//+------------------------------------------------------------------+
//|                                      SmartLotCalculator.mqh       |
//|                     Open-source position sizing library for MQL5  |
//+------------------------------------------------------------------+
#ifndef SMART_LOT_CALCULATOR_MQH
#define SMART_LOT_CALCULATOR_MQH

// Account value used as the basis for percentage risk.
enum ENUM_RISK_BASE
{
   RISK_BASE_BALANCE = 0,
   RISK_BASE_EQUITY = 1,
   RISK_BASE_FREE_MARGIN = 2
};

//+------------------------------------------------------------------+
//| Smart lot calculator                                             |
//+------------------------------------------------------------------+
class CSmartLotCalculator
{
private:

   // Returns the selected account value.
   static double GetRiskBaseValue(const ENUM_RISK_BASE risk_base)
   {
      switch(risk_base)
      {
         case RISK_BASE_BALANCE:
            return AccountInfoDouble(ACCOUNT_BALANCE);

         case RISK_BASE_EQUITY:
            return AccountInfoDouble(ACCOUNT_EQUITY);

         case RISK_BASE_FREE_MARGIN:
            return AccountInfoDouble(ACCOUNT_MARGIN_FREE);
      }

      return 0.0;
   }

   // Determines the number of decimal places required for displaying volume.
   static int GetVolumeDigits(const double volume_step)
   {
      if(volume_step <= 0.0)
         return 2;

      int digits = 0;
      double normalized_step = volume_step;

      while(digits < 8 &&
            MathAbs(normalized_step - MathRound(normalized_step)) > 1e-8)
      {
         normalized_step *= 10.0;
         digits++;
      }

      return digits;
   }

   // Validates basic calculation parameters.
   static bool ValidateParameters(const string symbol,
                                  const ENUM_ORDER_TYPE order_type,
                                  const double entry_price,
                                  const double stop_price,
                                  string &error)
   {
      error = "";

      if(symbol == "")
      {
         error = "The symbol name is empty.";
         return false;
      }

      if(order_type != ORDER_TYPE_BUY &&
         order_type != ORDER_TYPE_SELL)
      {
         error = "Only ORDER_TYPE_BUY and ORDER_TYPE_SELL are supported.";
         return false;
      }

      if(entry_price <= 0.0)
      {
         error = "The entry price must be greater than zero.";
         return false;
      }

      if(stop_price <= 0.0)
      {
         error = "The Stop Loss price must be greater than zero.";
         return false;
      }

      if(entry_price == stop_price)
      {
         error = "The entry price and Stop Loss price cannot be equal.";
         return false;
      }

      if(order_type == ORDER_TYPE_BUY && stop_price >= entry_price)
      {
         error = "For a buy calculation, the Stop Loss must be below the entry price.";
         return false;
      }

      if(order_type == ORDER_TYPE_SELL && stop_price <= entry_price)
      {
         error = "For a sell calculation, the Stop Loss must be above the entry price.";
         return false;
      }

      if(!SymbolSelect(symbol, true))
      {
         error = "The symbol could not be selected in Market Watch.";
         return false;
      }

      return true;
   }

public:

   // Normalizes volume to the broker's allowed volume step.
   // The volume is rounded down so the selected risk is not exceeded.
   static double NormalizeVolume(const string symbol,
                                 const double requested_volume,
                                 string &error)
   {
      error = "";

      if(requested_volume <= 0.0)
      {
         error = "The requested volume must be greater than zero.";
         return 0.0;
      }

      double volume_min  = SymbolInfoDouble(symbol, SYMBOL_VOLUME_MIN);
      double volume_max  = SymbolInfoDouble(symbol, SYMBOL_VOLUME_MAX);
      double volume_step = SymbolInfoDouble(symbol, SYMBOL_VOLUME_STEP);

      if(volume_min <= 0.0 ||
         volume_max <= 0.0 ||
         volume_step <= 0.0)
      {
         error = "Invalid volume specifications received from the broker.";
         return 0.0;
      }

      if(requested_volume < volume_min)
      {
         error = StringFormat(
            "Calculated volume %.8f is below the broker minimum of %.8f lots.",
            requested_volume,
            volume_min
         );

         return 0.0;
      }

      double limited_volume = MathMin(requested_volume, volume_max);

      // Normalize relative to the minimum volume. This also handles cases
      // where the minimum volume and the volume step are different.
      double steps = MathFloor(
         ((limited_volume - volume_min) / volume_step) + 1e-10
      );

      double normalized_volume = volume_min + (steps * volume_step);

      normalized_volume = MathMax(normalized_volume, volume_min);
      normalized_volume = MathMin(normalized_volume, volume_max);

      int volume_digits = GetVolumeDigits(volume_step);

      return NormalizeDouble(normalized_volume, volume_digits);
   }

   // Calculates the potential loss for a given volume.
   static double CalculatePotentialLoss(const string symbol,
                                        const ENUM_ORDER_TYPE order_type,
                                        const double volume,
                                        const double entry_price,
                                        const double stop_price,
                                        string &error)
   {
      error = "";

      if(!ValidateParameters(
         symbol,
         order_type,
         entry_price,
         stop_price,
         error
      ))
      {
         return 0.0;
      }

      if(volume <= 0.0)
      {
         error = "The volume must be greater than zero.";
         return 0.0;
      }

      double calculated_profit = 0.0;

      ResetLastError();

      bool calculation_success = OrderCalcProfit(
         order_type,
         symbol,
         volume,
         entry_price,
         stop_price,
         calculated_profit
      );

      if(!calculation_success)
      {
         error = StringFormat(
            "OrderCalcProfit failed. MetaTrader error code: %d.",
            GetLastError()
         );

         return 0.0;
      }

      double potential_loss = MathAbs(calculated_profit);

      if(potential_loss <= 0.0)
      {
         error = "MetaTrader returned a zero potential loss.";
         return 0.0;
      }

      return potential_loss;
   }

   // Calculates volume from a fixed amount of account currency.
   static double CalculateByMoney(const string symbol,
                                  const ENUM_ORDER_TYPE order_type,
                                  const double entry_price,
                                  const double stop_price,
                                  const double risk_money,
                                  string &error)
   {
      error = "";

      if(risk_money <= 0.0)
      {
         error = "Risk money must be greater than zero.";
         return 0.0;
      }

      if(!ValidateParameters(
         symbol,
         order_type,
         entry_price,
         stop_price,
         error
      ))
      {
         return 0.0;
      }

      // Calculate how much one complete lot would lose at the Stop Loss.
      double loss_for_one_lot = CalculatePotentialLoss(
         symbol,
         order_type,
         1.0,
         entry_price,
         stop_price,
         error
      );

      if(loss_for_one_lot <= 0.0)
         return 0.0;

      double raw_volume = risk_money / loss_for_one_lot;

      return NormalizeVolume(symbol, raw_volume, error);
   }

   // Calculates volume from a percentage of balance, equity or free margin.
   static double CalculateByRiskPercent(const string symbol,
                                        const ENUM_ORDER_TYPE order_type,
                                        const double entry_price,
                                        const double stop_price,
                                        const double risk_percent,
                                        const ENUM_RISK_BASE risk_base,
                                        string &error)
   {
      error = "";

      if(risk_percent <= 0.0)
      {
         error = "Risk percentage must be greater than zero.";
         return 0.0;
      }

      double base_value = GetRiskBaseValue(risk_base);

      if(base_value <= 0.0)
      {
         error = "The selected account risk base is unavailable or zero.";
         return 0.0;
      }

      double risk_money = base_value * risk_percent / 100.0;

      return CalculateByMoney(
         symbol,
         order_type,
         entry_price,
         stop_price,
         risk_money,
         error
      );
   }
};

#endif