using System;
using System.Collections.Generic;

namespace X86Disassembler.PE
{
    /// <summary>
    /// Utility class for PE format operations
    /// </summary>
    public class PEUtility
    {
        private readonly List<SectionHeader> _sectionHeaders;
        private readonly uint _sizeOfHeaders;
        
        /// <summary>
        /// Initialize a new instance of the PEUtility class
        /// </summary>
        /// <param name="sectionHeaders">The section headers</param>
        /// <param name="sizeOfHeaders">The size of the headers</param>
        public PEUtility(List<SectionHeader> sectionHeaders, uint sizeOfHeaders)
        {
            _sectionHeaders = sectionHeaders;
            _sizeOfHeaders = sizeOfHeaders;
        }
        
        /// <summary>
        /// Converts a Relative Virtual Address (RVA) to a file offset
        /// </summary>
        /// <param name="rva">The RVA to convert</param>
        /// <returns>The corresponding file offset</returns>
        public uint RvaToOffset(uint rva)
        {
            if (rva == 0)
            {
                return 0;
            }
            
            foreach (var section in _sectionHeaders)
            {
                // Check if the RVA is within this section
                if (rva >= section.VirtualAddress && rva < section.VirtualAddress + section.VirtualSize)
                {
                    // Calculate the offset within the section
                    uint offsetInSection = rva - section.VirtualAddress;
                    
                    // Make sure we don't exceed the raw data size
                    if (offsetInSection < section.SizeOfRawData)
                    {
                        return section.PointerToRawData + offsetInSection;
                    }
                }
            }
            
            // If the RVA is not within any section, it might be in the headers
            if (rva < _sizeOfHeaders)
            {
                return rva;
            }
            
            throw new ArgumentException($"RVA {rva:X8} is not within any section");
        }
    }
}