namespace MrGameEng.Mods;

/// <summary>A file contributed by a mod, addressed by its content-relative path.</summary>
/// <param name="RelativePath">Path relative to the content folder, forward slashes.</param>
/// <param name="FullPath">Absolute path of the winning file on disk.</param>
/// <param name="Mod">The mod that contributed the file.</param>
public readonly record struct ModFile(string RelativePath, string FullPath, Mod Mod);

/// <summary>
/// Merged view of one content folder (e.g. <c>Textures</c>) across the active mods in load
/// order: a later mod shipping a file under the same relative path overrides the earlier
/// one. Paths use forward slashes and match case-insensitively (Windows-friendly content).
/// </summary>
public sealed class ModContentTree
{
    private readonly Dictionary<string, ModFile> _files;

    private ModContentTree(Dictionary<string, ModFile> files, IReadOnlyList<ModFile> ordered)
    {
        _files = files;
        Files = ordered;
    }

    /// <summary>Winning files, sorted by relative path — deterministic for identical mod sets.</summary>
    public IReadOnlyList<ModFile> Files { get; }

    /// <summary>Returns the winning file for <paramref name="relativePath"/>.</summary>
    public bool TryGet(string relativePath, out ModFile file) =>
        _files.TryGetValue(Normalize(relativePath), out file);

    /// <summary>
    /// Builds the merged tree of <paramref name="contentFolder"/> over <paramref name="mods"/>
    /// (in load order). With <paramref name="extensions"/> only matching files are included
    /// (e.g. <c>".png"</c>); without them, every file.
    /// </summary>
    public static ModContentTree Build(IReadOnlyList<Mod> mods, string contentFolder, params string[] extensions)
    {
        var files = new Dictionary<string, ModFile>(StringComparer.OrdinalIgnoreCase);
        foreach (var mod in mods)
        {
            var root = mod.ContentPath(contentFolder);
            if (!Directory.Exists(root))
            {
                continue;
            }

            foreach (var fullPath in Directory.EnumerateFiles(root, "*", SearchOption.AllDirectories))
            {
                if (extensions.Length > 0 &&
                    !extensions.Contains(Path.GetExtension(fullPath), StringComparer.OrdinalIgnoreCase))
                {
                    continue;
                }

                var relative = Normalize(Path.GetRelativePath(root, fullPath));
                files[relative] = new ModFile(relative, fullPath, mod); // поздний мод побеждает
            }
        }

        var ordered = files.Values.OrderBy(f => f.RelativePath, StringComparer.Ordinal).ToList();
        return new ModContentTree(files, ordered);
    }

    private static string Normalize(string path) => path.Replace('\\', '/');
}