// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Diagnostics.CodeAnalysis;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.FileProviders;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace Microsoft.AspNetCore.StaticFiles
{
    /// <summary>
    /// Enables serving static files for a given request path
    /// </summary>
    public class StaticFileMiddleware
    {
        private readonly StaticFileOptions _options;
        private readonly PathString _matchUrl;
        private readonly RequestDelegate _next;
        private readonly ILogger _logger;
        private readonly IFileProvider _fileProvider;
        private readonly IContentTypeProvider _contentTypeProvider;

        /// <summary>
        /// Creates a new instance of the StaticFileMiddleware.
        /// </summary>
        /// <param name="next">The next middleware in the pipeline.</param>
        /// <param name="hostingEnv">The <see cref="IWebHostEnvironment"/> used by this middleware.</param>
        /// <param name="options">The configuration options.</param>
        /// <param name="loggerFactory">An <see cref="ILoggerFactory"/> instance used to create loggers.</param>
        public StaticFileMiddleware(RequestDelegate next, IWebHostEnvironment hostingEnv, IOptions<StaticFileOptions> options, ILoggerFactory loggerFactory)
        {
            if (next == null)
            {
                throw new ArgumentNullException(nameof(next));
            }

            if (hostingEnv == null)
            {
                throw new ArgumentNullException(nameof(hostingEnv));
            }

            if (options == null)
            {
                throw new ArgumentNullException(nameof(options));
            }

            if (loggerFactory == null)
            {
                throw new ArgumentNullException(nameof(loggerFactory));
            }

            _next = next;
            _options = options.Value;
            _contentTypeProvider = _options.ContentTypeProvider ?? new FileExtensionContentTypeProvider();
            _fileProvider = _options.FileProvider ?? Helpers.ResolveFileProvider(hostingEnv);
            _matchUrl = _options.RequestPath;
            _logger = loggerFactory.CreateLogger<StaticFileMiddleware>();
        }

        /// <summary>
        /// Processes a request to determine if it matches a known file, and if so, serves it.
        /// </summary>
        /// <param name="context"></param>
        /// <returns></returns>
        public Task Invoke(HttpContext context)
        {
            if (!ValidateNoEndpoint(context))
            {
                _logger.EndpointMatched();
            }
            else if (!ValidateMethod(context))
            {
                _logger.RequestMethodNotSupported(context.Request.Method);
            }
            else if (!ValidatePath(context, _matchUrl, out var subPath))
            {
                _logger.PathMismatch(subPath);
            }
            else if (!LookupContentType(_contentTypeProvider, _options, subPath, out var contentType))
            {
                _logger.FileTypeNotSupported(subPath);
            }
            else
            {
                // If we get here, we can try to serve the file
                return TryServeStaticFile(context, contentType, subPath);
            }

            return _next(context);
        }

        // Return true because we only want to run if there is no endpoint.
        private static bool ValidateNoEndpoint(HttpContext context) => context.GetEndpoint() == null;

        private static bool ValidateMethod(HttpContext context)
        {
            return Helpers.IsGetOrHeadMethod(context.Request.Method);
        }

        internal static bool ValidatePath(HttpContext context, PathString matchUrl, out PathString subPath) => Helpers.TryMatchPath(context, matchUrl, forDirectory: false, out subPath);

        internal static bool LookupContentType(IContentTypeProvider contentTypeProvider, StaticFileOptions options, PathString subPath, out string? contentType)
        {
            if (contentTypeProvider.TryGetContentType(subPath.Value!, out contentType))
            {
                return true;
            }

            if (options.ServeUnknownFileTypes)
            {
                contentType = options.DefaultContentType;
                return true;
            }

            return false;
        }

        private Task TryServeStaticFile(HttpContext context, string? contentType, PathString subPath)
        {
            var fileContext = new StaticFileContext(context, _options, _logger, _fileProvider, contentType, subPath);

            if (!fileContext.LookupFileInfo())
            {
                _logger.FileNotFound(fileContext.SubPath);
            }
            else
            {
                // If we get here, we can try to serve the file
                return fileContext.ServeStaticFile(context, _next);
            }

            return _next(context);
        }
    }
}
