using System;
using System.IO;

namespace X86Disassembler.PE.Parsers
{
    /// <summary>
    /// Parser for the DOS header of a PE file
    /// </summary>
    public class DOSHeaderParser : IParser<DOSHeader>
    {
        // DOS Header constants
        private const ushort DOS_SIGNATURE = 0x5A4D;       // 'MZ'
        
        /// <summary>
        /// Parse the DOS header from the binary reader
        /// </summary>
        /// <param name="reader">The binary reader positioned at the start of the DOS header</param>
        /// <returns>The parsed DOS header</returns>
        public DOSHeader Parse(BinaryReader reader)
        {
            DOSHeader header = new DOSHeader();
            
            header.e_magic = reader.ReadUInt16();
            if (header.e_magic != DOS_SIGNATURE)
            {
                throw new InvalidDataException("Invalid DOS signature (MZ)");
            }
            
            header.e_cblp = reader.ReadUInt16();
            header.e_cp = reader.ReadUInt16();
            header.e_crlc = reader.ReadUInt16();
            header.e_cparhdr = reader.ReadUInt16();
            header.e_minalloc = reader.ReadUInt16();
            header.e_maxalloc = reader.ReadUInt16();
            header.e_ss = reader.ReadUInt16();
            header.e_sp = reader.ReadUInt16();
            header.e_csum = reader.ReadUInt16();
            header.e_ip = reader.ReadUInt16();
            header.e_cs = reader.ReadUInt16();
            header.e_lfarlc = reader.ReadUInt16();
            header.e_ovno = reader.ReadUInt16();
            
            header.e_res = new ushort[4];
            for (int i = 0; i < 4; i++)
            {
                header.e_res[i] = reader.ReadUInt16();
            }
            
            header.e_oemid = reader.ReadUInt16();
            header.e_oeminfo = reader.ReadUInt16();
            
            header.e_res2 = new ushort[10];
            for (int i = 0; i < 10; i++)
            {
                header.e_res2[i] = reader.ReadUInt16();
            }
            
            header.e_lfanew = reader.ReadUInt32();
            
            return header;
        }
    }
}