// 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.Collections.Generic;
using System.Linq;
using Xunit;

namespace Microsoft.Extensions.Internal
{
    public class CopyOnWriteDictionaryHolderTest
    {
        [Fact]
        public void ReadOperation_DelegatesToSourceDictionary_IfNoMutationsArePerformed()
        {
            // Arrange
            var source = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase)
            {
                { "test-key", "test-value" },
                { "key2", "key2-value" }
            };

            var holder = new CopyOnWriteDictionaryHolder<string, object>(source);

            // Act and Assert
            Assert.Equal("key2-value", holder["key2"]);
            Assert.Equal(2, holder.Count);
            Assert.Equal(new string[] { "test-key", "key2" }, holder.Keys.ToArray());
            Assert.Equal(new object[] { "test-value", "key2-value" }, holder.Values.ToArray());
            Assert.True(holder.ContainsKey("test-key"));

            object value;
            Assert.False(holder.TryGetValue("different-key", out value));

            Assert.False(holder.HasBeenCopied);
            Assert.Same(source, holder.ReadDictionary);
        }

        [Fact]
        public void ReadOperation_DoesNotDelegateToSourceDictionary_OnceAValueIsChanged()
        {
            // Arrange
            var source = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase)
            {
                { "key1", "value1" },
                { "key2", "value2" }
            };

            var holder = new CopyOnWriteDictionaryHolder<string, object>(source);

            // Act
            holder["key2"] = "value3";

            // Assert
            Assert.Equal("value2", source["key2"]);
            Assert.Equal(2, holder.Count);
            Assert.Equal("value1", holder["key1"]);
            Assert.Equal("value3", holder["key2"]);

            Assert.True(holder.HasBeenCopied);
            Assert.NotSame(source, holder.ReadDictionary);
        }

        [Fact]
        public void ReadOperation_DoesNotDelegateToSourceDictionary_OnceValueIsAdded()
        {
            // Arrange
            var source = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase)
            {
                { "key1", "value1" },
                { "key2", "value2" }
            };

            var holder = new CopyOnWriteDictionaryHolder<string, object>(source);

            // Act
            holder.Add("key3", "value3");
            holder.Remove("key1");

            // Assert
            Assert.Equal(2, source.Count);
            Assert.Equal("value1", source["key1"]);
            Assert.Equal(2, holder.Count);
            Assert.Equal("value2", holder["KeY2"]);
            Assert.Equal("value3", holder["key3"]);

            Assert.True(holder.HasBeenCopied);
            Assert.NotSame(source, holder.ReadDictionary);
        }
    }
}
