// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Diagnostics;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
 
namespace Microsoft.AspNetCore.Hosting;
 
// This exists solely to bootstrap the configuration
internal sealed class BootstrapHostBuilder : IHostBuilder
{
    private readonly HostApplicationBuilder _builder;
 
    private readonly List<Action<IConfigurationBuilder>> _configureHostActions = new();
    private readonly List<Action<HostBuilderContext, IConfigurationBuilder>> _configureAppActions = new();
    private readonly List<Action<HostBuilderContext, IServiceCollection>> _configureServicesActions = new();
 
    public BootstrapHostBuilder(HostApplicationBuilder builder)
    {
        _builder = builder;
 
        foreach (var descriptor in _builder.Services)
        {
            if (descriptor.ServiceType == typeof(HostBuilderContext))
            {
                Context = (HostBuilderContext)descriptor.ImplementationInstance!;
                break;
            }
        }
 
        if (Context is null)
        {
            throw new InvalidOperationException($"{nameof(HostBuilderContext)} must exist in the {nameof(IServiceCollection)}");
        }
    }
 
    public IDictionary<object, object> Properties => Context.Properties;
 
    public HostBuilderContext Context { get; }
 
    public IHostBuilder ConfigureHostConfiguration(Action<IConfigurationBuilder> configureDelegate)
    {
        _configureHostActions.Add(configureDelegate ?? throw new ArgumentNullException(nameof(configureDelegate)));
        return this;
    }
 
    public IHostBuilder ConfigureAppConfiguration(Action<HostBuilderContext, IConfigurationBuilder> configureDelegate)
    {
        _configureAppActions.Add(configureDelegate ?? throw new ArgumentNullException(nameof(configureDelegate)));
        return this;
    }
 
    public IHostBuilder ConfigureServices(Action<HostBuilderContext, IServiceCollection> configureDelegate)
    {
        _configureServicesActions.Add(configureDelegate ?? throw new ArgumentNullException(nameof(configureDelegate)));
        return this;
    }
 
    public IHost Build()
    {
        // ConfigureWebHostDefaults should never call this.
        throw new InvalidOperationException();
    }
 
    public IHostBuilder ConfigureContainer<TContainerBuilder>(Action<HostBuilderContext, TContainerBuilder> configureDelegate)
    {
        // ConfigureWebHostDefaults should never call this.
        throw new InvalidOperationException();
    }
 
    public IHostBuilder UseServiceProviderFactory<TContainerBuilder>(IServiceProviderFactory<TContainerBuilder> factory) where TContainerBuilder : notnull
    {
        // ConfigureWebHostDefaults should never call this.
        throw new InvalidOperationException();
    }
 
    public IHostBuilder UseServiceProviderFactory<TContainerBuilder>(Func<HostBuilderContext, IServiceProviderFactory<TContainerBuilder>> factory) where TContainerBuilder : notnull
    {
        // ConfigureWebHostDefaults should never call this.
        throw new InvalidOperationException();
    }
 
    public ServiceDescriptor RunDefaultCallbacks()
    {
        foreach (var configureHostAction in _configureHostActions)
        {
            configureHostAction(_builder.Configuration);
        }
 
        // ConfigureAppConfiguration cannot modify the host configuration because doing so could
        // change the environment, content root and application name which is not allowed at this stage.
        foreach (var configureAppAction in _configureAppActions)
        {
            configureAppAction(Context, _builder.Configuration);
        }
 
        foreach (var configureServicesAction in _configureServicesActions)
        {
            configureServicesAction(Context, _builder.Services);
        }
 
        ServiceDescriptor? genericWebHostServiceDescriptor = null;
 
        for (int i = _builder.Services.Count - 1; i >= 0; i--)
        {
            var descriptor = _builder.Services[i];
            if (descriptor.ServiceType == typeof(IHostedService))
            {
                Debug.Assert(descriptor.ImplementationType?.Name == "GenericWebHostService");
 
                genericWebHostServiceDescriptor = descriptor;
                _builder.Services.RemoveAt(i);
                break;
            }
        }
 
        return genericWebHostServiceDescriptor ?? throw new InvalidOperationException($"GenericWebHostedService must exist in the {nameof(IServiceCollection)}");
    }
}