using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Polly;
using System;
using System.Data.SqlClient;

namespace Microsoft.AspNetCore.Hosting
{
    public static class IWebHostExtensions
    {
        public static bool IsInKubernetes(this IServiceProvider services)
        {
            var cfg = services.GetService<IConfiguration>();
            var orchestratorType = cfg.GetValue<string>("OrchestratorType");
            return orchestratorType?.ToUpper() == "K8S";
        }

        public static IServiceProvider MigrateDbContext<TContext>(this IServiceProvider services, Action<TContext, IServiceProvider> seeder) where TContext : DbContext
        {
            var underK8s = services.IsInKubernetes();

            using var scope = services.CreateScope();
            var scopeServices = scope.ServiceProvider;
            var logger = scopeServices.GetRequiredService<ILogger<TContext>>();
            var context = scopeServices.GetService<TContext>();

            try
            {
                logger.LogInformation("Migrating database associated with context {DbContextName}", typeof(TContext).Name);

                if (underK8s)
                {
                    InvokeSeeder(seeder, context, scopeServices);
                }
                else
                {
                    var retries = 10;
                    var retry = Policy.Handle<SqlException>()
                        .WaitAndRetry(
                            retryCount: retries,
                            sleepDurationProvider: retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)),
                            onRetry: (exception, timeSpan, retry, ctx) =>
                            {
                                logger.LogWarning(exception, "[{prefix}] Error migrating database (attempt {retry} of {retries})", nameof(TContext), retry, retries);
                            });

                    //if the sql server container is not created on run docker compose this
                    //migration can't fail for network related exception. The retry options for DbContext only 
                    //apply to transient exceptions
                    // Note that this is NOT applied when running some orchestrators (let the orchestrator to recreate the failing service)
                    retry.Execute(() => InvokeSeeder(seeder, context, scopeServices));
                }

                logger.LogInformation("Migrated database associated with context {DbContextName}", typeof(TContext).Name);
            }
            catch (Exception ex)
            {
                logger.LogError(ex, "An error occurred while migrating the database used on context {DbContextName}", typeof(TContext).Name);
                if (underK8s)
                {
                    throw;          // Rethrow under k8s because we rely on k8s to re-run the pod
                }
            }

            return services;
        }

        private static void InvokeSeeder<TContext>(Action<TContext, IServiceProvider> seeder, TContext context, IServiceProvider services)
            where TContext : DbContext
        {
            context.Database.Migrate();
            seeder(context, services);
        }
    }
}
