// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System;
 
internal static partial class Interop
{
    internal static partial class @procfs
    {
        internal ref struct ParsedMount
        {
            public required ReadOnlySpan<char> Root { get; init; }
            public required ReadOnlySpan<char> MountPoint { get; init; }
            public required ReadOnlySpan<char> FileSystemType { get; init; }
            public required ReadOnlySpan<char> SuperOptions { get; init; }
        }
 
        internal static bool TryParseMountInfoLine(ReadOnlySpan<char> line, out ParsedMount result)
        {
            result = default;
 
            // See man page for /proc/[pid]/mountinfo for details, e.g.:
            //     (1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
            //     36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
            // but (7) is optional and could exist as multiple fields; the (8) separator marks
            // the end of the optional values.
 
            MemoryExtensions.SpanSplitEnumerator<char> fields = line.Split(' ');
 
            // (1) mount ID
            // (2) parent ID
            // (3) major:minor
            if (!fields.MoveNext() || !fields.MoveNext() || !fields.MoveNext())
            {
                return false;
            }
 
            // (4) root
            if (!fields.MoveNext())
            {
                return false;
            }
            ReadOnlySpan<char> root = line[fields.Current];
 
            // (5) mount point
            if (!fields.MoveNext())
            {
                return false;
            }
            ReadOnlySpan<char> mountPoint = line[fields.Current];
 
            // (8) separator
            const string Separator = " - ";
            int endOfOptionalFields = line.IndexOf(Separator, StringComparison.Ordinal);
            if (endOfOptionalFields == -1)
            {
                return false;
            }
            line = line.Slice(endOfOptionalFields + Separator.Length);
            fields = line.Split(' ');
 
            // (9) filesystem type
            if (!fields.MoveNext())
            {
                return false;
            }
            ReadOnlySpan<char> fileSystemType = line[fields.Current];
 
            // (10) mount source
            if (!fields.MoveNext())
            {
                return false;
            }
 
            // (11) super options
            if (!fields.MoveNext())
            {
                return false;
            }
            ReadOnlySpan<char> superOptions = line[fields.Current];
 
            result = new ParsedMount()
            {
                Root = root,
                MountPoint = mountPoint,
                FileSystemType = fileSystemType,
                SuperOptions = superOptions
            };
            return true;
        }
    }
}