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

using System;
using System.Collections.Generic;
using System.IO;
using System.Runtime.CompilerServices;
using System.Runtime.ExceptionServices;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.Marshalling;

internal static partial class Interop
{
    internal static partial class Sys
    {
        [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_GetAllMountPoints")]
        private static unsafe partial int GetAllMountPoints(delegate* unmanaged<void*, byte*, void> onFound, void* context);

        private struct AllMountPointsContext
        {
            internal List<string> _results;
            internal ExceptionDispatchInfo? _exception;
        }

        [UnmanagedCallersOnly]
        private static unsafe void AddMountPoint(void* context, byte* name)
        {
            AllMountPointsContext* callbackContext = (AllMountPointsContext*)context;
            try
            {
                callbackContext->_results.Add(Utf8StringMarshaller.ConvertToManaged(name)!);
            }
            catch (Exception e)
            {
                callbackContext->_exception = ExceptionDispatchInfo.Capture(e);
            }
        }

        internal static string[] GetAllMountPoints()
        {
            // Prefer using proc mountinfo as the mount point paths are relative to the process's root.
            if (OperatingSystem.IsLinux())
            {
                if (File.Exists(Interop.procfs.ProcMountInfoFilePath))
                {
                    List<string> mountPoints = new();

                    using StreamReader reader = new(Interop.procfs.ProcMountInfoFilePath);

                    string? line;
                    while ((line = reader.ReadLine()) is not null)
                    {
                        if (Interop.procfs.TryParseMountInfoLine(line, out Interop.procfs.ParsedMount mount))
                        {
                            mountPoints.Add(mount.MountPoint.ToString());
                        }
                    }

                    return mountPoints.ToArray();
                }
            }

            AllMountPointsContext context = default;
            context._results = new List<string>();

            unsafe
            {
                GetAllMountPoints(&AddMountPoint, &context);
            }

            context._exception?.Throw();

            return context._results.ToArray();
        }
    }
}