// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

#nullable disable

using System.Security.Cryptography;
using System.Xml;
using Microsoft.Build.Framework;

namespace Microsoft.AspNetCore.StaticWebAssets.Tasks;

public class GenerateV1StaticWebAssetsManifest : Task
{
    private const string ContentRoot = "ContentRoot";
    private const string BasePath = "BasePath";
    private const string NodePath = "Path";
    private const string SourceId = "SourceId";

    [Required]
    public string TargetManifestPath { get; set; }

    [Required]
    public ITaskItem[] ContentRootDefinitions { get; set; }

    public override bool Execute()
    {
        if (!ValidateArguments())
        {
            return false;
        }

        return ExecuteCore();
    }

    private bool ExecuteCore()
    {
        var document = new XDocument(new XDeclaration("1.0", "utf-8", "yes"));
        var root = new XElement(
            "StaticWebAssets",
            new XAttribute("Version", "1.0"),
            CreateNodes());

        document.Add(root);

        var settings = new XmlWriterSettings
        {
            Encoding = Encoding.UTF8,
            CloseOutput = true,
            OmitXmlDeclaration = true,
            Indent = true,
            NewLineOnAttributes = false,
            Async = true
        };

        PersistManifest(document, settings);

        return !Log.HasLoggedErrors;
    }

    private void PersistManifest(XDocument document, XmlWriterSettings settings)
    {
        using var memory = new MemoryStream();
        using var xmlWriter = XmlWriter.Create(memory, settings);
        document.WriteTo(xmlWriter);
        xmlWriter.Flush();
        memory.Seek(0, SeekOrigin.Begin);
        var data = memory.ToArray();

#if !NET9_0_OR_GREATER
        using var sha256 = SHA256.Create();
        var currentHash = sha256.ComputeHash(data);
#else
        var currentHash = SHA256.HashData(data);
#endif
        var fileExists = File.Exists(TargetManifestPath);
        var existingManifestHash = fileExists ?
#if !NET9_0_OR_GREATER
            sha256.ComputeHash(File.ReadAllBytes(TargetManifestPath)) :
#else
            SHA256.HashData(File.ReadAllBytes(TargetManifestPath)) :
#endif
            [];

        if (!fileExists)
        {
            Log.LogMessage(MessageImportance.Low, $"Creating manifest because manifest file '{TargetManifestPath}' does not exist.");
            File.WriteAllBytes(TargetManifestPath, data);
        }
        else if (!currentHash.SequenceEqual(existingManifestHash))
        {
            Log.LogMessage(MessageImportance.Low, $"Updating manifest because manifest version '{Convert.ToBase64String(currentHash)}' is different from existing manifest hash '{Convert.ToBase64String(existingManifestHash)}'.");
            File.WriteAllBytes(TargetManifestPath, data);
        }
        else
        {
            Log.LogMessage(MessageImportance.Low, $"Skipping manifest updated because manifest version '{Convert.ToBase64String(currentHash)}' has not changed.");
        }
    }

    private IEnumerable<XElement> CreateNodes()
    {
        var nodes = new List<XElement>();
        for (var i = 0; i < ContentRootDefinitions.Length; i++)
        {
            var contentRootDefinition = ContentRootDefinitions[i];
            var basePath = contentRootDefinition.GetMetadata(BasePath);
            var contentRoot = contentRootDefinition.GetMetadata(ContentRoot);

            // basePath is meant to be a prefix for the files under contentRoot. MSbuild
            // normalizes '\' according to the OS, but this is going to be part of the url
            // so it needs to always be '/'.
            var normalizedBasePath = basePath.Replace("\\", "/");

            // contentRoot can have forward and trailing slashes and sometimes consecutive directory
            // separators. To be more flexible we will normalize the content root so that it contains a
            // single trailing separator.
            var normalizedContentRoot = $"{contentRoot.TrimEnd(Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar)}{Path.DirectorySeparatorChar}";

            // Here we simply skip additional items that have the same base path and same content root.
            if (!nodes.Exists(e => e.Attribute("BasePath").Value.Equals(normalizedBasePath, StringComparison.OrdinalIgnoreCase) &&
                e.Attribute("Path").Value.Equals(normalizedContentRoot, StringComparison.OrdinalIgnoreCase)))
            {
                nodes.Add(new XElement("ContentRoot",
                    new XAttribute("BasePath", normalizedBasePath),
                    new XAttribute("Path", normalizedContentRoot)));
            }
        }

        // Its important that we order the nodes here to produce a manifest deterministically.
        return nodes.OrderBy(e => e.Attribute(BasePath).Value).ThenBy(e => e.Attribute(NodePath).Value);
    }

    private bool ValidateArguments()
    {
        for (var i = 0; i < ContentRootDefinitions.Length; i++)
        {
            var contentRootDefinition = ContentRootDefinitions[i];
            if (!EnsureRequiredMetadata(contentRootDefinition, BasePath) ||
                !EnsureRequiredMetadata(contentRootDefinition, ContentRoot) ||
                !EnsureRequiredMetadata(contentRootDefinition, SourceId))
            {
                return false;
            }
        }

        return true;
    }

    private bool EnsureRequiredMetadata(ITaskItem item, string metadataName)
    {
        var value = item.GetMetadata(metadataName);
        if (string.IsNullOrEmpty(value))
        {
            Log.LogError($"Missing required metadata '{metadataName}' for '{item.ItemSpec}'.");
            return false;
        }

        return true;
    }
}