// 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.Collections;
using System.Collections.Generic;
using System.Diagnostics;

namespace Microsoft.Extensions.DependencyInjection
{
    /// <summary>
    /// Default implementation of <see cref="IServiceCollection"/>.
    /// </summary>
    [DebuggerDisplay("{DebuggerToString(),nq}")]
    [DebuggerTypeProxy(typeof(ServiceCollectionDebugView))]
    public class ServiceCollection : IServiceCollection
    {
        private readonly List<ServiceDescriptor> _descriptors = new List<ServiceDescriptor>();
        private bool _isReadOnly;

        /// <inheritdoc />
        public int Count => _descriptors.Count;

        /// <inheritdoc />
        public bool IsReadOnly => _isReadOnly;

        /// <inheritdoc />
        public ServiceDescriptor this[int index]
        {
            get
            {
                return _descriptors[index];
            }
            set
            {
                CheckReadOnly();
                _descriptors[index] = value;
            }
        }

        /// <inheritdoc />
        public void Clear()
        {
            CheckReadOnly();
            _descriptors.Clear();
        }

        /// <inheritdoc />
        public bool Contains(ServiceDescriptor item)
        {
            return _descriptors.Contains(item);
        }

        /// <inheritdoc />
        public void CopyTo(ServiceDescriptor[] array, int arrayIndex)
        {
            _descriptors.CopyTo(array, arrayIndex);
        }

        /// <inheritdoc />
        public bool Remove(ServiceDescriptor item)
        {
            CheckReadOnly();
            return _descriptors.Remove(item);
        }

        /// <inheritdoc />
        public IEnumerator<ServiceDescriptor> GetEnumerator()
        {
            return _descriptors.GetEnumerator();
        }

        void ICollection<ServiceDescriptor>.Add(ServiceDescriptor item)
        {
            CheckReadOnly();
            _descriptors.Add(item);
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }

        /// <inheritdoc />
        public int IndexOf(ServiceDescriptor item)
        {
            return _descriptors.IndexOf(item);
        }

        /// <inheritdoc />
        public void Insert(int index, ServiceDescriptor item)
        {
            CheckReadOnly();
            _descriptors.Insert(index, item);
        }

        /// <inheritdoc />
        public void RemoveAt(int index)
        {
            CheckReadOnly();
            _descriptors.RemoveAt(index);
        }

        /// <summary>
        /// Makes this collection read-only.
        /// </summary>
        /// <remarks>
        /// After the collection is marked as read-only, any further attempt to modify it throws an <see cref="InvalidOperationException" />.
        /// </remarks>
        public void MakeReadOnly()
        {
            _isReadOnly = true;
        }

        private void CheckReadOnly()
        {
            if (_isReadOnly)
            {
                ThrowReadOnlyException();
            }
        }

        private static void ThrowReadOnlyException() =>
            throw new InvalidOperationException(SR.ServiceCollectionReadOnly);

        private string DebuggerToString()
        {
            string debugText = $"Count = {_descriptors.Count}";
            if (_isReadOnly)
            {
                debugText += $", IsReadOnly = true";
            }
            return debugText;
        }

        private sealed class ServiceCollectionDebugView
        {
            private readonly ServiceCollection _services;

            public ServiceCollectionDebugView(ServiceCollection services)
            {
                _services = services;
            }

            [DebuggerBrowsable(DebuggerBrowsableState.RootHidden)]
            public ServiceDescriptor[] Items
            {
                get
                {
                    ServiceDescriptor[] items = new ServiceDescriptor[_services.Count];
                    _services.CopyTo(items, 0);
                    return items;
                }
            }
        }
    }
}