// /***************************************************************************
// The Disc Image Chef
// ----------------------------------------------------------------------------
//
// Filename       : Apple2.cs
// Author(s)      : Natalia Portillo <claunia@claunia.com>
//
// Component      : Device structures decoders.
//
// --[ Description ] ----------------------------------------------------------
//
//     Decodes Apple ][ floppy structures.
//
// --[ 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 © 2011-2016 Natalia Portillo
// ****************************************************************************/

using System.Runtime.InteropServices;

namespace DiscImageChef.Decoders.Floppy
{
    /// <summary>
    /// Methods and structures for Apple ][ floppy decoding
    /// </summary>
    public static class Apple2
    {
        /// <summary>
        /// GCR-encoded Apple ][ GCR floppy track
        /// </summary>
        public struct RawTrack
        {
            /// <summary>
            /// Track preamble, set to self-sync 0xFF, between 40 and 95 bytes
            /// </summary>
            public byte[] gap;
            public RawSector[] sectors;
        }

        /// <summary>
        /// GCR-encoded Apple ][ GCR floppy sector
        /// </summary>
        public struct RawSector
        {
            /// <summary>
            /// Address field
            /// </summary>
            public RawDataField addressField;
            /// <summary>
            /// Track preamble, set to self-sync 0xFF, between 5 and 10 bytes
            /// </summary>
            public byte[] innerGap;
            /// <summary>
            /// Data field
            /// </summary>
            public RawDataField dataField;
            /// <summary>
            /// Track preamble, set to self-sync 0xFF, between 14 and 24 bytes
            /// </summary>
            public byte[] gap;
        }

        /// <summary>
        /// GCR-encoded Apple ][ GCR floppy sector address field
        /// </summary>
        public struct RawAddressField
        {
            /// <summary>
            /// Always 0xD5, 0xAA, 0x96
            /// </summary>
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 3)]
            public byte[] prologue;
            /// <summary>
            /// Volume number encoded as:
            /// volume[0] = (decodedVolume >> 1) | 0xAA
            /// volume[1] = decodedVolume | 0xAA
            /// </summary>
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)]
            public byte[] volume;
            /// <summary>
            /// Track number encoded as:
            /// track[0] = (decodedTrack >> 1) | 0xAA
            /// track[1] = decodedTrack | 0xAA
            /// </summary>
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)]
            public byte[] track;
            /// <summary>
            /// Sector number encoded as:
            /// sector[0] = (decodedSector >> 1) | 0xAA
            /// sector[1] = decodedSector | 0xAA
            /// </summary>
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)]
            public byte[] sector;
            /// <summary>
            /// decodedChecksum = decodedVolume ^ decodedTrack ^ decodedSector
            /// checksum[0] = (decodedChecksum >> 1) | 0xAA
            /// checksum[1] = decodedChecksum | 0xAA
            /// </summary>
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)]
            public byte[] checksum;
            /// <summary>
            /// Always 0xDE, 0xAA, 0xEB
            /// </summary>
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 3)]
            public byte[] epilogue;
        }

        /// <summary>
        /// GCR-encoded Apple ][ GCR floppy sector data field
        /// </summary>
        public struct RawDataField
        {
            /// <summary>
            /// Always 0xD5, 0xAA, 0xAD
            /// </summary>
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 3)]
            public byte[] prologue;
            /// <summary>
            /// Encoded data bytes.
            /// 410 bytes for 5to3 (aka DOS 3.2) format
            /// 342 bytes for 6to2 (aka DOS 3.3) format
            /// </summary>
            public byte[] data;
            public byte checksum;
            /// <summary>
            /// Always 0xDE, 0xAA, 0xEB
            /// </summary>
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 3)]
            public byte[] epilogue;
        }
    }
}

