(errorMessage, errorType);

    public static Result<EmptyResponse> Fail(Error error)

        =>  Fail<EmptyResponse>(error);

​

    public static Result<TReturnType> Fail<TReturnType>(string errorMessage, string? errorType = null)

    {

        var error =  new Error(errorMessage);

        if (!string.IsNullOrEmpty(errorType))

            error = error with { ErrorType = errorType };

        return new Result<TReturnType>

        {

            Errors = new List<Error>() { error }

        };

    }

    public static Result<TReturnType> Fail<TReturnType>(Error error) =>

        new()

        {

            Errors = new List<Error>() { error }

        };

​

}

​

public record Result<TData>

{

    public bool IsSuccessful => !Errors.Any();

    public List<Error> Errors { get; init; } = new();

    public TData Data { get; init; }

    public Error? GetRootError() => Errors.FirstOrDefault();

    public static implicit operator TData?(Result<TData> result)

    {

        if (!result.IsSuccessful)

            throw new NullReferenceException("Unable to read data from a failed result");

        return result.Data;

    }

​

    public static implicit operator Result<TData>(TData data)

        => new() { Data = data };

}