namespace TodoList.Application.Common.Exceptions;

public class ValidationException : Exception
{
    public ValidationException() : base("One or more validation failures have occurred.")
    {
    }

    public ValidationException(string failures)
        : base(failures)
    {
    }
}

using FluentValidation;
using FluentValidation.Results;
using MediatR;
using ValidationException = TodoList.Application.Common.Exceptions.ValidationException;

namespace TodoList.Application.Common.Behaviors;

public class ValidationBehaviour<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    where TRequest : notnull
{
    private readonly IEnumerable<IValidator<TRequest>> _validators;

    // 注入所有自定義的Validators
    public ValidationBehaviour(IEnumerable<IValidator<TRequest>> validators) 
        => _validators = validators;

    public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next)
    {
        if (_validators.Any())
        {
            var context = new ValidationContext<TRequest>(request);

            var validationResults = await Task.WhenAll(_validators.Select(v => v.ValidateAsync(context, cancellationToken)));

            var failures = validationResults
                .Where(r => r.Errors.Any())
                .SelectMany(r => r.Errors)
                .ToList();

            // 如果有validator校驗失敗，拋出異常，這里的異常是我們自定義的包裝類型
            if (failures.Any())
                throw new ValidationException(GetValidationErrorMessage(failures));
        }
        return await next();
    }

    // 格式化校驗失敗消息
    private string GetValidationErrorMessage(IEnumerable<ValidationFailure> failures)
    {
        var failureDict = failures
            .GroupBy(e => e.PropertyName, e => e.ErrorMessage)
            .ToDictionary(failureGroup => failureGroup.Key, failureGroup => failureGroup.ToArray());

        return string.Join(";", failureDict.Select(kv => kv.Key + ": " + string.Join(' ', kv.Value.ToArray())));
    }
}

// 省略其他...
services.AddValidatorsFromAssembly(Assembly.GetExecutingAssembly());
services.AddTransient(typeof(IPipelineBehavior<,>), typeof(ValidationBehaviour<,>) 

using FluentValidation;
using Microsoft.EntityFrameworkCore;
using TodoList.Application.Common.Interfaces;
using TodoList.Domain.Entities;

namespace TodoList.Application.TodoItems.Commands.CreateTodoItem;

public class CreateTodoItemCommandValidator : AbstractValidator<CreateTodoItemCommand>
{
    private readonly IRepository<TodoItem> _repository;

    public CreateTodoItemCommandValidator(IRepository<TodoItem> repository)
    {
        _repository = repository;

        // 我們把最大長度限制到10，以便更好地驗證這個校驗
        // 更多的用法請參考FluentValidation官方文檔
        RuleFor(v => v.Title)
            .MaximumLength(10).WithMessage("TodoItem title must not exceed 10 characters.").WithSeverity(Severity.Warning)
            .NotEmpty().WithMessage("Title is required.").WithSeverity(Severity.Error)
            .MustAsync(BeUniqueTitle).WithMessage("The specified title already exists.").WithSeverity(Severity.Warning);
    }

    public async Task<bool> BeUniqueTitle(string title, CancellationToken cancellationToken)
    {
        return await _repository.GetAsQueryable().AllAsync(l => l.Title != title, cancellationToken);
    }
}

// 省略其他...
var response = await next();
//Response
_logger.LogInformation($"Handled {typeof(TResponse).Name}");

return response;

using System.Reflection;
using MediatR.Pipeline;
using Microsoft.Extensions.Logging;

public class LoggingBehaviour<TRequest> : IRequestPreProcessor<TRequest> where TRequest : notnull
{
    private readonly ILogger<LoggingBehaviour<TRequest>> _logger;

    // 在構造函數中后面我們還可以注入類似ICurrentUser和IIdentity相關的對象進行日志輸出
    public LoggingBehaviour(ILogger<LoggingBehaviour<TRequest>> logger)
    {
        _logger = logger;
    }

    public async Task Process(TRequest request, CancellationToken cancellationToken)
    {
        // 你可以在這里log關于請求的任何信息
        _logger.LogInformation($"Handling {typeof(TRequest).Name}");

        IList<PropertyInfo> props = new List<PropertyInfo>(request.GetType().GetProperties());
        foreach (var prop in props)
        {
            var propValue = prop.GetValue(request, null);
            _logger.LogInformation("{Property} : {@Value}", prop.Name, propValue);
        }
    }
}

// 省略其他...
services.AddTransient(typeof(IPipelineBehavior<,>), typeof(LoggingBehaviour<,>));