using System.Runtime.InteropServices;

namespace BinaryObjectScanner.Models.PortableExecutable
{
    /// <summary>
    /// Each row of the section table is, in effect, a section header. This table
    /// immediately follows the optional header, if any. This positioning is required
    /// because the file header does not contain a direct pointer to the section table.
    /// Instead, the location of the section table is determined by calculating the
    /// location of the first byte after the headers. Make sure to use the size of
    /// the optional header as specified in the file header.
    /// 
    /// The number of entries in the section table is given by the NumberOfSections
    /// field in the file header. Entries in the section table are numbered starting
    /// from one (1). The code and data memory section entries are in the order chosen
    /// by the linker.
    /// 
    /// In an image file, the VAs for sections must be assigned by the linker so that
    /// they are in ascending order and adjacent, and they must be a multiple of the
    /// SectionAlignment value in the optional header.
    /// </summary>
    /// <see href="https://learn.microsoft.com/en-us/windows/win32/debug/pe-format"/>
    [StructLayout(LayoutKind.Sequential)]
    public sealed class SectionHeader
    {
        /// <summary>
        /// An 8-byte, null-padded UTF-8 encoded string. If the string is exactly 8
        /// characters long, there is no terminating null. For longer names, this field
        /// contains a slash (/) that is followed by an ASCII representation of a
        /// decimal number that is an offset into the string table. Executable images
        /// do not use a string table and do not support section names longer than 8
        /// characters. Long names in object files are truncated if they are emitted
        /// to an executable file. 
        /// </summary>
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 8)]
        public byte[] Name;

        /// <summary>
        /// The total size of the section when loaded into memory. If this value is
        /// greater than SizeOfRawData, the section is zero-padded. This field is valid
        /// only for executable images and should be set to zero for object files.
        /// </summary>
        public uint VirtualSize;

        /// <summary>
        /// For executable images, the address of the first byte of the section relative
        /// to the image base when the section is loaded into memory. For object files,
        /// this field is the address of the first byte before relocation is applied;
        /// for simplicity, compilers should set this to zero. Otherwise, it is an
        /// arbitrary value that is subtracted from offsets during relocation.
        /// </summary>
        public uint VirtualAddress;

        /// <summary>
        /// The size of the section (for object files) or the size of the initialized
        /// data on disk (for image files). For executable images, this must be a multiple
        /// of FileAlignment from the optional header. If this is less than VirtualSize,
        /// the remainder of the section is zero-filled. Because the SizeOfRawData field
        /// is rounded but the VirtualSize field is not, it is possible for SizeOfRawData
        /// to be greater than VirtualSize as well. When a section contains only
        /// uninitialized data, this field should be zero.
        /// </summary>
        public uint SizeOfRawData;

        /// <summary>
        /// The file pointer to the first page of the section within the COFF file. For
        /// executable images, this must be a multiple of FileAlignment from the optional
        /// header. For object files, the value should be aligned on a 4-byte boundary
        /// for best performance. When a section contains only uninitialized data, this
        /// field should be zero.
        /// </summary>
        public uint PointerToRawData;

        /// <summary>
        /// The file pointer to the beginning of relocation entries for the section. This
        /// is set to zero for executable images or if there are no relocations.
        /// </summary>
        public uint PointerToRelocations;

        /// <summary>
        /// The file pointer to the beginning of line-number entries for the section. This
        /// is set to zero if there are no COFF line numbers. This value should be zero for
        /// an image because COFF debugging information is deprecated. 
        /// </summary>
        public uint PointerToLinenumbers;

        /// <summary>
        /// The number of relocation entries for the section. This is set to zero for
        /// executable images.
        /// </summary>
        public ushort NumberOfRelocations;

        /// <summary>
        /// The number of line-number entries for the section. This value should be zero
        /// for an image because COFF debugging information is deprecated.
        /// </summary>
        public ushort NumberOfLinenumbers;

        /// <summary>
        /// The flags that describe the characteristics of the section.
        /// </summary>
        public SectionFlags Characteristics;

        /// <summary>
        /// COFF Relocations (Object Only)
        /// </summary>
        public COFFRelocation[] COFFRelocations;

        /// <summary>
        /// COFF Line Numbers (Deprecated)
        /// </summary>
        public COFFLineNumber[] COFFLineNumbers;
    }
}