// 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.Linq.Expressions;
using Xunit;

namespace Microsoft.AspNetCore.Mvc.ViewFeatures
{
    public class MemberExpressionCacheKeyComparerTest
    {
        private readonly MemberExpressionCacheKeyComparer Comparer = MemberExpressionCacheKeyComparer.Instance;

        [Fact]
        public void Equals_ReturnsTrue_ForTheSameExpression()
        {
            // Arrange
            var key = GetKey(m => m.Value);

            // Act & Assert
            VerifyEquals(key, key);
        }

        [Fact]
        public void Equals_ReturnsTrue_ForDifferentInstances_OfSameExpression()
        {
            // Arrange
            var key1 = GetKey(m => m.Value);
            var key2 = GetKey(m => m.Value);

            // Act & Assert
            VerifyEquals(key1, key2);
        }

        [Fact]
        public void Equals_ReturnsTrue_ForChainedMemberAccessExpressionsWithReferenceTypes()
        {
            // Arrange
            var key1 = GetKey(m => m.TestModel2.Name);
            var key2 = GetKey(m => m.TestModel2.Name);

            // Act & Assert
            VerifyEquals(key1, key2);
        }

        [Fact]
        public void Equals_ReturnsTrue_ForChainedMemberAccessExpressionsWithNullableValueTypes()
        {
            // Arrange
            var key1 = GetKey(m => m.NullableDateTime.Value.TimeOfDay);
            var key2 = GetKey(m => m.NullableDateTime.Value.TimeOfDay);

            // Act & Assert
            VerifyEquals(key1, key2);
        }

        [Fact]
        public void Equals_ReturnsTrue_ForChainedMemberAccessExpressionsWithValueTypes()
        {
            // Arrange
            var key1 = GetKey(m => m.DateTime.Year);
            var key2 = GetKey(m => m.DateTime.Year);

            // Act & Assert
            VerifyEquals(key1, key2);
        }

        [Fact]
        public void Equals_ReturnsFalse_ForDifferentExpression()
        {
            // Arrange
            var key1 = GetKey(m => m.Value);
            var key2 = GetKey(m => m.TestModel2.Name);

            // Act & Assert
            VerifyNotEquals(key1, key2);
        }

        [Fact]
        public void Equals_ReturnsFalse_ForChainedExpressions()
        {
            // Arrange
            var key1 = GetKey(m => m.TestModel2.Id);
            var key2 = GetKey(m => m.TestModel2.Name);

            // Act & Assert
            VerifyNotEquals(key1, key2);
        }

        [Fact]
        public void Equals_ReturnsFalse_ForChainedExpressions_WithValueTypes()
        {
            // Arrange
            var key1 = GetKey(m => m.DateTime.Ticks);
            var key2 = GetKey(m => m.DateTime.Year);

            // Act & Assert
            VerifyNotEquals(key1, key2);
        }

        [Fact]
        public void Equals_ReturnsFalse_ForChainedExpressions_DifferingByNullable()
        {
            // Arrange
            var key1 = GetKey(m => m.DateTime.Ticks);
            var key2 = GetKey(m => m.NullableDateTime.Value.Ticks);

            // Act & Assert
            VerifyNotEquals(key1, key2);
        }

        [Fact]
        public void Equals_ReturnsFalse_WhenOneExpressionIsSubsetOfOther()
        {
            // Arrange
            var key1 = GetKey(m => m.TestModel2);
            var key2 = GetKey(m => m.TestModel2.Name);

            // Act & Assert
            VerifyNotEquals(key1, key2);
        }

        [Fact]
        public void Equals_ReturnsFalse_WhenMemberIsAccessedThroughNullableProperty()
        {
            // Arrange
            var key1 = GetKey(m => m.NullableDateTime.Value.Year);
            var key2 = GetKey(m => m.DateTime.Year);

            // Act
            VerifyNotEquals(key1, key2);
        }

        [Fact]
        public void Equals_ReturnsFalse_WhenMemberIsAccessedThroughDifferentModels()
        {
            // Arrange
            var key1 = GetKey<TestModel2, int>(m => m.Id);
            var key2 = GetKey(m => m.TestModel2.Id);

            // Act
            VerifyNotEquals(key1, key2);
        }

        [Fact]
        public void Equals_ReturnsFalse_WhenMemberIsAccessedThroughConstantExpression()
        {
            // Arrange
            var testModel = new TestModel2 { Id = 1 };
            var key1 = GetKey(m => testModel.Id);
            var key2 = GetKey<TestModel2, int>(m => m.Id);

            // Act
            VerifyNotEquals(key1, key2);
        }

        private void VerifyEquals(MemberExpressionCacheKey key1, MemberExpressionCacheKey key2)
        {
            Assert.Equal(key1, key2, Comparer);

            var hashCode1 = Comparer.GetHashCode(key1);
            var hashCode2 = Comparer.GetHashCode(key2);
            Assert.Equal(hashCode1, hashCode2);

            var cachedKey1 = key1.MakeCacheable();

            Assert.Equal(key1, cachedKey1, Comparer);
            Assert.Equal(cachedKey1, key1, Comparer);

            var cachedKeyHashCode1 = Comparer.GetHashCode(cachedKey1);
            Assert.Equal(hashCode1, cachedKeyHashCode1);
        }

        private void VerifyNotEquals(MemberExpressionCacheKey key1, MemberExpressionCacheKey key2)
        {
            var hashCode1 = Comparer.GetHashCode(key1);
            var hashCode2 = Comparer.GetHashCode(key2);

            Assert.NotEqual(hashCode1, hashCode2);
            Assert.NotEqual(key1, key2, Comparer);

            var cachedKey1 = key1.MakeCacheable();
            Assert.NotEqual(key2, cachedKey1, Comparer);

            var cachedKeyHashCode1 = Comparer.GetHashCode(cachedKey1);
            Assert.NotEqual(cachedKeyHashCode1, hashCode2);
        }

        private static MemberExpressionCacheKey GetKey<TResult>(Expression<Func<TestModel, TResult>> expression)
            => GetKey<TestModel, TResult>(expression);

        private static MemberExpressionCacheKey GetKey<TModel, TResult>(Expression<Func<TModel, TResult>> expression)
        {
            var memberExpression = Assert.IsAssignableFrom<MemberExpression>(expression.Body);
            return new MemberExpressionCacheKey(typeof(TModel), memberExpression);
        }

        public class TestModel
        {
            public string Value { get; set; }

            public TestModel2 TestModel2 { get; set; }

            public DateTime DateTime { get; set; }

            public DateTime? NullableDateTime { get; set; }
        }

        public class TestModel2
        {
            public string Name { get; set; }

            public int Id { get; set; }
        }
    }
}