// Intel assembly language


// segments: code, stack

#include "minicc.h"

#include <algorithm>
#include <array>
#include <deque>
#include <functional>
#include <stdexcept>
#include <functional>
#include <stdexcept>
#include <string>
#include <unordered_map>
#include <vector>

using namespace std::string_literals;
using namespace std::placeholders;

namespace {

 // binary code operators
 std::vector<uint8_t> operator+(std::vector<uint8_t> a, const std::vector<uint8_t>& b) {
  a.insert(a.end(), b.begin(), b.end());
  return a;
 }

 std::vector<uint8_t> operator+(std::vector<uint8_t> a, const uint8_t& b) {
  a.push_back(b);
  return a;
 }

 // REX prefix: 0b0100WRXB
 std::vector<uint8_t> REX(std::string s) {
  uint8_t result{0b01000000};
  if (s == "W")
   result |= 0b00001000;
  if (s == "R")
   result |= 0b00000100;
  if (s == "X")
   result |= 0b00000010;
  if (s == "B")
   result |= 0b00000001;

  return { result }; 
 }

 std::vector<uint8_t> imm8(std::string s) {
  long value{ std::stol(s) };
  uint8_t* bin = reinterpret_cast<uint8_t*>(&value);
  return { uint8_t(*bin & 0xFF) };
 }

 std::vector<uint8_t> imm32(std::string s) {
  long value{ std::stol(s) };
  uint32_t* bin = reinterpret_cast<uint32_t*>(&value);
  return {uint8_t(*bin & 0xFF), uint8_t(*bin >> 8 & 0xFF), uint8_t(*bin >> 16 & 0xFF), uint8_t(*bin >> 24 & 0xFF) };
 }

 std::unordered_map<std::string, size_t> IndexOfRegister{
  {"al", 0}, {"ah", 4},
  {"bl", 3}, {"bh", 7},
  {"cl", 1}, {"ch", 5},
  {"dl", 2}, {"dh", 6},

  {"ax", 0}, {"sp", 4},
  {"bx", 3}, {"bp", 7},
  {"cx", 1}, {"si", 5},
  {"dx", 2}, {"di", 6},

  {"eax", 0}, {"esp", 4},
  {"ebx", 3}, {"ebp", 7},
  {"ecx", 1}, {"esi", 5},
  {"edx", 2}, {"edi", 6},
 };

 // Manual, page 530
 // Reg + Reg/Memory
 uint8_t ModRM(std::string reg, std::string rm) {
  // TODO: extend
  uint8_t result{0b11000000};

  auto index1{ IndexOfRegister.find(reg) };
  if (index1 == IndexOfRegister.end())
   throw std::runtime_error("Unknown register for arg1: "s + reg);

  result |= (index1->second << 3);

  auto index2{ IndexOfRegister.find(rm) };
  if (index2 == IndexOfRegister.end())
   throw std::runtime_error("Unknown register for arg2: "s + rm);

  result |= index2->second;

  return result;
 }

 enum class AddressType {
  Relative8,
  Relative16,
  Relative32,
  Absolute8,
  Absolute16,
  Absolute32,
 };

 struct Address
 {
  AddressType type;
  size_t position; // relative to respective machine code, e.g. byte 1 in jump
  std::string label; // where to jump to, as label
 };

 struct InstructionCode
 {
  std::vector<uint8_t> machine_code;
  std::vector<Address> addresses;
 };

 // List of alternative codes
 typedef std::deque<InstructionCode> InstructionCodeList;

 bool O1{ true }; // Optimization

 using OP_T = std::vector<uint8_t>;

 InstructionCodeList op_jmp(const std::vector<Token>& sl, std::vector<uint8_t> op_bytes_8, std::vector<uint8_t> op_bytes_32)
 {
  if (sl.size() == 2) { // JMP rel8 / rel32
   const std::string& label{ sl[1].value };
   InstructionCodeList result;
   if (op_bytes_32.size() > 0) {
    op_bytes_32.resize(op_bytes_32.size() + 4, 0x00);
    result.push_back({ op_bytes_32, { {AddressType::Relative32, op_bytes_32.size() - 4, label} } } );
   }
   if (op_bytes_8.size() > 0 && (O1 || op_bytes_32.size() == 0)) {
    op_bytes_8.push_back(0x00);
    result.push_back({ op_bytes_8, { {AddressType::Relative8, op_bytes_8.size() - 1, label} } });
   }
   return result;
  }

  // ... TODO
  throw std::runtime_error("Unknown command: "s + sl[0].value);
 }

 std::unordered_map<std::string, std::function<InstructionCodeList(const std::vector<Token>&)>> ops{

  // Integer Addition
  {"add", [](const std::vector<Token>& sl) -> InstructionCodeList {
   if (sl.size() == 3) {
    if (sl[1].value == "eax") { // ADD EAX, imm32
     return { { std::vector<uint8_t>{ 0x05 } +imm32(sl[2].value), {} } };
    } else if (sl[1].value == "rax") { // ADD RAX, imm32
     return  { { REX("W") + std::vector<uint8_t>{ 0x05 } +imm32(sl[2].value), {} } };
    }
   }

   // ... TODO
   throw std::runtime_error("Unknown command: "s + sl[0].value);
  }},

  // Call Procedure
  {"call",  std::bind(op_jmp, _1, OP_T{}, OP_T{ 0xE8 })},

  // Interrupt
  {"int", [](const std::vector<Token>& sl) -> InstructionCodeList {
   if (sl.size() == 2) {
    if (sl[1].value == "0") { // INT 0
     return { { std::vector<uint8_t>{ 0xCE }} };
    } else if (sl[1].value == "1") { // INT 1
     return { { std::vector<uint8_t>{ 0xF1 }} };
    } else if (sl[1].value == "3") { // INT 3
     return { { std::vector<uint8_t>{ 0xCC }} };
    } else { // INT <...>
     return  { { std::vector<uint8_t>{ 0xCD } +imm8(sl[2].value) } };
    }
   }

   // ... TODO
   throw std::runtime_error("Unknown command: "s + sl[0].value);
  }},

  // Unconditional Jump
  {"jmp", std::bind(op_jmp, _1, OP_T{ 0xEB }, OP_T{ 0xE9 })},

  // Conditional Jumps
  {"ja",     std::bind(op_jmp, _1, OP_T{ 0x77 }, OP_T{ 0x0F, 0x87 })},
  {"jae",    std::bind(op_jmp, _1, OP_T{ 0x73 }, OP_T{ 0x0F, 0x83 })},
  {"jb",     std::bind(op_jmp, _1, OP_T{ 0x72 }, OP_T{ 0x0F, 0x82 })},
  {"jbe",    std::bind(op_jmp, _1, OP_T{ 0x76 }, OP_T{ 0x0F, 0x86 })},
  {"jc",     std::bind(op_jmp, _1, OP_T{ 0x72 }, OP_T{ 0x0F, 0x82 })},
  {"jecxz",  std::bind(op_jmp, _1, OP_T{ 0xE3 }, OP_T{})},
  {"jrcxz",  std::bind(op_jmp, _1, OP_T{ 0xE3 }, OP_T{})},
  {"je",     std::bind(op_jmp, _1, OP_T{ 0x74 }, OP_T{ 0x0F, 0x84 })},
  {"jg",     std::bind(op_jmp, _1, OP_T{ 0x7F }, OP_T{ 0x0F, 0x8F })},
  {"jge",    std::bind(op_jmp, _1, OP_T{ 0x7D }, OP_T{ 0x0F, 0x8D })},
  {"jl",     std::bind(op_jmp, _1, OP_T{ 0x7C }, OP_T{ 0x0F, 0x8C })},
  {"jle",    std::bind(op_jmp, _1, OP_T{ 0x7E }, OP_T{ 0x0F, 0x8E })},
  {"jna",    std::bind(op_jmp, _1, OP_T{ 0x76 }, OP_T{ 0x0F, 0x86 })},
  {"jnae",   std::bind(op_jmp, _1, OP_T{ 0x72 }, OP_T{ 0x0F, 0x82 })},
  {"jnb",    std::bind(op_jmp, _1, OP_T{ 0x73 }, OP_T{ 0x0F, 0x83 })},
  {"jnbe",   std::bind(op_jmp, _1, OP_T{ 0x77 }, OP_T{ 0x0F, 0x87 })},
  {"jnc",    std::bind(op_jmp, _1, OP_T{ 0x73 }, OP_T{ 0x0F, 0x83 })},
  {"jne",    std::bind(op_jmp, _1, OP_T{ 0x75 }, OP_T{ 0x0F, 0x85 })},
  {"jng",    std::bind(op_jmp, _1, OP_T{ 0x7E }, OP_T{ 0x0F, 0x8E })},
  {"jnge",   std::bind(op_jmp, _1, OP_T{ 0x7C }, OP_T{ 0x0F, 0x8C })},
  {"jnl",    std::bind(op_jmp, _1, OP_T{ 0x7D }, OP_T{ 0x0F, 0x8D })},
  {"jnle",   std::bind(op_jmp, _1, OP_T{ 0x7F }, OP_T{ 0x0F, 0x8F })},
  {"jno",    std::bind(op_jmp, _1, OP_T{ 0x71 }, OP_T{ 0x0F, 0x81 })},
  {"jnp",    std::bind(op_jmp, _1, OP_T{ 0x7B }, OP_T{ 0x0F, 0x8B })},
  {"jns",    std::bind(op_jmp, _1, OP_T{ 0x79 }, OP_T{ 0x0F, 0x89 })},
  {"jnz",    std::bind(op_jmp, _1, OP_T{ 0x75 }, OP_T{ 0x0F, 0x85 })},
  {"jo",     std::bind(op_jmp, _1, OP_T{ 0x70 }, OP_T{ 0x0F, 0x80 })},
  {"jp",     std::bind(op_jmp, _1, OP_T{ 0x7A }, OP_T{ 0x0F, 0x8A })},
  {"jpe",    std::bind(op_jmp, _1, OP_T{ 0x7A }, OP_T{ 0x0F, 0x8A })},
  {"jpo",    std::bind(op_jmp, _1, OP_T{ 0x7B }, OP_T{ 0x0F, 0x8B })},
  {"js",     std::bind(op_jmp, _1, OP_T{ 0x78 }, OP_T{ 0x0F, 0x88 })},
  {"jz",     std::bind(op_jmp, _1, OP_T{ 0x74 }, OP_T{ 0x0F, 0x84 })},

  // Memory Move
  { "mov", [](const std::vector<Token>& sl) -> InstructionCodeList {
   if (sl.size() == 3) {
    return { { std::vector<uint8_t>{ 0x88 } + ModRM(sl[2].value, sl[1].value), {} } };  // r/m8, r8: ModRM:r/m (w), ModRM:reg (r)
   }

   // ... TODO
   throw std::runtime_error("Unknown command: "s + sl[0].value);
  }},

  // No Operation
  { "nop", [](const std::vector<Token>& sl) -> InstructionCodeList {
   return {{ std::vector<uint8_t>{ 0x90 }, {}}};
  }},

  // Return from procedure
  { "ret", [](const std::vector<Token>& sl) -> InstructionCodeList {
   return {{ std::vector<uint8_t>{ 0xC3 }, {}}}; // near return; TODO: far return is 0xCB
  }},

  { "xor", [](const std::vector<Token>& sl) -> InstructionCodeList {
   if (sl.size() == 3) {
    return { { std::vector<uint8_t>{ 0x33 } + ModRM(sl[1].value, sl[2].value) } };  // r8, r/m8: ModRM:reg (w), ModRM:r/m (r)
   }

   // ... TODO
   throw std::runtime_error("Unknown command: "s + sl[0].value);
  }},

 };

#if 0
 prefixes{
  "lock", 0xf0,

  // branch hint
  0x2e, "branch not taken"
  0x3e, "branch taken"

  0x66, "operand size override" // switch between 16 and 32 bit operands
  0x67, "address size override" // switch between 16 and 32 bit addresses
 };
 };
#endif

#ifdef ASM_PARSER
 BNF GetBNF() {
  // TODO:
  return {
   { "assembler-unit", {
    {}
   }},
   { "immediate-32", {
    {}
   }},
   { "mnemonic", {
    {}
   }},
   { "register", {
    {}
   }},
   { "register-8", {
    {}
   }},
   { "register-16", {
    {}
   }},
   { "register-32", {
    {}
   }},
   { "register-64", {
    {}
   }},
 
  };
 };
#endif
 
 // Checks a 32 bit relative address if it's valid as 8 bit address
 bool IsSmallAddress(const InstructionCode& insn) {
  if (insn.addresses.size() != 1)
   throw std::runtime_error("Bad number of addresses in insn");

  size_t i{insn.addresses[0].position};

  if (i > insn.machine_code.size() - 3)
   throw std::runtime_error("Bad Address index "s + std::to_string(i) + " in insn with "s + std::to_string(insn.machine_code.size()) + " bytes"s);

  if (std::count(insn.machine_code.begin() + i, insn.machine_code.begin() + i + 3, 0x00) == 3 ||
   std::count(insn.machine_code.begin() + i, insn.machine_code.begin() + i + 3, 0xFF) == 3)
   return true;

  return false;
 }


} // namespace

class Assembler {

 std::unordered_map<std::string, size_t> labels; ///< labels with their positions in instruction list

 /// 1st Level: Instructions
 /// 2nd Level: Alternatives
 /// 3rd Level: Bytes of single instruction
 std::vector<InstructionCodeList> insn_list;

 uint64_t addressFromInstructionIndex(size_t index)
 {
  // TODO: cache this to prevent repetitive summing

  if (index > insn_list.size())
   throw std::runtime_error("Index "s + std::to_string(index) + " out of range ("s + std::to_string(insn_list.size()) + ")"s);

  uint64_t sum{};

  for (size_t i = 0; i < index; i++) {
   if (insn_list[i].size() < 1) {
    throw std::runtime_error("Insufficient alternatives at index "s + std::to_string(i));
   }

   sum += static_cast<uint64_t>(insn_list[i][0].machine_code.size());
  }

  return sum;
 }

 uint64_t addressFromLabel(std::string label)
 {
  auto it{ labels.find(label) };
  if (it == labels.end())
   throw std::runtime_error("Label not found: "s + label);

  return addressFromInstructionIndex(it->second);
 }

 std::unordered_map<AddressType, std::function<void(std::vector<uint8_t>&, const Address&, uint64_t)>> addressInserters{
  {AddressType::Relative8,  [&](std::vector<uint8_t>& machine_code, const Address& target_address, uint64_t insn_address)
   {
    int64_t difference = static_cast<int64_t>(addressFromLabel(target_address.label)) - insn_address;
    if (difference < -128 || difference > 127)
     throw std::runtime_error("Distance too big");

    int8_t diff8 = static_cast<int8_t>(difference);
    uint8_t diff_u8 = *reinterpret_cast<uint8_t*>(&diff8);

    machine_code[target_address.position] = diff_u8;
   }
  },
  {AddressType::Relative16, [&](std::vector<uint8_t>& machine_code, const Address& target_address, uint64_t insn_address) { throw std::runtime_error("Relative16 Address not yet supported."); }},
  {AddressType::Relative32, [&](std::vector<uint8_t>& machine_code, const Address& target_address, uint64_t insn_address)
   {
    int64_t difference = static_cast<int64_t>(addressFromLabel(target_address.label)) - insn_address;
    if (difference < -4294967296 || difference > 4294967295)
     throw std::runtime_error("Distance too big");

    int32_t diff32 = static_cast<int32_t>(difference);
    uint32_t diff_u32 = *reinterpret_cast<uint32_t*>(&diff32);

    machine_code[target_address.position] = diff_u32 & 0xFF; // little endian
    machine_code[target_address.position + 1] = diff_u32 >> 8 & 0xFF;
    machine_code[target_address.position + 2] = diff_u32 >> 16 & 0xFF;
    machine_code[target_address.position + 3] = diff_u32 >> 24 & 0xFF;
   }
  },
  {AddressType::Absolute8,  [&](std::vector<uint8_t>& machine_code, const Address& target_address, uint64_t insn_address) {throw std::runtime_error("Absolute8 Address not yet supported."); }},
  {AddressType::Absolute16, [&](std::vector<uint8_t>& machine_code, const Address& target_address, uint64_t insn_address) {throw std::runtime_error("Absolute16 Address not yet supported."); }},
  {AddressType::Absolute32, [&](std::vector<uint8_t>& machine_code, const Address& target_address, uint64_t insn_address) {throw std::runtime_error("Absolute32 Address not yet supported."); }},
 };

 void produce_machine_code(std::vector<std::vector<Token>>& tl)
 {
  for (const auto& t : tl) {
   // label:
   // label: mnemonic arg1, arg2, arg3
   //        mnemonic arg1, arg2, arg3

   if (t.size() == 2 && t[0].type == "label" && t[1].type == ":") { // label
    if (labels.find(t[0].value) != labels.end())
     throw std::runtime_error("Label already defined: "s + t[0].value);

    labels[t[0].value] = insn_list.size();
   } else if (t.size() >= 1 && t[0].type == "instruction") { // instruction
    std::string instruction{ t[0].value };
    auto it = ops.find(instruction);
    if (it == ops.end())
     throw std::runtime_error("Unknown instruction: "s + instruction);

    InstructionCodeList codes = it->second(t);

    if (codes.size() == 0)
     throw std::runtime_error("No instruction generated");

    insn_list.push_back(codes);

   } else
    throw std::runtime_error("Syntax error"s);
  }
 }

 void insert_addresses()
 {
  for (size_t i = 0; i < insn_list.size(); i++) {
   InstructionCodeList& list{ insn_list[i] };
   if (list.size() == 0)
    throw std::runtime_error("No instruction at index "s + std::to_string(i));

   InstructionCode& code{ list[0] };

   for (const auto& address : code.addresses) {
    addressInserters[address.type](code.machine_code, address, addressFromInstructionIndex(i));
   }
  }
 }

 void optimize()
 {
  // reduce Jump sizes via alternatives if possible
  bool changed{};
  do {
   changed = false;

   for (size_t i = 0; i < insn_list.size(); i++) {
    InstructionCodeList& list{ insn_list[i] }; // Alternatives

    // apply specific heuristics to optimization case
    if (list.size() == 2) {
     if (list[0].addresses.size() == 1 && list[1].addresses.size() == 1) {
      if (list[0].addresses[0].type == AddressType::Relative32 && list[1].addresses[0].type == AddressType::Relative8) {
       if (IsSmallAddress(list[0])) {
        list.pop_front();
        break; // start over from start of program
       }
      }
     }
    }
   }

   if (changed)
    insert_addresses(); // update

  } while (changed);
 }

 std::vector<uint8_t> collect_code()
 {
  std::vector<uint8_t> result;

  // collect generated machine instructions for result
  // Alternatives already resolved, if configured. Consider only 1st entry (no matter if optimized or not).
  for (size_t i = 0; i < insn_list.size(); i++) {
   InstructionCodeList& list{ insn_list[i] };
   if (list.size() == 0)
    throw std::runtime_error("No instruction at index "s + std::to_string(i));

   InstructionCode& code{ list[0] };

   result.insert(result.end(), code.machine_code.begin(), code.machine_code.end());
  }

  return result;
 }

public:
 Assembler() {}

 std::vector<uint8_t> assemble(std::vector<std::vector<Token>> tl)
 {
  labels.clear();
  insn_list.clear();

  produce_machine_code(tl); // 1st pass
  insert_addresses(); // 2nd pass
  if (O1) {
   optimize(); // 3rd pass
  }

  return collect_code(); // 4th pass
 }

}; // class Assembler