// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Metadata;
using Microsoft.Extensions.Options;
 
namespace Microsoft.AspNetCore.Diagnostics;
 
/// <summary>
/// A middleware for generating the response body of error status codes with no body.
/// </summary>
public class StatusCodePagesMiddleware
{
    private readonly RequestDelegate _next;
    private readonly StatusCodePagesOptions _options;
 
    /// <summary>
    /// Creates a new <see cref="StatusCodePagesMiddleware"/>
    /// </summary>
    /// <param name="next">The <see cref="RequestDelegate"/> representing the next middleware in the pipeline.</param>
    /// <param name="options">The options for configuring the middleware.</param>
    public StatusCodePagesMiddleware(RequestDelegate next, IOptions<StatusCodePagesOptions> options)
    {
        _next = next;
        _options = options.Value;
        if (_options.HandleAsync == null)
        {
            throw new ArgumentException("Missing options.HandleAsync implementation.");
        }
    }
 
    /// <summary>
    /// Executes the middleware.
    /// </summary>
    /// <param name="context">The <see cref="HttpContext"/> for the current request.</param>
    /// <returns>A task that represents the execution of this middleware.</returns>
    public async Task Invoke(HttpContext context)
    {
        var statusCodeFeature = new StatusCodePagesFeature();
        context.Features.Set<IStatusCodePagesFeature>(statusCodeFeature);
        var endpoint = context.GetEndpoint();
        var shouldCheckEndpointAgain = endpoint is null;
 
        if (HasSkipStatusCodePagesMetadata(endpoint))
        {
            statusCodeFeature.Enabled = false;
        }
 
        await _next(context);
 
        if (!statusCodeFeature.Enabled)
        {
            // Check if the feature is still available because other middleware (such as a web API written in MVC) could
            // have disabled the feature to prevent HTML status code responses from showing up to an API client.
            return;
        }
 
        if (shouldCheckEndpointAgain && HasSkipStatusCodePagesMetadata(context.GetEndpoint()))
        {
            // If the endpoint was null check the endpoint again since it could have been set by another middleware.
            return;
        }
 
        // Do nothing if a response body has already been provided.
        if (context.Response.HasStarted
            || context.Response.StatusCode < 400
            || context.Response.StatusCode >= 600
            || context.Response.ContentLength.HasValue
            || !string.IsNullOrEmpty(context.Response.ContentType))
        {
            return;
        }
 
        var statusCodeContext = new StatusCodeContext(context, _options, _next);
        await _options.HandleAsync(statusCodeContext);
    }
 
    private static bool HasSkipStatusCodePagesMetadata(Endpoint? endpoint)
    {
        var skipStatusCodePageMetadata = endpoint?.Metadata.GetMetadata<ISkipStatusCodePagesMetadata>();
 
        return skipStatusCodePageMetadata is not null;
    }
}