namespace dy.net.storage
{
    public static class SafeLocalMigrationFile
    {
        public static bool TryResolve(string path, IEnumerable<string> allowedRoots, out string fullPath, out string error)
        {
            fullPath = null;
            error = null;
            if (string.IsNullOrWhiteSpace(path))
            {
                error = "本地路径为空";
                return false;
            }

            try { fullPath = Path.GetFullPath(path); }
            catch (Exception ex)
            {
                error = "本地路径无效：" + ex.Message;
                return false;
            }

            var resolvedPath = fullPath;
            var root = (allowedRoots ?? Array.Empty<string>())
                .Select(Path.GetFullPath)
                .Where(candidate => IsWithin(resolvedPath, candidate))
                .OrderByDescending(x => x.Length)
                .FirstOrDefault();
            if (root == null)
            {
                error = "文件不在账号配置的旧存储根目录内";
                return false;
            }

            if (!File.Exists(fullPath))
            {
                error = "本地文件不存在";
                return false;
            }

            try
            {
                for (var current = fullPath; !string.IsNullOrWhiteSpace(current); current = Path.GetDirectoryName(current))
                {
                    FileSystemInfo info = File.Exists(current) ? new FileInfo(current) : new DirectoryInfo(current);
                    if (!string.IsNullOrWhiteSpace(info.LinkTarget))
                    {
                        error = "旧文件路径包含符号链接，已拒绝迁移";
                        return false;
                    }
                    if (string.Equals(current, root, StringComparison.Ordinal)) break;
                }
            }
            catch (Exception ex)
            {
                error = "无法验证旧文件路径：" + ex.Message;
                return false;
            }

            return true;
        }

        public static bool IsWithin(string candidate, string root)
        {
            var fullCandidate = Path.GetFullPath(candidate).TrimEnd(Path.DirectorySeparatorChar);
            var fullRoot = Path.GetFullPath(root).TrimEnd(Path.DirectorySeparatorChar);
            return string.Equals(fullCandidate, fullRoot, StringComparison.Ordinal)
                   || fullCandidate.StartsWith(fullRoot + Path.DirectorySeparatorChar, StringComparison.Ordinal);
        }
    }
}