namespace StellaOps.Microservice.Tests;

/// <summary>
/// Unit tests for <see cref="HeaderCollection"/>.
/// </summary>
public sealed class HeaderCollectionTests
{
    #region Constructor Tests

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Constructor_Default_CreatesEmptyCollection()
    {
        // Arrange & Act
        var headers = new HeaderCollection();

        // Assert
        headers.Should().BeEmpty();
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Constructor_WithKeyValuePairs_AddsAllHeaders()
    {
        // Arrange
        var pairs = new[]
        {
            new KeyValuePair<string, string>("Content-Type", "application/json"),
            new KeyValuePair<string, string>("Accept", "application/json")
        };

        // Act
        var headers = new HeaderCollection(pairs);

        // Assert
        headers["Content-Type"].Should().Be("application/json");
        headers["Accept"].Should().Be("application/json");
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Constructor_WithDuplicateKeys_AddsMultipleValues()
    {
        // Arrange
        var pairs = new[]
        {
            new KeyValuePair<string, string>("Accept", "application/json"),
            new KeyValuePair<string, string>("Accept", "text/plain")
        };

        // Act
        var headers = new HeaderCollection(pairs);

        // Assert
        headers.GetValues("Accept").Should().BeEquivalentTo(["application/json", "text/plain"]);
    }

    #endregion

    #region Empty Tests

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Empty_IsSharedInstance()
    {
        // Arrange & Act
        var empty1 = HeaderCollection.Empty;
        var empty2 = HeaderCollection.Empty;

        // Assert
        empty1.Should().BeSameAs(empty2);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Empty_HasNoHeaders()
    {
        // Arrange & Act
        var empty = HeaderCollection.Empty;

        // Assert
        empty.Should().BeEmpty();
    }

    #endregion

    #region Indexer Tests

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Indexer_ExistingKey_ReturnsFirstValue()
    {
        // Arrange
        var headers = new HeaderCollection();
        headers.Add("Content-Type", "application/json");

        // Act
        var value = headers["Content-Type"];

        // Assert
        value.Should().Be("application/json");
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Indexer_MultipleValues_ReturnsFirstValue()
    {
        // Arrange
        var headers = new HeaderCollection();
        headers.Add("Accept", "application/json");
        headers.Add("Accept", "text/plain");

        // Act
        var value = headers["Accept"];

        // Assert
        value.Should().Be("application/json");
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Indexer_NonexistentKey_ReturnsNull()
    {
        // Arrange
        var headers = new HeaderCollection();

        // Act
        var value = headers["X-Missing"];

        // Assert
        value.Should().BeNull();
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Indexer_IsCaseInsensitive()
    {
        // Arrange
        var headers = new HeaderCollection();
        headers.Add("Content-Type", "application/json");

        // Act & Assert
        headers["content-type"].Should().Be("application/json");
        headers["CONTENT-TYPE"].Should().Be("application/json");
        headers["Content-TYPE"].Should().Be("application/json");
    }

    #endregion

    #region Add Tests

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Add_NewKey_AddsHeader()
    {
        // Arrange
        var headers = new HeaderCollection();

        // Act
        headers.Add("Content-Type", "application/json");

        // Assert
        headers["Content-Type"].Should().Be("application/json");
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Add_ExistingKey_AppendsValue()
    {
        // Arrange
        var headers = new HeaderCollection();
        headers.Add("Accept", "application/json");

        // Act
        headers.Add("Accept", "text/plain");

        // Assert
        headers.GetValues("Accept").Should().HaveCount(2);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Add_CaseInsensitiveKey_AppendsToExisting()
    {
        // Arrange
        var headers = new HeaderCollection();
        headers.Add("Content-Type", "application/json");

        // Act
        headers.Add("content-type", "text/plain");

        // Assert
        headers.GetValues("Content-Type").Should().HaveCount(2);
    }

    #endregion

    #region Set Tests

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Set_NewKey_AddsHeader()
    {
        // Arrange
        var headers = new HeaderCollection();

        // Act
        headers.Set("Content-Type", "application/json");

        // Assert
        headers["Content-Type"].Should().Be("application/json");
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Set_ExistingKey_ReplacesValue()
    {
        // Arrange
        var headers = new HeaderCollection();
        headers.Add("Content-Type", "text/plain");
        headers.Add("Content-Type", "text/html");

        // Act
        headers.Set("Content-Type", "application/json");

        // Assert
        headers.GetValues("Content-Type").Should().BeEquivalentTo(["application/json"]);
    }

    #endregion

    #region GetValues Tests

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void GetValues_ExistingKey_ReturnsAllValues()
    {
        // Arrange
        var headers = new HeaderCollection();
        headers.Add("Accept", "application/json");
        headers.Add("Accept", "text/plain");
        headers.Add("Accept", "text/html");

        // Act
        var values = headers.GetValues("Accept");

        // Assert
        values.Should().BeEquivalentTo(["application/json", "text/plain", "text/html"]);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void GetValues_NonexistentKey_ReturnsEmptyEnumerable()
    {
        // Arrange
        var headers = new HeaderCollection();

        // Act
        var values = headers.GetValues("X-Missing");

        // Assert
        values.Should().BeEmpty();
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void GetValues_IsCaseInsensitive()
    {
        // Arrange
        var headers = new HeaderCollection();
        headers.Add("Accept", "application/json");

        // Act & Assert
        headers.GetValues("accept").Should().Contain("application/json");
        headers.GetValues("ACCEPT").Should().Contain("application/json");
    }

    #endregion

    #region TryGetValue Tests

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void TryGetValue_ExistingKey_ReturnsTrueAndValue()
    {
        // Arrange
        var headers = new HeaderCollection();
        headers.Add("Content-Type", "application/json");

        // Act
        var result = headers.TryGetValue("Content-Type", out var value);

        // Assert
        result.Should().BeTrue();
        value.Should().Be("application/json");
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void TryGetValue_NonexistentKey_ReturnsFalse()
    {
        // Arrange
        var headers = new HeaderCollection();

        // Act
        var result = headers.TryGetValue("X-Missing", out var value);

        // Assert
        result.Should().BeFalse();
        value.Should().BeNull();
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void TryGetValue_IsCaseInsensitive()
    {
        // Arrange
        var headers = new HeaderCollection();
        headers.Add("Content-Type", "application/json");

        // Act
        var result = headers.TryGetValue("content-type", out var value);

        // Assert
        result.Should().BeTrue();
        value.Should().Be("application/json");
    }

    #endregion

    #region ContainsKey Tests

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void ContainsKey_ExistingKey_ReturnsTrue()
    {
        // Arrange
        var headers = new HeaderCollection();
        headers.Add("Content-Type", "application/json");

        // Act & Assert
        headers.ContainsKey("Content-Type").Should().BeTrue();
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void ContainsKey_NonexistentKey_ReturnsFalse()
    {
        // Arrange
        var headers = new HeaderCollection();

        // Act & Assert
        headers.ContainsKey("X-Missing").Should().BeFalse();
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void ContainsKey_IsCaseInsensitive()
    {
        // Arrange
        var headers = new HeaderCollection();
        headers.Add("Content-Type", "application/json");

        // Act & Assert
        headers.ContainsKey("content-type").Should().BeTrue();
        headers.ContainsKey("CONTENT-TYPE").Should().BeTrue();
    }

    #endregion

    #region Enumeration Tests

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void GetEnumerator_EnumeratesAllHeaderValues()
    {
        // Arrange
        var headers = new HeaderCollection();
        headers.Add("Content-Type", "application/json");
        headers.Add("Accept", "text/plain");
        headers.Add("Accept", "text/html");

        // Act
        var list = headers.ToList();

        // Assert
        list.Should().HaveCount(3);
        list.Should().Contain(kvp => kvp.Key == "Content-Type" && kvp.Value == "application/json");
        list.Should().Contain(kvp => kvp.Key == "Accept" && kvp.Value == "text/plain");
        list.Should().Contain(kvp => kvp.Key == "Accept" && kvp.Value == "text/html");
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void GetEnumerator_EmptyCollection_EnumeratesNothing()
    {
        // Arrange
        var headers = new HeaderCollection();

        // Act
        var list = headers.ToList();

        // Assert
        list.Should().BeEmpty();
    }

    #endregion
}