// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Linq;
using System.Threading.Tasks;
using JetBrains.Annotations;
using Microsoft.AspNet.Builder;
using Microsoft.AspNet.Diagnostics.Entity.Utilities;
using Microsoft.AspNet.Diagnostics.Entity.Views;
using Microsoft.AspNet.Http;
using Microsoft.Data.Entity;
using Microsoft.Data.Entity.Infrastructure;
using Microsoft.Data.Entity.Migrations;
using Microsoft.Data.Entity.Storage;
using Microsoft.Extensions.Logging;

namespace Microsoft.AspNet.Diagnostics.Entity
{
    public class DatabaseErrorPageMiddleware
    {
        private readonly RequestDelegate _next;
        private readonly DatabaseErrorPageOptions _options;
        private readonly IServiceProvider _serviceProvider;
        private readonly ILogger _logger;
        private readonly DataStoreErrorLoggerProvider _loggerProvider;

        public DatabaseErrorPageMiddleware([NotNull] RequestDelegate next, [NotNull] IServiceProvider serviceProvider, [NotNull] ILoggerFactory loggerFactory, [NotNull] DatabaseErrorPageOptions options)
        {
            Check.NotNull(next, nameof(next));
            Check.NotNull(serviceProvider, nameof(serviceProvider));
            Check.NotNull(loggerFactory, nameof(loggerFactory));
            Check.NotNull(options, nameof(options));

            _next = next;
            _serviceProvider = serviceProvider;
            _options = options;
            _logger = loggerFactory.CreateLogger<DatabaseErrorPageMiddleware>();

            _loggerProvider = new DataStoreErrorLoggerProvider();
            loggerFactory.AddProvider(_loggerProvider);
        }

        public virtual async Task Invoke([NotNull] HttpContext context)
        {
            Check.NotNull(context, "context");

            try
            {
#if !DNXCORE50
                // TODO This probably isn't the correct place for this workaround, it
                //      needs to be called before anything is written to CallContext
                // http://msdn.microsoft.com/en-us/library/dn458353(v=vs.110).aspx
                System.Configuration.ConfigurationManager.GetSection("system.xml/xmlReader");
#endif
                _loggerProvider.Logger.StartLoggingForCurrentCallContext();

                await _next(context);
            }
            catch (Exception ex)
            {
                try
                {
                    if (ShouldDisplayErrorPage(_loggerProvider.Logger.LastError, ex, _logger))
                    {
                        var dbContextType = _loggerProvider.Logger.LastError.ContextType;
                        var dbContext = (DbContext)context.RequestServices.GetService(dbContextType);
                        if (dbContext == null)
                        {
                            _logger.LogError(Strings.FormatDatabaseErrorPageMiddleware_ContextNotRegistered(dbContextType.FullName));
                        }
                        else
                        {
                            var creator = dbContext.GetService<IDatabaseCreator>() as IRelationalDatabaseCreator;
                            if (creator == null)
                            {
                                _logger.LogVerbose(Strings.DatabaseErrorPage_NotRelationalDatabase);
                            }
                            else
                            {
                                var databaseExists = creator.Exists();

                                var historyRepository = dbContext.GetService<IHistoryRepository>();
                                var migrationsAssembly = dbContext.GetService<IMigrationsAssembly>();
                                var modelDiffer = dbContext.GetService<IMigrationsModelDiffer>();

                                var appliedMigrations = historyRepository.GetAppliedMigrations();
                                var pendingMigrations = (
                                        from m in migrationsAssembly.Migrations
                                        where !appliedMigrations.Any(
                                            r => string.Equals(r.MigrationId, m.Key, StringComparison.OrdinalIgnoreCase))
                                        select m.Key)
                                    .ToList();

                                // HasDifferences will return true if there is no model snapshot, but if there is an existing database
                                // and no model snapshot then we don't want to show the error page since they are most likely targeting
                                // and existing database and have just misconfigured their model
                                var pendingModelChanges = migrationsAssembly.ModelSnapshot == null && databaseExists
                                    ? false
                                    : modelDiffer.HasDifferences(migrationsAssembly.ModelSnapshot?.Model, dbContext.Model);

                                if ((!databaseExists && pendingMigrations.Any()) || pendingMigrations.Any() || pendingModelChanges)
                                {
                                    var page = new DatabaseErrorPage();
                                    page.Model = new DatabaseErrorPageModel(dbContextType, ex, databaseExists, pendingModelChanges, pendingMigrations, _options);
                                    await page.ExecuteAsync(context);
                                    return;
                                }
                            }
                        }
                    }
                }
                catch (Exception e)
                {
                    _logger.LogError(Strings.DatabaseErrorPageMiddleware_Exception, e);
                }

                throw;
            }
        }

        private static bool ShouldDisplayErrorPage(DataStoreErrorLogger.DataStoreErrorLog lastError, Exception exception, ILogger logger)
        {
            logger.LogVerbose(Strings.FormatDatabaseErrorPage_AttemptingToMatchException(exception.GetType()));

            if (!lastError.IsErrorLogged)
            {
                logger.LogVerbose(Strings.DatabaseErrorPage_NoRecordedException);
                return false;
            }

            bool match = false;
            for (var e = exception; e != null && !match; e = e.InnerException)
            {
                match = lastError.Exception == e;
            }

            if (!match)
            {
                logger.LogVerbose(Strings.DatabaseErrorPage_NoMatch);
                return false;
            }

            logger.LogVerbose(Strings.DatabaseErrorPage_Matched);
            return true;
        }
    }
}