using System.Globalization;
using System.IO;
using System.Linq;
using System.Text;
using System.Xml.Linq;

using SongTidy.Models;
using SongTidy.Services;

namespace SongTidy.Tests;

/// <summary>
/// Contains tests for <see cref="PlanXmlIO"/>.
/// </summary>
[TestClass]
public sealed class PlanXmlIOTests {
    #region Document structure

    /// <summary>
    /// Verifies the generated XML root, version, format, and item attributes.
    /// </summary>
    [TestMethod]
    public void SavesExpectedDocumentStructure() {
        SongPlan plan = CreateSamplePlan();

        string xml = SaveToString(plan);
        XDocument document = XDocument.Parse(xml);
        XElement root = document.Root!;

        Assert.AreEqual("Plan", root.Name.LocalName);
        Assert.AreEqual(SongPlan.CurrentVersion.ToString(CultureInfo.InvariantCulture), root.Attribute("version")?.Value);
        Assert.HasCount(1, root.Attributes());
        Assert.AreEqual("ArtistFirst", root.Element("Format")?.Value);

        XElement items = root.Element("Items")!;
        Assert.HasCount(2, items.Elements("Item"));

        XElement first = items.Elements("Item").First();
        Assert.AreEqual(@"D:\Music\A - B (Live).mp3", first.Attribute("Path")?.Value);
        Assert.AreEqual("A", first.Attribute("Artist")?.Value);
        Assert.AreEqual("B", first.Attribute("Title")?.Value);
        Assert.AreEqual("Live", first.Attribute("Comment")?.Value);

        Assert.IsTrue(
            xml.StartsWith("<?xml version=\"1.0\" encoding=\"utf-8\"?>", StringComparison.Ordinal),
            "The XML declaration should specify UTF-8.");
    }

    /// <summary>
    /// Verifies that empty fields are still written as empty attributes.
    /// </summary>
    [TestMethod]
    public void WritesEmptyFieldsAsAttributes() {
        SongPlan plan = new() {
            Items = new List<PlanItem> {
                new PlanItem {
                    Path = @"C:\Music\C.mp3",
                    Title = "C",
                },
            },
        };

        string xml = SaveToString(plan);
        XElement item = XDocument.Parse(xml).Root!.Element("Items")!.Element("Item")!;

        Assert.IsNotNull(item.Attribute("Artist"));
        Assert.AreEqual(string.Empty, item.Attribute("Artist")!.Value);
        Assert.IsNotNull(item.Attribute("Comment"));
        Assert.AreEqual(string.Empty, item.Attribute("Comment")!.Value);
    }

    #endregion

    #region Round trips

    /// <summary>
    /// Verifies that both format enum values survive a round trip.
    /// </summary>
    /// <param name="format">The format to round-trip.</param>
    [TestMethod]
    [DataRow(RenameFormat.ArtistFirst)]
    [DataRow(RenameFormat.TitleFirst)]
    public void RoundTripsFormat(RenameFormat format) {
        SongPlan plan = new() {
            Format = format,
            Items = new List<PlanItem> {
                new PlanItem { Path = @"C:\Music\C.mp3", Title = "C" },
            },
        };

        SongPlan loaded = RoundTrip(plan);

        Assert.AreEqual(format, loaded.Format);
    }

    /// <summary>
    /// Verifies that every field and the version survive a round trip.
    /// </summary>
    [TestMethod]
    public void RoundTripsAllFields() {
        SongPlan plan = CreateSamplePlan();

        SongPlan loaded = RoundTrip(plan);

        Assert.AreEqual(plan.Version, loaded.Version);
        Assert.AreEqual(plan.Format, loaded.Format);
        Assert.HasCount(2, loaded.Items);
        AssertPlanItem(plan.Items[0], loaded.Items[0]);
        AssertPlanItem(plan.Items[1], loaded.Items[1]);
    }

    /// <summary>
    /// Verifies that a non-default version attribute is preserved.
    /// </summary>
    [TestMethod]
    public void PreservesVersion() {
        SongPlan plan = CreateSamplePlan();
        int version = SongPlan.CurrentVersion + 1;
        plan.Version = version;

        SongPlan loaded = RoundTrip(plan);

        Assert.AreEqual(version, loaded.Version);
    }

    /// <summary>
    /// Verifies that paths and fields containing spaces and XML special characters round-trip.
    /// </summary>
    [TestMethod]
    public void RoundTripsPathsWithSpacesAndSpecialCharacters() {
        const string path = @"D:\Music\A & B ""quoted"" <tag> 'single' - (Live).mp3";
        SongPlan plan = new() {
            Items = new List<PlanItem> {
                new PlanItem {
                    Path = path,
                    Artist = "A & B",
                    Title = "Title <tag>",
                    Comment = "\"Comment\"",
                },
            },
        };

        string xml = SaveToString(plan);

        Assert.IsTrue(xml.Contains("&amp;", StringComparison.Ordinal));
        Assert.IsTrue(xml.Contains("&quot;", StringComparison.Ordinal));
        Assert.IsTrue(xml.Contains("&lt;", StringComparison.Ordinal));
        Assert.IsTrue(xml.Contains("&gt;", StringComparison.Ordinal));

        SongPlan loaded = RoundTrip(plan);

        Assert.AreEqual(path, loaded.Items[0].Path);
        Assert.AreEqual("A & B", loaded.Items[0].Artist);
        Assert.AreEqual("Title <tag>", loaded.Items[0].Title);
        Assert.AreEqual("\"Comment\"", loaded.Items[0].Comment);
    }

    #endregion

    #region Loading

    /// <summary>
    /// Verifies that missing optional attributes are loaded as empty strings.
    /// </summary>
    [TestMethod]
    public void LoadsMissingOptionalAttributesAsEmpty() {
        string xml = $"""
            <?xml version="1.0" encoding="utf-8"?>
            <Plan version="{SongPlan.CurrentVersion}">
              <Format>TitleFirst</Format>
              <Items>
                <Item Path="C:\Music\C.mp3" Title="C" />
              </Items>
            </Plan>
            """;

        SongPlan plan = LoadFromString(xml);

        Assert.AreEqual(RenameFormat.TitleFirst, plan.Format);
        Assert.HasCount(1, plan.Items);
        Assert.AreEqual(@"C:\Music\C.mp3", plan.Items[0].Path);
        Assert.AreEqual(string.Empty, plan.Items[0].Artist);
        Assert.AreEqual("C", plan.Items[0].Title);
        Assert.AreEqual(string.Empty, plan.Items[0].Comment);
    }

    /// <summary>
    /// Verifies that a missing Items element leaves an empty initialized list.
    /// </summary>
    [TestMethod]
    public void LoadsMissingItemsAsEmptyList() {
        string xml = $"""
            <?xml version="1.0" encoding="utf-8"?>
            <Plan version="{SongPlan.CurrentVersion}">
              <Format>ArtistFirst</Format>
            </Plan>
            """;

        SongPlan plan = LoadFromString(xml);

        Assert.HasCount(0, plan.Items);
    }

    #endregion

    #region File access

    /// <summary>
    /// Verifies file save and load with spaces in the file path and UTF-8 output without a BOM.
    /// </summary>
    [TestMethod]
    public void SavesAndLoadsFileWithSpacesInPath() {
        string directory = Path.Combine(Path.GetTempPath(), $"SongTidy Plan Test {Guid.NewGuid():N}");
        string filePath = Path.Combine(directory, "plan with spaces.xml");
        Directory.CreateDirectory(directory);

        try {
            SongPlan plan = CreateSamplePlan();

            PlanXmlIO.Save(plan, filePath);

            Assert.IsTrue(File.Exists(filePath));

            byte[] bytes = File.ReadAllBytes(filePath);
            Assert.AreEqual((byte)'<', bytes[0]);

            string xml = Encoding.UTF8.GetString(bytes);
            Assert.IsTrue(
                xml.StartsWith("<?xml version=\"1.0\" encoding=\"utf-8\"?>", StringComparison.Ordinal),
                "The file should be written as UTF-8 without a BOM.");

            SongPlan loaded = PlanXmlIO.Load(filePath);
            Assert.AreEqual(plan.Format, loaded.Format);
            Assert.HasCount(plan.Items.Count, loaded.Items);
            AssertPlanItem(plan.Items[0], loaded.Items[0]);
        } finally {
            Directory.Delete(directory, recursive: true);
        }
    }

    #endregion

    /// <summary>
    /// Creates a sample plan containing two entries.
    /// </summary>
    /// <returns>The sample plan.</returns>
    private static SongPlan CreateSamplePlan() {
        return new SongPlan {
            Format = RenameFormat.ArtistFirst,
            Items = new List<PlanItem> {
                new PlanItem {
                    Path = @"D:\Music\A - B (Live).mp3",
                    Artist = "A",
                    Title = "B",
                    Comment = "Live",
                },
                new PlanItem {
                    Path = @"D:\Music\C.mp3",
                    Artist = string.Empty,
                    Title = "C",
                    Comment = string.Empty,
                },
            },
        };
    }

    /// <summary>
    /// Saves a plan to an in-memory stream and returns the decoded XML.
    /// </summary>
    /// <param name="plan">The plan to save.</param>
    /// <returns>The generated XML text.</returns>
    private static string SaveToString(SongPlan plan) {
        using MemoryStream stream = new();
        PlanXmlIO.Save(plan, stream);
        return Encoding.UTF8.GetString(stream.ToArray());
    }

    /// <summary>
    /// Loads a plan from XML text.
    /// </summary>
    /// <param name="xml">The XML text to load.</param>
    /// <returns>The loaded plan.</returns>
    private static SongPlan LoadFromString(string xml) {
        using MemoryStream stream = new(Encoding.UTF8.GetBytes(xml));
        return PlanXmlIO.Load(stream);
    }

    /// <summary>
    /// Saves and reloads a plan through an in-memory stream.
    /// </summary>
    /// <param name="plan">The plan to round-trip.</param>
    /// <returns>The reloaded plan.</returns>
    private static SongPlan RoundTrip(SongPlan plan) {
        using MemoryStream stream = new();
        PlanXmlIO.Save(plan, stream);
        stream.Position = 0;
        return PlanXmlIO.Load(stream);
    }

    /// <summary>
    /// Asserts that two plan items contain the same field values.
    /// </summary>
    /// <param name="expected">The expected item.</param>
    /// <param name="actual">The actual item.</param>
    private static void AssertPlanItem(PlanItem expected, PlanItem actual) {
        Assert.AreEqual(expected.Path, actual.Path);
        Assert.AreEqual(expected.Artist, actual.Artist);
        Assert.AreEqual(expected.Title, actual.Title);
        Assert.AreEqual(expected.Comment, actual.Comment);
    }
}