namespace Explorer.Domain;

public static class PathRules
{
    public const string ExtendedPrefix = @"\\?\";
    public const string ExtendedUncPrefix = @"\\?\UNC\";

    public static string ToExtended(string path)
    {
        if (string.IsNullOrWhiteSpace(path))
        {
            return path;
        }

        if (path.StartsWith(ExtendedPrefix, StringComparison.Ordinal))
        {
            return path;
        }

        if (path.StartsWith(@"\\", StringComparison.Ordinal))
        {
            return ExtendedUncPrefix + path[2..];
        }

        return ExtendedPrefix + path;
    }

    public static string FromExtended(string path)
    {
        if (path.StartsWith(ExtendedUncPrefix, StringComparison.OrdinalIgnoreCase))
        {
            return @"\\" + path[ExtendedUncPrefix.Length..];
        }

        if (path.StartsWith(ExtendedPrefix, StringComparison.Ordinal))
        {
            return path[ExtendedPrefix.Length..];
        }

        return path;
    }

    public static bool IsUnc(string path)
    {
        var p = FromExtended(path);
        return p.StartsWith(@"\\", StringComparison.Ordinal);
    }

    public static string NormalizeDirectorySeparators(string path)
        => path.Replace('/', '\\');

    public static string Combine(string root, string relative)
    {
        root = FromExtended(root).TrimEnd('\\');
        relative = relative.Replace('/', '\\').TrimStart('\\');
        if (string.IsNullOrEmpty(relative))
        {
            return EnsureDirectoryTrailingSlashIfRoot(root);
        }

        return root + "\\" + relative;
    }

    public static string MakeRelative(string root, string fullPath)
    {
        var r = FromExtended(root).TrimEnd('\\');
        var f = FromExtended(fullPath).TrimEnd('\\');
        if (f.Equals(r, StringComparison.OrdinalIgnoreCase))
        {
            return string.Empty;
        }

        if (f.StartsWith(r + "\\", StringComparison.OrdinalIgnoreCase))
        {
            return f[(r.Length + 1)..];
        }

        return f;
    }

    public static string CanonicalUncRoot(string path)
    {
        var p = FromExtended(path).TrimEnd('\\');
        if (!p.StartsWith(@"\\", StringComparison.Ordinal))
        {
            return p;
        }

        var parts = p[2..].Split('\\', StringSplitOptions.RemoveEmptyEntries);
        if (parts.Length < 2)
        {
            return @"\\" + p[2..].ToLowerInvariant();
        }

        return @"\\" + parts[0].ToLowerInvariant() + "\\" + parts[1];
    }

    public static string Parent(string path)
    {
        var p = FromExtended(path).TrimEnd('\\');
        if (p.Length >= 2 && p[1] == ':' && p.Length <= 3)
        {
            return p.Length == 2 ? p + "\\" : p + (p.EndsWith('\\') ? "" : "\\");
        }

        if (IsUnc(p))
        {
            var root = CanonicalUncRoot(p);
            if (p.Equals(root, StringComparison.OrdinalIgnoreCase))
            {
                return root;
            }
        }

        var idx = p.LastIndexOf('\\');
        if (idx <= 0)
        {
            return p;
        }

        if (idx == 2 && p[1] == ':')
        {
            return p[..3];
        }

        return p[..idx];
    }

    public static bool IsDriveRoot(string path)
    {
        var p = FromExtended(path).TrimEnd('\\');
        return p.Length == 2 && p[1] == ':';
    }

    public static string EnsureDirectoryTrailingSlashIfRoot(string path)
    {
        var p = FromExtended(path);
        if (p.Length == 2 && p[1] == ':')
        {
            return p + "\\";
        }

        return p;
    }

    public static string GetFileName(string path)
    {
        var p = FromExtended(path).TrimEnd('\\');
        var idx = p.LastIndexOf('\\');
        return idx < 0 ? p : p[(idx + 1)..];
    }

    public static string RelativeParent(string pathRel)
    {
        if (string.IsNullOrEmpty(pathRel))
        {
            return string.Empty;
        }

        var n = NormalizeDirectorySeparators(pathRel).TrimEnd('\\');
        var idx = n.LastIndexOf('\\');
        return idx < 0 ? string.Empty : n[..idx];
    }

    public static string JoinDisplay(string? root, string pathRel)
    {
        if (string.IsNullOrWhiteSpace(root))
        {
            return pathRel;
        }

        return string.IsNullOrWhiteSpace(pathRel) ? EnsureDirectoryTrailingSlashIfRoot(root) : Combine(root, pathRel);
    }

    public static string ShortenDisplay(string path, int maxChars = 64)
    {
        var p = FromExtended(path);
        if (p.Length <= maxChars)
        {
            return p;
        }

        var unc = IsUnc(p);
        var parts = p.TrimEnd('\\').Split('\\', StringSplitOptions.RemoveEmptyEntries);
        if (parts.Length <= 2)
        {
            return p;
        }

        string prefix;
        var start = 0;
        if (unc)
        {
            prefix = @"\\" + parts[0] + "\\" + parts[1];
            start = 2;
        }
        else
        {
            prefix = parts.Length > 2 ? parts[0] + "\\" + parts[1] : parts[0];
            start = parts.Length > 2 ? 2 : 1;
        }

        var leaf = parts[^1];
        var parent = parts.Length - 1 > start ? parts[^2] + "\\" + leaf : leaf;
        var candidate = prefix + @"\…\" + parent;
        if (candidate.Length <= maxChars)
        {
            return candidate;
        }

        candidate = prefix + @"\…\" + leaf;
        return candidate.Length <= maxChars ? candidate : prefix + @"\…";
    }
}