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HTML / CSS / JS

// Global exception handling in ASP.NET Core (.NET 8 minimal API)

using Microsoft.AspNetCore.Diagnostics;
using Microsoft.AspNetCore.Mvc;

var builder = WebApplication.CreateBuilder(args);

// Register custom exception handler (IExceptionHandler, .NET 8+)
builder.Services.AddExceptionHandler<GlobalExceptionHandler>();
builder.Services.AddProblemDetails();

var app = builder.Build();

// Enable exception handler middleware
app.UseExceptionHandler();

// Minimal API endpoints
app.MapGet("/divide/{a}/{b}", (int a, int b) =>
{
    if (b == 0) throw new DivideByZeroException("Cannot divide by zero.");
    return Results.Ok(new { Result = a / b });
});

app.MapGet("/validate/{age}", (int age) =>
{
    if (age < 0) throw new ValidationException("age", age, "Age must be non-negative.");
    return Results.Ok(new { Age = age });
});

app.Run();

// ---- IExceptionHandler implementation ----
public sealed class GlobalExceptionHandler : IExceptionHandler
{
    private readonly ILogger<GlobalExceptionHandler> _logger;
    public GlobalExceptionHandler(ILogger<GlobalExceptionHandler> logger)
        => _logger = logger;

public async ValueTask<bool> TryHandleAsync(
        HttpContext ctx,
        Exception   exception,
        CancellationToken ct)
    {
        _logger.LogError(exception, "Unhandled exception: {Message}", exception.Message);

var (status, title) = exception switch
        {
            ValidationException   => (400, "Validation Error"),
            DivideByZeroException => (400, "Bad Request"),
            _                     => (500, "Internal Server Error")
        };

var problem = new ProblemDetails
        {
            Status = status,
            Title  = title,
            Detail = exception.Message
        };

ctx.Response.StatusCode = status;
        await ctx.Response.WriteAsJsonAsync(problem, ct);
        return true; // handled
    }
}