#pragma once

#include <memory>
#include <stdexcept>
#include <string>
#include <vector>

using namespace std::string_literals;

using code_sequence = std::vector<uint8_t>;

template<typename from_t>
code_sequence to_code_sequence(from_t v);

template<>
code_sequence to_code_sequence<uint16_t>(uint16_t v) {
 return code_sequence{static_cast<uint8_t>(v & 0xFF), static_cast<uint8_t>(v >> 8)};
}

template<>
code_sequence to_code_sequence<uint32_t>(uint32_t v) {
 return code_sequence{static_cast<uint8_t>(v & 0xFF), static_cast<uint8_t>(v >> 8), static_cast<uint8_t>(v >> 16),static_cast<uint8_t>(v >> 24) };
}

uint32_t high_bits(uint8_t number)
{
 return ~((static_cast<uint32_t>(1) << (32 - number)) - 1);
}

// Identify operator with leading bits
class Pattern
{
public:
 Pattern(uint32_t bits, uint32_t mask): _bits{bits}, _mask{mask} {}

 template<typename T>
 T encode()
 {
  return static_cast<T>(_bits);
 }


private:
 uint32_t _bits;
 uint32_t _mask;
};

class Operand
{
protected:
 Operand(uint8_t pos): _pos(pos){}
private:
 uint8_t _pos;
};

class Register: public Operand
{
public:
 Register(uint8_t size, uint8_t pos): Operand{pos} {}
 Register(uint32_t mask): Operand{0} { throw std::runtime_error("Unimplemented"); }
 Register(const std::string& name): Operand{0} { throw std::runtime_error("Unimplemented"); }
};

class SameRegister: public Operand
{
public:
 SameRegister(uint8_t index): Operand{index} {};
};

class Immediate: public Operand
{
public:
 Immediate(uint8_t size, uint8_t pos): Operand{pos}, _bits{size} {}
private:
 uint8_t _bits;
};

using Operands = std::vector<std::shared_ptr<Operand>>;

// Pattern [, Operand, ...]
class Instruction
{
public:
 Instruction(const std::string& mnemonic, uint8_t size, Pattern pattern, Operands operands): _mnemonic(mnemonic), _size(size), _pattern(pattern), _operands(operands) {}
 code_sequence encode(const std::vector<std::string>& arguments)
 {
  if (_size == 2) { // 16 bit thumb insn
   uint16_t result{ _pattern.encode<uint16_t>()};
   return to_code_sequence(result);
  } else if (_size == 4) { // 32 bit thumb insn
   uint32_t result{ _pattern.encode<uint32_t>()};
   return to_code_sequence(result);
  } else {
   throw std::runtime_error("Unsupported instruction size "s + std::to_string(_size));
  }
 }

private:
 std::string _mnemonic;
 uint8_t _size;
 Pattern _pattern;
 Operands _operands;
};

namespace {
 // factory functions
 std::shared_ptr<Operand> imm(uint8_t size, uint8_t pos){ return std::make_shared<Immediate>(size, pos); }
 std::shared_ptr<Operand> reg(uint8_t size, uint8_t pos) { return std::make_shared<Register>(size, pos); }
 std::shared_ptr<Operand> reg(uint32_t mask) { return std::make_shared<Register>(mask); }
 std::shared_ptr<Operand> reg(const std::string& name) { return std::make_shared<Register>(name); }
 std::shared_ptr<Operand> same_reg(uint8_t index) { return std::make_shared<SameRegister>(index); }

 std::shared_ptr<Operand> optional(std::shared_ptr<Operand> op) { return op; }

 // TODO: consistency checks:
 // * all bits defined
 // * unambiguous
 std::vector<Instruction> insns{
  {"adcs", 2, Pattern(0x4140, high_bits(10)), Operands{optional(same_reg(1)), reg(3, 0), reg(3, 3)}}, // T1
  {"adds", 2, Pattern(0x1C00, high_bits(8)), Operands{reg(3, 0), reg(3, 3), imm(3, 6)}}, // T1
  {"adds", 2, Pattern(0x3000, high_bits(5)), Operands{optional(same_reg(1)), reg(3, 8), imm(8, 0)}}, // T2
  {"adds", 2, Pattern(0x1800, high_bits(7)), Operands{reg(3, 0), reg(3, 3), reg(6, 6)}}, // T1
  {"add", 2, Pattern(0x4400, high_bits(8)), Operands{reg(0b10000111), reg(4, 3)}}, // T2
  {"add", 2, Pattern(0xA800, high_bits(5)), Operands{reg(3, 8), imm(8, 0)}}, // T1
  {"add", 2, Pattern(0xB000, high_bits(9)), Operands{optional(reg("sp")), reg("sp"), imm(7, 0)}}, // T2
  {"add", 2, Pattern(0x4468, 0xFF78), Operands{same_reg(2), reg("sp"), reg(0b10000111)}}, // T1
  {"add", 2, Pattern(0x4485, 0xFF87), Operands{reg("sp"), reg(4, 3)}}, // T2

  {"lsls", 2, Pattern(0x0000, high_bits(5)), Operands{reg(3, 0), reg(3, 3), imm(5, 6)}}
 };
};