// /***************************************************************************
// Aaru Data Preservation Suite
// ----------------------------------------------------------------------------
//
// Filename       : Structs.cs
// Author(s)      : Michael Drüing <michael@drueing.de>
//
// Component      : Disk image plugins.
//
// --[ Description ] ----------------------------------------------------------
//
//     Contains structures for d2f disk images.
//
// --[ License ] --------------------------------------------------------------
//
//     This library is free software; you can redistribute it and/or modify
//     it under the terms of the GNU Lesser General Public License as
//     published by the Free Software Foundation; either version 2.1 of the
//     License, or (at your option) any later version.
//
//     This library is distributed in the hope that it will be useful, but
//     WITHOUT ANY WARRANTY; without even the implied warranty of
//     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
//     Lesser General Public License for more details.
//
//     You should have received a copy of the GNU Lesser General Public
//     License along with this library; if not, see <http://www.gnu.org/licenses/>.
//
// ----------------------------------------------------------------------------
// Copyright © 2018-2019 Michael Drüing
// Copyright © 2011-2022 Natalia Portillo
// ****************************************************************************/

using System.Runtime.InteropServices;

namespace Aaru.DiscImages;

public sealed partial class WCDiskImage
{
    /// <summary>The expected signature of a proper image file.</summary>
    const string FILE_SIGNATURE = "WC DISK IMAGE\x1a\x1a";

    /// <summary>The global header of a WCDiskImage file</summary>
    [StructLayout(LayoutKind.Sequential, Pack = 1)]
    readonly struct FileHeader
    {
        /// <summary>The signature should be "WC DISK IMAGE\0x1a\0x1a\0x00"</summary>
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
        public readonly byte[] signature;

        /// <summary>Version (currently only version 0 and 1 is known)</summary>
        public readonly byte version;

        /// <summary>The number of heads. Only 1 or 2 is supported</summary>
        public readonly byte heads;

        /// <summary>Sectors per track, maximum is 18</summary>
        public readonly byte sectorsPerTrack;

        /// <summary>The number of tracks/cylinders. 80 is the maximum</summary>
        public readonly byte cylinders;

        /// <summary>
        ///     The "extra tracks" that are present. What this means is that the tracks 81 and 82 might contain data (on an
        ///     80-track disk) and that this data was dumped too. The order is head0extra1, head1extra1, head0extra2, head1extra2.
        ///     1 means track is present.
        /// </summary>
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
        public readonly byte[] extraTracks;

        /// <summary>Additional metadata present flags.</summary>
        public readonly ExtraFlag extraFlags;

        /// <summary>Padding to make the header 32 bytes.</summary>
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 7)]
        public readonly byte[] reserved;
    }

    enum ExtraFlag : byte
    {
        /// <summary>Set if a Comment is present after the image</summary>
        Comment = 0x01,

        /// <summary>Set if a directory listing is present after the image</summary>
        Directory = 0x02
    }

    /// <summary>The Sector header that precedes each sector</summary>
    [StructLayout(LayoutKind.Sequential, Pack = 1)]
    readonly struct SectorHeader
    {
        /// <summary>The sector flag (i.e. type)</summary>
        public readonly SectorFlag flag;

        /// <summary>The head this sector belongs to.</summary>
        public readonly byte head;

        /// <summary>The sector number within the track. Must be consecutive.</summary>
        public readonly byte sector;

        /// <summary>The cylinder number this sector belongs to.</summary>
        public readonly byte cylinder;

        /// <summary>A simple CRC16 over the data, to detect errors.</summary>
        public readonly short crc;
    }

    enum SectorFlag : byte
    {
        /// <summary>A normal sector</summary>
        Normal = 0x00,

        /// <summary>A bad sector that could not be read</summary>
        BadSector = 0x01,

        /// <summary>A sector filled with a repeating byte value. The value is encoded in the LSB of the <c>crc</c> field.</summary>
        RepeatByte = 0x02,

        /// <summary>
        ///     Not a sector but a comment. Must come after all user data. The <c>crc</c> field is the length of the comment
        ///     data.
        /// </summary>
        Comment = 0x03,

        /// <summary>Not a sector but the directory information. The <c>crc</c> field is the length of the data.</summary>
        Directory = 0x04
    }
}