// 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.ComponentModel.DataAnnotations;
using System.IO;
using System.Linq;
using System.Text.Encodings.Web;
using Microsoft.AspNetCore.Antiforgery;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.Abstractions;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.Routing;
using Microsoft.AspNetCore.Mvc.ViewEngines;
using Microsoft.AspNetCore.Routing;
using Microsoft.AspNetCore.Testing;
using Microsoft.Extensions.Options;
using Moq;
using Xunit;

namespace Microsoft.AspNetCore.Mvc.ViewFeatures
{
    public class DefaultHtmlGeneratorTest
    {
        [Theory]
        [InlineData(false)]
        [InlineData(true)]
        public void GetCurrentValues_WithEmptyViewData_ReturnsNull(bool allowMultiple)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);

            // Act
            var result = htmlGenerator.GetCurrentValues(
                viewContext,
                modelExplorer: null,
                expression: nameof(Model.Name),
                allowMultiple: allowMultiple);

            // Assert
            Assert.Null(result);
        }

        [Theory]
        [InlineData(false)]
        [InlineData(true)]
        public void GetCurrentValues_WithNullExpressionResult_ReturnsNull(bool allowMultiple)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);
            var modelExplorer = metadataProvider.GetModelExplorerForType(typeof(string), model: null);

            // Act
            var result = htmlGenerator.GetCurrentValues(
                viewContext,
                modelExplorer,
                expression: nameof(Model.Name),
                allowMultiple: allowMultiple);

            // Assert
            Assert.Null(result);
        }

        [Fact]
        public void GetCurrentValues_WithNullExpression_DoesNotThrow()
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);
            var modelExplorer = metadataProvider.GetModelExplorerForType(typeof(string), model: null);

            // Act and Assert (does not throw).
            htmlGenerator.GetCurrentValues(viewContext, modelExplorer, expression: null, allowMultiple: true);
        }

        [Fact]
        public void GenerateSelect_WithNullExpression_Throws()
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);
            var modelExplorer = metadataProvider.GetModelExplorerForType(typeof(string), model: null);

            var expected = "The name of an HTML field cannot be null or empty. Instead use methods " +
                "Microsoft.AspNetCore.Mvc.Rendering.IHtmlHelper.Editor or Microsoft.AspNetCore.Mvc.Rendering." +
                "IHtmlHelper`1.EditorFor with a non-empty htmlFieldName argument value.";

            // Act and Assert
            ExceptionAssert.ThrowsArgument(
                () => htmlGenerator.GenerateSelect(
                    viewContext,
                    modelExplorer,
                    "label",
                    expression: null,
                    selectList: new List<SelectListItem>(),
                    allowMultiple: true,
                    htmlAttributes: null),
                "expression",
                expected);
        }

        [Fact]
        public void GenerateSelect_WithNullExpression_WithNameAttribute_DoesNotThrow()
        {
            // Arrange
            var expected = "-expression-";
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);
            var modelExplorer = metadataProvider.GetModelExplorerForType(typeof(string), model: null);
            var htmlAttributes = new Dictionary<string, object>
            {
                { "name", expected },
            };

            // Act
            var tagBuilder = htmlGenerator.GenerateSelect(
                viewContext,
                modelExplorer,
                "label",
                expression: null,
                selectList: new List<SelectListItem>(),
                allowMultiple: true,
                htmlAttributes: htmlAttributes);

            // Assert
            var attribute = Assert.Single(tagBuilder.Attributes, a => a.Key == "name");
            Assert.Equal(expected, attribute.Value);
        }

        [Fact]
        public void GenerateTextArea_WithNullExpression_Throws()
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);
            var modelExplorer = metadataProvider.GetModelExplorerForType(typeof(string), model: null);

            var expected = "The name of an HTML field cannot be null or empty. Instead use methods " +
                "Microsoft.AspNetCore.Mvc.Rendering.IHtmlHelper.Editor or Microsoft.AspNetCore.Mvc.Rendering." +
                "IHtmlHelper`1.EditorFor with a non-empty htmlFieldName argument value.";

            // Act and Assert
            ExceptionAssert.ThrowsArgument(
                () => htmlGenerator.GenerateTextArea(
                    viewContext,
                    modelExplorer,
                    expression: null,
                    rows: 1,
                    columns: 1,
                    htmlAttributes: null),
                "expression",
                expected);
        }

        [Fact]
        public void GenerateTextArea_WithNullExpression_WithNameAttribute_DoesNotThrow()
        {
            // Arrange
            var expected = "-expression-";
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);
            var modelExplorer = metadataProvider.GetModelExplorerForType(typeof(string), model: null);
            var htmlAttributes = new Dictionary<string, object>
            {
                { "name", expected },
            };

            // Act
            var tagBuilder = htmlGenerator.GenerateTextArea(
                viewContext,
                modelExplorer,
                expression: null,
                rows: 1,
                columns: 1,
                htmlAttributes: htmlAttributes);

            // Assert
            var attribute = Assert.Single(tagBuilder.Attributes, a => a.Key == "name");
            Assert.Equal(expected, attribute.Value);
        }

        [Theory]
        [InlineData(nameof(ModelWithMaxLengthMetadata.FieldWithMaxLength), ModelWithMaxLengthMetadata.MaxLengthAttributeValue)]
        [InlineData(nameof(ModelWithMaxLengthMetadata.FieldWithStringLength), ModelWithMaxLengthMetadata.StringLengthAttributeValue)]
        public void GenerateTextArea_RendersMaxLength(string expression, int expectedValue)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<ModelWithMaxLengthMetadata>(model: null, metadataProvider: metadataProvider);
            var modelMetadata = metadataProvider.GetMetadataForProperty(typeof(ModelWithMaxLengthMetadata), expression);
            var modelExplorer = new ModelExplorer(metadataProvider, modelMetadata, null);
            var htmlAttributes = new Dictionary<string, object>
            {
                { "name", "testElement" },
            };

            // Act
            var tagBuilder = htmlGenerator.GenerateTextArea(viewContext, modelExplorer, expression, rows: 1, columns: 1, htmlAttributes);

            // Assert
            var attribute = Assert.Single(tagBuilder.Attributes, a => a.Key == "maxlength");
            Assert.Equal(expectedValue, Int32.Parse(attribute.Value));
        }

        [Theory]
        [InlineData(nameof(ModelWithMaxLengthMetadata.FieldWithMaxLength), ModelWithMaxLengthMetadata.MaxLengthAttributeValue)]
        [InlineData(nameof(ModelWithMaxLengthMetadata.FieldWithStringLength), ModelWithMaxLengthMetadata.StringLengthAttributeValue)]
        public void GeneratePassword_RendersMaxLength(string expression, int expectedValue)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<ModelWithMaxLengthMetadata>(model: null, metadataProvider: metadataProvider);
            var modelMetadata = metadataProvider.GetMetadataForProperty(typeof(ModelWithMaxLengthMetadata), expression);
            var modelExplorer = new ModelExplorer(metadataProvider, modelMetadata, null);
            var htmlAttributes = new Dictionary<string, object>
            {
                { "name", "testElement" },
            };

            // Act
            var tagBuilder = htmlGenerator.GeneratePassword(viewContext, modelExplorer, expression, null, htmlAttributes);

            // Assert
            var attribute = Assert.Single(tagBuilder.Attributes, a => a.Key == "maxlength");
            Assert.Equal(expectedValue, Int32.Parse(attribute.Value));
        }

        [Theory]
        [InlineData(nameof(ModelWithMaxLengthMetadata.FieldWithMaxLength), ModelWithMaxLengthMetadata.MaxLengthAttributeValue)]
        [InlineData(nameof(ModelWithMaxLengthMetadata.FieldWithStringLength), ModelWithMaxLengthMetadata.StringLengthAttributeValue)]
        public void GenerateTextBox_RendersMaxLength(string expression, int expectedValue)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<ModelWithMaxLengthMetadata>(model: null, metadataProvider: metadataProvider);
            var modelMetadata = metadataProvider.GetMetadataForProperty(typeof(ModelWithMaxLengthMetadata), expression);
            var modelExplorer = new ModelExplorer(metadataProvider, modelMetadata, null);
            var htmlAttributes = new Dictionary<string, object>
            {
                { "name", "testElement" },
            };

            // Act
            var tagBuilder = htmlGenerator.GenerateTextBox(viewContext, modelExplorer, expression, null, null, htmlAttributes);

            // Assert
            var attribute = Assert.Single(tagBuilder.Attributes, a => a.Key == "maxlength");
            Assert.Equal(expectedValue, Int32.Parse(attribute.Value));
        }

        [Fact]
        public void GenerateTextBox_RendersMaxLength_WithMinimumValueFromBothAttributes()
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<ModelWithMaxLengthMetadata>(model: null, metadataProvider: metadataProvider);
            var modelMetadata = metadataProvider.GetMetadataForProperty(typeof(ModelWithMaxLengthMetadata), nameof(ModelWithMaxLengthMetadata.FieldWithBothAttributes));
            var modelExplorer = new ModelExplorer(metadataProvider, modelMetadata, null);
            var htmlAttributes = new Dictionary<string, object>
            {
                { "name", "testElement" },
            };

            // Act
            var tagBuilder = htmlGenerator.GenerateTextBox(viewContext, modelExplorer, nameof(ModelWithMaxLengthMetadata.FieldWithBothAttributes), null, null, htmlAttributes);

            // Assert
            var attribute = Assert.Single(tagBuilder.Attributes, a => a.Key == "maxlength");
            Assert.Equal(Math.Min(ModelWithMaxLengthMetadata.MaxLengthAttributeValue, ModelWithMaxLengthMetadata.StringLengthAttributeValue), Int32.Parse(attribute.Value));
        }

        [Fact]
        public void GenerateTextBox_DoesNotRenderMaxLength_WhenNoAttributesPresent()
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<ModelWithMaxLengthMetadata>(model: null, metadataProvider: metadataProvider);
            var modelMetadata = metadataProvider.GetMetadataForProperty(typeof(ModelWithMaxLengthMetadata), nameof(ModelWithMaxLengthMetadata.FieldWithoutAttributes));
            var modelExplorer = new ModelExplorer(metadataProvider, modelMetadata, null);
            var htmlAttributes = new Dictionary<string, object>
            {
                { "name", "testElement" },
            };

            // Act
            var tagBuilder = htmlGenerator.GenerateTextBox(viewContext, modelExplorer, nameof(ModelWithMaxLengthMetadata.FieldWithoutAttributes), null, null, htmlAttributes);

            // Assert
            Assert.DoesNotContain(tagBuilder.Attributes, a => a.Key == "maxlength");
        }

        [Theory]
        [InlineData(nameof(ModelWithMaxLengthMetadata.FieldWithMaxLength), ModelWithMaxLengthMetadata.MaxLengthAttributeValue)]
        [InlineData(nameof(ModelWithMaxLengthMetadata.FieldWithStringLength), ModelWithMaxLengthMetadata.StringLengthAttributeValue)]
        public void GenerateTextBox_SearchType_RendersMaxLength(string expression, int expectedValue)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<ModelWithMaxLengthMetadata>(model: null, metadataProvider: metadataProvider);
            var modelMetadata = metadataProvider.GetMetadataForProperty(typeof(ModelWithMaxLengthMetadata), expression);
            var modelExplorer = new ModelExplorer(metadataProvider, modelMetadata, null);
            var htmlAttributes = new Dictionary<string, object>
            {
                { "name", "testElement" },
                { "type", "search"}
            };

            // Act
            var tagBuilder = htmlGenerator.GenerateTextBox(viewContext, modelExplorer, expression, null, null, htmlAttributes);

            // Assert
            var attribute = Assert.Single(tagBuilder.Attributes, a => a.Key == "maxlength");
            Assert.Equal(expectedValue, Int32.Parse(attribute.Value));
        }

        [Theory]
        [InlineData(nameof(ModelWithMaxLengthMetadata.FieldWithMaxLength))]
        [InlineData(nameof(ModelWithMaxLengthMetadata.FieldWithStringLength))]
        public void GenerateHidden_DoesNotRenderMaxLength(string expression)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<ModelWithMaxLengthMetadata>(model: null, metadataProvider: metadataProvider);
            var modelMetadata = metadataProvider.GetMetadataForProperty(typeof(ModelWithMaxLengthMetadata), expression);
            var modelExplorer = new ModelExplorer(metadataProvider, modelMetadata, null);
            var htmlAttributes = new Dictionary<string, object>
            {
                { "name", "testElement" },
            };

            // Act
            var tagBuilder = htmlGenerator.GenerateHidden(viewContext, modelExplorer, expression, null, false, htmlAttributes);

            // Assert
            Assert.DoesNotContain(tagBuilder.Attributes, a => a.Key == "maxlength");
        }

        [Fact]
        public void GenerateValidationMessage_WithNullExpression_Throws()
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);
            var modelExplorer = metadataProvider.GetModelExplorerForType(typeof(string), model: null);

            var expected = "The name of an HTML field cannot be null or empty. Instead use methods " +
                "Microsoft.AspNetCore.Mvc.Rendering.IHtmlHelper.Editor or Microsoft.AspNetCore.Mvc.Rendering." +
                "IHtmlHelper`1.EditorFor with a non-empty htmlFieldName argument value.";

            // Act and Assert
            ExceptionAssert.ThrowsArgument(
                () => htmlGenerator.GenerateValidationMessage(
                    viewContext,
                    modelExplorer: null,
                    expression: null,
                    message: "Message",
                    tag: "tag",
                    htmlAttributes: null),
                "expression",
                expected);
        }

        [Fact]
        public void GenerateValidationMessage_WithNullExpression_WithValidationForAttribute_DoesNotThrow()
        {
            // Arrange
            var expected = "-expression-";
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);
            var modelExplorer = metadataProvider.GetModelExplorerForType(typeof(string), model: null);
            var htmlAttributes = new Dictionary<string, object>
            {
                { "data-valmsg-for", expected },
            };

            // Act
            var tagBuilder = htmlGenerator.GenerateValidationMessage(
                viewContext,
                modelExplorer: null,
                expression: null,
                message: "Message",
                tag: "tag",
                htmlAttributes: htmlAttributes);

            // Assert
            var attribute = Assert.Single(tagBuilder.Attributes, a => a.Key == "data-valmsg-for");
            Assert.Equal(expected, attribute.Value);
        }

        [Theory]
        [InlineData(false)]
        [InlineData(true)]
        public void GetCurrentValues_WithSelectListInViewData_ReturnsNull(bool allowMultiple)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);
            viewContext.ViewData[nameof(Model.Name)] = Enumerable.Empty<SelectListItem>();

            // Act
            var result = htmlGenerator.GetCurrentValues(
                viewContext,
                modelExplorer: null,
                expression: nameof(Model.Name),
                allowMultiple: allowMultiple);

            // Assert
            Assert.Null(result);
        }

        [Theory]
        [InlineData("some string")] // treated as if it were not IEnumerable
        [InlineData(23)]
        [InlineData(RegularEnum.Three)]
        public void GetCurrentValues_AllowMultipleWithNonEnumerableInViewData_Throws(object value)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);
            viewContext.ViewData[nameof(Model.Name)] = value;

            // Act & Assert
            var exception = Assert.Throws<InvalidOperationException>(() => htmlGenerator.GetCurrentValues(
                viewContext,
                modelExplorer: null,
                expression: nameof(Model.Name),
                allowMultiple: true));
            Assert.Equal(
                "The parameter 'expression' must evaluate to an IEnumerable when multiple selection is allowed.",
                exception.Message);
        }

        // rawValue, allowMultiple -> expected current values
        public static TheoryData<string[], bool, IReadOnlyCollection<string>> GetCurrentValues_CollectionData
        {
            get
            {
                return new TheoryData<string[], bool, IReadOnlyCollection<string>>
                {
                    // ModelStateDictionary converts arrays to single values if needed.
                    { new [] { "some string" }, false, new [] { "some string" } },
                    { new [] { "some string" }, true, new [] { "some string" } },
                    { new [] { "some string", "some other string" }, false, new [] { "some string" } },
                    {
                        new [] { "some string", "some other string" },
                        true,
                        new [] { "some string", "some other string" }
                    },
                    // { new string[] { null }, false, null } would fall back to other sources.
                    { new string[] { null }, true, new [] { string.Empty } },
                    { new [] { string.Empty }, false, new [] { string.Empty } },
                    { new [] { string.Empty }, true, new [] { string.Empty } },
                    {
                        new [] { null, "some string", "some other string" },
                        true,
                        new [] { string.Empty, "some string", "some other string" }
                    },
                    // ignores duplicates
                    {
                        new [] { null, "some string", null, "some other string", null, "some string", null },
                        true,
                        new [] { string.Empty, "some string", "some other string" }
                    },
                    // ignores case of duplicates
                    {
                        new [] { "some string", "SoMe StriNg", "Some String", "soME STRing", "SOME STRING" },
                        true,
                        new [] { "some string" }
                    },
                };
            }
        }

        [Theory]
        [MemberData(nameof(GetCurrentValues_CollectionData))]
        public void GetCurrentValues_WithModelStateEntryAndViewData_ReturnsModelStateEntry(
            string[] rawValue,
            bool allowMultiple,
            IReadOnlyCollection<string> expected)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var model = new Model { Name = "ignored property value" };

            var viewContext = GetViewContext<Model>(model, metadataProvider);
            viewContext.ViewData[nameof(Model.Name)] = "ignored ViewData value";
            viewContext.ModelState.SetModelValue(nameof(Model.Name), rawValue, attemptedValue: null);

            // Act
            var result = htmlGenerator.GetCurrentValues(
                viewContext,
                modelExplorer: null,
                expression: nameof(Model.Name),
                allowMultiple: allowMultiple);

            // Assert
            Assert.NotNull(result);
            Assert.Equal<string>(expected, result);
        }

        [Theory]
        [MemberData(nameof(GetCurrentValues_CollectionData))]
        public void GetCurrentValues_WithModelStateEntryModelExplorerAndViewData_ReturnsModelStateEntry(
            string[] rawValue,
            bool allowMultiple,
            IReadOnlyCollection<string> expected)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var model = new Model { Name = "ignored property value" };

            var viewContext = GetViewContext<Model>(model, metadataProvider);
            viewContext.ViewData[nameof(Model.Name)] = "ignored ViewData value";
            viewContext.ModelState.SetModelValue(nameof(Model.Name), rawValue, attemptedValue: null);

            var modelExplorer = metadataProvider.GetModelExplorerForType(typeof(string), "ignored model value");

            // Act
            var result = htmlGenerator.GetCurrentValues(
                viewContext,
                modelExplorer,
                expression: nameof(Model.Name),
                allowMultiple: allowMultiple);

            // Assert
            Assert.NotNull(result);
            Assert.Equal<string>(expected, result);
        }

        // rawValue -> expected current values
        public static TheoryData<string[], string[]> GetCurrentValues_StringData
        {
            get
            {
                return new TheoryData<string[], string[]>
                {
                    // 1. If given a ModelExplorer, GetCurrentValues does not use ViewData even if expression result is
                    // null.
                    // 2. Otherwise if ViewData entry exists, GetCurrentValue does not fall back to ViewData.Model even
                    // if entry is null.
                    // 3. Otherwise, GetCurrentValue does not fall back anywhere else even if ViewData.Model is null.
                    { null, null },
                    { new string[] { string.Empty }, new [] { string.Empty } },
                    { new string[] { "some string" }, new [] { "some string" } },
                };
            }
        }

        [Theory]
        [MemberData(nameof(GetCurrentValues_StringData))]
        public void GetCurrentValues_WithModelExplorerAndViewData_ReturnsExpressionResult(
            string[] rawValue,
            IReadOnlyCollection<string> expected)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var model = new Model { Name = "ignored property value" };

            var viewContext = GetViewContext<Model>(model, metadataProvider);
            viewContext.ViewData[nameof(Model.Name)] = "ignored ViewData value";
            viewContext.ModelState.SetModelValue(nameof(Model.Name), rawValue, attemptedValue: null);

            var modelExplorer = metadataProvider.GetModelExplorerForType(typeof(string), rawValue);

            // Act
            var result = htmlGenerator.GetCurrentValues(
                viewContext,
                modelExplorer,
                expression: nameof(Model.Name),
                allowMultiple: false);

            // Assert
            Assert.Equal<string>(expected, result);
        }

        [Theory]
        [MemberData(nameof(GetCurrentValues_StringData))]
        public void GetCurrentValues_WithViewData_ReturnsViewDataEntry(
            string[] rawValue,
            IReadOnlyCollection<string> expected)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var model = new Model { Name = "ignored property value" };

            var viewContext = GetViewContext<Model>(model, metadataProvider);
            viewContext.ViewData[nameof(Model.Name)] = rawValue;
            viewContext.ModelState.SetModelValue(nameof(Model.Name), rawValue, attemptedValue: null);

            // Act
            var result = htmlGenerator.GetCurrentValues(
                viewContext,
                modelExplorer: null,
                expression: nameof(Model.Name),
                allowMultiple: false);

            // Assert
            Assert.Equal<string>(expected, result);
        }

        [Theory]
        [MemberData(nameof(GetCurrentValues_StringData))]
        public void GetCurrentValues_WithModel_ReturnsModel(string[] rawValue, IReadOnlyCollection<string> expected)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var model = new Model { Name = rawValue?[0] };

            var viewContext = GetViewContext<Model>(model, metadataProvider);
            viewContext.ModelState.SetModelValue(nameof(Model.Name), rawValue, attemptedValue: null);

            // Act
            var result = htmlGenerator.GetCurrentValues(
                viewContext,
                modelExplorer: null,
                expression: nameof(Model.Name),
                allowMultiple: false);

            // Assert
            Assert.Equal<string>(expected, result);
        }

        // rawValue -> expected current values
        public static TheoryData<string[], string[]> GetCurrentValues_StringCollectionData
        {
            get
            {
                return new TheoryData<string[], string[]>
                {
                    { new string[] { null }, new [] { string.Empty } },
                    { new [] { string.Empty }, new [] { string.Empty } },
                    { new [] { "some string" }, new [] { "some string" } },
                    { new [] { "some string", "some other string" }, new [] { "some string", "some other string" } },
                    {
                        new [] { null, "some string", "some other string" },
                        new [] { string.Empty, "some string", "some other string" }
                    },
                    // ignores duplicates
                    {
                        new [] { null, "some string", null, "some other string", null, "some string", null },
                        new [] { string.Empty, "some string", "some other string" }
                    },
                    // ignores case of duplicates
                    {
                        new [] { "some string", "SoMe StriNg", "Some String", "soME STRing", "SOME STRING" },
                        new [] { "some string" }
                    },
                };
            }
        }

        [Theory]
        [MemberData(nameof(GetCurrentValues_StringCollectionData))]
        public void GetCurrentValues_CollectionWithModelExplorerAndViewData_ReturnsExpressionResult(
            string[] rawValue,
            IReadOnlyCollection<string> expected)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var model = new Model { Collection = { "ignored property value" } };

            var viewContext = GetViewContext<Model>(model, metadataProvider);
            viewContext.ViewData[nameof(Model.Collection)] = new[] { "ignored ViewData value" };
            viewContext.ModelState.SetModelValue(nameof(Model.Collection), rawValue, attemptedValue: null);

            var modelExplorer =
                metadataProvider.GetModelExplorerForType(typeof(List<string>), new List<string>(rawValue));

            // Act
            var result = htmlGenerator.GetCurrentValues(
                viewContext,
                modelExplorer,
                expression: nameof(Model.Collection),
                allowMultiple: true);

            // Assert
            Assert.Equal<string>(expected, result);
        }

        [Theory]
        [MemberData(nameof(GetCurrentValues_StringCollectionData))]
        public void GetCurrentValues_CollectionWithViewData_ReturnsViewDataEntry(
            string[] rawValue,
            IReadOnlyCollection<string> expected)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var model = new Model { Collection = { "ignored property value" } };

            var viewContext = GetViewContext<Model>(model, metadataProvider);
            viewContext.ViewData[nameof(Model.Collection)] = rawValue;
            viewContext.ModelState.SetModelValue(nameof(Model.Collection), rawValue, attemptedValue: null);

            // Act
            var result = htmlGenerator.GetCurrentValues(
                viewContext,
                modelExplorer: null,
                expression: nameof(Model.Collection),
                allowMultiple: true);

            // Assert
            Assert.Equal<string>(expected, result);
        }

        [Theory]
        [MemberData(nameof(GetCurrentValues_StringCollectionData))]
        public void GetCurrentValues_CollectionWithModel_ReturnsModel(
            string[] rawValue,
            IReadOnlyCollection<string> expected)
        {
            // Arrange
            var metadataProvider = new TestModelMetadataProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var model = new Model();
            model.Collection.AddRange(rawValue);

            var viewContext = GetViewContext<Model>(model, metadataProvider);
            viewContext.ModelState.SetModelValue(
                nameof(Model.Collection),
                rawValue,
                attemptedValue: null);

            // Act
            var result = htmlGenerator.GetCurrentValues(
                viewContext,
                modelExplorer: null,
                expression: nameof(Model.Collection),
                allowMultiple: true);

            // Assert
            Assert.Equal<string>(expected, result);
        }

        // property name, rawValue -> expected current values
        public static TheoryData<string, object, string[]> GetCurrentValues_ValueToConvertData
        {
            get
            {
                return new TheoryData<string, object, string[]>
                {
                    { nameof(Model.FlagsEnum), FlagsEnum.All, new [] { "-1", "All" } },
                    { nameof(Model.FlagsEnum), FlagsEnum.FortyTwo, new [] { "42", "FortyTwo" } },
                    { nameof(Model.FlagsEnum), FlagsEnum.None, new [] { "0", "None" } },
                    { nameof(Model.FlagsEnum), FlagsEnum.Two, new [] { "2", "Two" } },
                    { nameof(Model.FlagsEnum), string.Empty, new [] { string.Empty } },
                    { nameof(Model.FlagsEnum), "All", new [] { "-1", "All" } },
                    { nameof(Model.FlagsEnum), "FortyTwo", new [] { "42", "FortyTwo" } },
                    { nameof(Model.FlagsEnum), "None", new [] { "0", "None" } },
                    { nameof(Model.FlagsEnum), "Two", new [] { "2", "Two" } },
                    { nameof(Model.FlagsEnum), "Two, Four", new [] { "Two, Four", "6" } },
                    { nameof(Model.FlagsEnum), "garbage", new [] { "garbage" } },
                    { nameof(Model.FlagsEnum), "0", new [] { "0", "None" } },
                    { nameof(Model.FlagsEnum), "   43", new [] { "   43", "43" } },
                    { nameof(Model.FlagsEnum), "-5   ", new [] { "-5   ", "-5" } },
                    { nameof(Model.FlagsEnum), 0, new [] { "0", "None" } },
                    { nameof(Model.FlagsEnum), 1, new [] { "1", "One" } },
                    { nameof(Model.FlagsEnum), 43, new [] { "43" } },
                    { nameof(Model.FlagsEnum), -5, new [] { "-5" } },
                    { nameof(Model.FlagsEnum), int.MaxValue, new [] { "2147483647" } },
                    { nameof(Model.FlagsEnum), (uint)int.MaxValue + 1, new [] { "2147483648" } },
                    { nameof(Model.FlagsEnum), uint.MaxValue, new [] { "4294967295" } },  // converted to string & used

                    { nameof(Model.Id), string.Empty, new [] { string.Empty } },
                    { nameof(Model.Id), "garbage", new [] { "garbage" } },                  // no compatibility checks
                    { nameof(Model.Id), "0", new [] { "0" } },
                    { nameof(Model.Id), "  43", new [] { "  43" } },
                    { nameof(Model.Id), "-5  ", new [] { "-5  " } },
                    { nameof(Model.Id), 0, new [] { "0" } },
                    { nameof(Model.Id), 1, new [] { "1" } },
                    { nameof(Model.Id), 43, new [] { "43" } },
                    { nameof(Model.Id), -5, new [] { "-5" } },
                    { nameof(Model.Id), int.MaxValue, new [] { "2147483647" } },
                    { nameof(Model.Id), (uint)int.MaxValue + 1, new [] { "2147483648" } },  // no limit checks
                    { nameof(Model.Id), uint.MaxValue, new [] { "4294967295" } },           // no limit checks

                    { nameof(Model.NullableEnum), RegularEnum.Zero, new [] { "0", "Zero" } },
                    { nameof(Model.NullableEnum), RegularEnum.One, new [] { "1", "One" } },
                    { nameof(Model.NullableEnum), RegularEnum.Two, new [] { "2", "Two" } },
                    { nameof(Model.NullableEnum), RegularEnum.Three, new [] { "3", "Three" } },
                    { nameof(Model.NullableEnum), string.Empty, new [] { string.Empty } },
                    { nameof(Model.NullableEnum), "Zero", new [] { "0", "Zero" } },
                    { nameof(Model.NullableEnum), "Two", new [] { "2", "Two" } },
                    { nameof(Model.NullableEnum), "One, Two", new [] { "One, Two", "3", "Three" } },
                    { nameof(Model.NullableEnum), "garbage", new [] { "garbage" } },
                    { nameof(Model.NullableEnum), "0", new [] { "0", "Zero" } },
                    { nameof(Model.NullableEnum), "   43", new [] { "   43", "43" } },
                    { nameof(Model.NullableEnum), "-5   ", new [] { "-5   ", "-5" } },
                    { nameof(Model.NullableEnum), 0, new [] { "0", "Zero" } },
                    { nameof(Model.NullableEnum), 1, new [] { "1", "One" } },
                    { nameof(Model.NullableEnum), 43, new [] { "43" } },
                    { nameof(Model.NullableEnum), -5, new [] { "-5" } },
                    { nameof(Model.NullableEnum), int.MaxValue, new [] { "2147483647" } },
                    { nameof(Model.NullableEnum), (uint)int.MaxValue + 1, new [] { "2147483648" } },
                    { nameof(Model.NullableEnum), uint.MaxValue, new [] { "4294967295" } },

                    { nameof(Model.RegularEnum), RegularEnum.Zero, new [] { "0", "Zero" } },
                    { nameof(Model.RegularEnum), RegularEnum.One, new [] { "1", "One" } },
                    { nameof(Model.RegularEnum), RegularEnum.Two, new [] { "2", "Two" } },
                    { nameof(Model.RegularEnum), RegularEnum.Three, new [] { "3", "Three" } },
                    { nameof(Model.RegularEnum), string.Empty, new [] { string.Empty } },
                    { nameof(Model.RegularEnum), "Zero", new [] { "0", "Zero" } },
                    { nameof(Model.RegularEnum), "Two", new [] { "2", "Two" } },
                    { nameof(Model.RegularEnum), "One, Two", new [] { "One, Two", "3", "Three" } },
                    { nameof(Model.RegularEnum), "garbage", new [] { "garbage" } },
                    { nameof(Model.RegularEnum), "0", new [] { "0", "Zero" } },
                    { nameof(Model.RegularEnum), "   43", new [] { "   43", "43" } },
                    { nameof(Model.RegularEnum), "-5   ", new [] { "-5   ", "-5" } },
                    { nameof(Model.RegularEnum), 0, new [] { "0", "Zero" } },
                    { nameof(Model.RegularEnum), 1, new [] { "1", "One" } },
                    { nameof(Model.RegularEnum), 43, new [] { "43" } },
                    { nameof(Model.RegularEnum), -5, new [] { "-5" } },
                    { nameof(Model.RegularEnum), int.MaxValue, new [] { "2147483647" } },
                    { nameof(Model.RegularEnum), (uint)int.MaxValue + 1, new [] { "2147483648" } },
                    { nameof(Model.RegularEnum), uint.MaxValue, new [] { "4294967295" } },
                };
            }
        }

        [Theory]
        [MemberData(nameof(GetCurrentValues_ValueToConvertData))]
        public void GetCurrentValues_ValueConvertedAsExpected(
            string propertyName,
            object rawValue,
            IReadOnlyCollection<string> expected)
        {
            // Arrange
            var metadataProvider = TestModelMetadataProvider.CreateDefaultProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);
            viewContext.ModelState.SetModelValue(
                propertyName,
                new string[] { rawValue.ToString() },
                attemptedValue: null);

            // Act
            var result = htmlGenerator.GetCurrentValues(
                viewContext,
                modelExplorer: null,
                expression: propertyName,
                allowMultiple: false);

            // Assert
            Assert.Equal<string>(expected, result);
        }

        [Theory]
        [InlineData(true, "")]
        [InlineData(false, "<input name=\"formFieldName\" type=\"hidden\" value=\"requestToken\" />")]
        public void GenerateAntiforgery_GeneratesAntiforgeryFieldsOnlyIfRequired(
            bool hasAntiforgeryToken,
            string expectedAntiforgeryHtmlField)
        {
            // Arrange
            var metadataProvider = TestModelMetadataProvider.CreateDefaultProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);
            viewContext.FormContext.CanRenderAtEndOfForm = true;
            viewContext.FormContext.HasAntiforgeryToken = hasAntiforgeryToken;

            // Act
            var result = htmlGenerator.GenerateAntiforgery(viewContext);

            // Assert
            var antiforgeryField = HtmlContentUtilities.HtmlContentToString(result, HtmlEncoder.Default);
            Assert.Equal(expectedAntiforgeryHtmlField, antiforgeryField);
        }

        // This test covers use of the helper within literal <form> tags when tag helpers are not enabled e.g.
        // <form action="/Home/Create">
        //     @Html.AntiForgeryToken()
        // </form>
        [Theory]
        [InlineData(false)]
        [InlineData(true)]
        public void GenerateAntiforgery_AlwaysGeneratesAntiforgeryToken_IfCannotRenderAtEnd(bool hasAntiforgeryToken)
        {
            // Arrange
            var expected = "<input name=\"formFieldName\" type=\"hidden\" value=\"requestToken\" />";
            var metadataProvider = TestModelMetadataProvider.CreateDefaultProvider();
            var htmlGenerator = GetGenerator(metadataProvider);
            var viewContext = GetViewContext<Model>(model: null, metadataProvider: metadataProvider);
            viewContext.FormContext.HasAntiforgeryToken = hasAntiforgeryToken;

            // Act
            var result = htmlGenerator.GenerateAntiforgery(viewContext);

            // Assert
            var antiforgeryField = HtmlContentUtilities.HtmlContentToString(result, HtmlEncoder.Default);
            Assert.Equal(expected, antiforgeryField);
        }

        // GetCurrentValues uses only the IModelMetadataProvider passed to the DefaultHtmlGenerator constructor.
        private static IHtmlGenerator GetGenerator(IModelMetadataProvider metadataProvider)
        {
            var mvcViewOptionsAccessor = new Mock<IOptions<MvcViewOptions>>();
            mvcViewOptionsAccessor.SetupGet(accessor => accessor.Value).Returns(new MvcViewOptions() { AllowRenderingMaxLengthAttribute = true });

            var htmlEncoder = Mock.Of<HtmlEncoder>();
            var antiforgery = new Mock<IAntiforgery>();
            antiforgery
                .Setup(mock => mock.GetAndStoreTokens(It.IsAny<DefaultHttpContext>()))
                .Returns(() =>
                {
                    return new AntiforgeryTokenSet("requestToken", "cookieToken", "formFieldName", "headerName");
                });

            var attributeProvider = new DefaultValidationHtmlAttributeProvider(
                mvcViewOptionsAccessor.Object,
                metadataProvider,
                new ClientValidatorCache());

            return new DefaultHtmlGenerator(
                antiforgery.Object,
                mvcViewOptionsAccessor.Object,
                metadataProvider,
                new UrlHelperFactory(),
                htmlEncoder,
                attributeProvider);
        }

        // GetCurrentValues uses only the ModelStateDictionary and ViewDataDictionary from the passed ViewContext.
        private static ViewContext GetViewContext<TModel>(TModel model, IModelMetadataProvider metadataProvider)
        {
            var actionContext = new ActionContext(new DefaultHttpContext(), new RouteData(), new ActionDescriptor());
            var viewData = new ViewDataDictionary<TModel>(metadataProvider, actionContext.ModelState)
            {
                Model = model,
            };

            return new ViewContext(
                actionContext,
                Mock.Of<IView>(),
                viewData,
                Mock.Of<ITempDataDictionary>(),
                TextWriter.Null,
                new HtmlHelperOptions());
        }

        public enum RegularEnum
        {
            Zero,
            One,
            Two,
            Three,
        }

        public enum FlagsEnum
        {
            None = 0,
            One = 1,
            Two = 2,
            Four = 4,
            FortyTwo = 42,
            All = -1,
        }

        private class ModelWithMaxLengthMetadata
        {
            internal const int MaxLengthAttributeValue = 77;
            internal const int StringLengthAttributeValue = 7;

            [MaxLength(MaxLengthAttributeValue)]
            public string FieldWithMaxLength { get; set; }

            [StringLength(StringLengthAttributeValue)]
            public string FieldWithStringLength { get; set; }

            public string FieldWithoutAttributes { get; set; }

            [MaxLength(MaxLengthAttributeValue)]
            [StringLength(StringLengthAttributeValue)]
            public string FieldWithBothAttributes { get; set; }
        }

        private class Model
        {
            public int Id { get; set; }

            public string Name { get; set; }

            public RegularEnum RegularEnum { get; set; }

            public FlagsEnum FlagsEnum { get; set; }

            public RegularEnum? NullableEnum { get; set; }

            public List<string> Collection { get; } = new List<string>();
        }
    }
}