using Microsoft.Azure.KeyVault;
using Microsoft.Azure.Services.AppAuthentication;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Configuration.AzureKeyVault;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection.Extensions;
using System;
using System.Linq;

[assembly: WebJobsStartup(typeof(Startup))]

namespace MyServices.Functions
{
    public class Startup : IWebJobsStartup
    {
        public static string Environment;

        public void Configure(IWebJobsBuilder builder)
        {
            var config = ReplaceConfiguration(builder);

            builder.Services.AddMyServices(config.GetSection("MySection"));
        }

        private static IConfiguration ReplaceConfiguration(IWebJobsBuilder builder)
        {
            var baseConfig = builder.Services.FirstOrDefault(d => d.ServiceType == typeof(IConfiguration))?.ImplementationInstance as IConfigurationRoot;
            Environment = baseConfig?.GetValue<string>("ASPNETCORE_ENVIRONMENT") ?? "Development";

            var config = new ConfigurationBuilder();
            if (baseConfig != null)
                config.AddConfiguration(baseConfig);

            config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                    .AddJsonFile($"appsettings.{Environment}.json", optional: true, reloadOnChange: true);

            if (Environment.Equals("Development", StringComparison.OrdinalIgnoreCase))
            {
                config.AddUserSecrets<Startup>();
            }
            config.AddEnvironmentVariables();

            if (!Environment.Equals("Development", StringComparison.OrdinalIgnoreCase))
            {
                var vaultConfig = config.Build().GetSection("ConfigurationVault");
                var url = vaultConfig.GetValue<string>("AzureVaultUrl");
                var tokenProvider = new AzureServiceTokenProvider();
                var kvClient = new KeyVaultClient((authority, resource, scope) => tokenProvider.KeyVaultTokenCallback(authority, resource, scope));
                config.AddAzureKeyVault(url, kvClient, new DefaultKeyVaultSecretManager());
            }

            var newConfig = config.Build();
            builder.Services.Replace(ServiceDescriptor.Singleton(typeof(IConfiguration), newConfig));
            return newConfig;
        }
    }
}