namespace Agent.Windows.Security;

[Flags]
public enum FileCapability { None = 0, Read = 1, Write = 2, Execute = 4, Delete = 8 }

public sealed record FilePolicyEntry(string Path, FileCapability Capabilities, string Origin = "unspecified");

public sealed class PathPolicy(IEnumerable<FilePolicyEntry> entries)
{
    private readonly IReadOnlyList<FilePolicyEntry> _entries = entries.Select(entry => entry with { Path = ResolvedPath.Resolve(entry.Path, requireExisting: false) }).ToArray();

    public bool IsAllowed(string path, FileCapability required)
    {
        string canonical = ResolvedPath.Resolve(path, requireExisting: required is FileCapability.Read or FileCapability.Execute or FileCapability.Delete);
        return _entries.Any(entry => IsAtOrBelow(canonical, entry.Path) && (entry.Capabilities & required) == required);
    }

    public void Demand(string path, FileCapability required)
    {
        if (!IsAllowed(path, required))
            throw new SandboxPolicyException("policy.deny", $"Resolved Path '{path}' is outside the Effective Sandbox Policy for {required}.",
                "filesystem", Path.GetFullPath(path), required.ToString().ToLowerInvariant(), "Confirm a Workspace or Mount that grants the required Filesystem Capability, then restart the server.");
    }

    private static bool IsAtOrBelow(string candidate, string root) =>
        candidate.Equals(root, StringComparison.OrdinalIgnoreCase) ||
        candidate.StartsWith(root.TrimEnd(Path.DirectorySeparatorChar) + Path.DirectorySeparatorChar, StringComparison.OrdinalIgnoreCase);
}

public static class ResolvedPath
{
    public static string Resolve(string path, bool requireExisting = true)
    {
        if (string.IsNullOrWhiteSpace(path)) throw new SandboxPolicyException("path.invalid", "Path is required.");
        string fullPath = Path.GetFullPath(path);
        string? root = Path.GetPathRoot(fullPath);
        if (string.IsNullOrEmpty(root)) throw new SandboxPolicyException("path.invalid", "Path has no filesystem root.");
        if (root.StartsWith("\\\\", StringComparison.Ordinal))
            throw new SandboxPolicyException("path.non_local", "Only local filesystem paths are supported.", "filesystem", fullPath, null, "Select a local Workspace, Mount, Runtime Root, or Executable.");
        string current = root;
        var visited = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        foreach (string segment in fullPath[root.Length..].Split(Path.DirectorySeparatorChar, StringSplitOptions.RemoveEmptyEntries))
        {
            current = Path.Combine(current, segment);
            if (!File.Exists(current) && !Directory.Exists(current)) continue;
            while ((File.GetAttributes(current) & FileAttributes.ReparsePoint) != 0)
            {
                string reparsePath = Path.GetFullPath(current);
                if (!visited.Add(reparsePath))
                    throw new SandboxPolicyException("path.reparse_cycle", $"Reparse resolution cycle detected at '{reparsePath}'.", "filesystem", reparsePath, null, "Remove the reparse cycle.");
                FileSystemInfo info = Directory.Exists(current) ? new DirectoryInfo(current) : new FileInfo(current);
                string? target;
                try { target = info.ResolveLinkTarget(returnFinalTarget: false)?.FullName; }
                catch (IOException ex)
                {
                    throw new SandboxPolicyException("path.reparse_unresolved", $"Could not resolve reparse component '{current}': {ex.Message}",
                        "filesystem", current, null, "Repair or remove the reparse point.");
                }
                if (string.IsNullOrWhiteSpace(target))
                    throw new SandboxPolicyException("path.reparse_unresolved", $"Could not resolve reparse component '{current}'.", "filesystem", current, null, "Repair or remove the reparse point.");
                current = Path.GetFullPath(target);
            }
        }
        if (requireExisting && !File.Exists(current) && !Directory.Exists(current)) throw new FileNotFoundException("Resolved Path does not exist.", current);
        return Path.TrimEndingDirectorySeparator(current);
    }
}

public sealed class SandboxPolicyException(string code, string message, string category = "policy", string? targetPath = null,
    string? requiredPermission = null, string? resolution = null) : UnauthorizedAccessException(message)
{
    public string Code { get; } = code;
    public string Category { get; } = category;
    public string? TargetPath { get; } = targetPath;
    public string? RequiredPermission { get; } = requiredPermission;
    public string? Resolution { get; } = resolution;
}