//+------------------------------------------------------------------+
//|                                                    LotByRisk.mq5 |
//|                                       Copyright 2026, bandersoft |
//|                               https://www.mql5.com/en/users/fats |
//+------------------------------------------------------------------+
//|                                                                  |
//|  Position sizing from a risk percentage - the thing the library  |
//|  is most often wanted for.                                       |
//|                                                                  |
//|  Run it on any chart. It places no orders.                       |
//|                                                                  |
//+------------------------------------------------------------------+
#property copyright "Copyright 2026, bandersoft"
#property link      "https://www.mql5.com/en/users/fats"
#property version   "1.00"
#property script_show_inputs
#property description "Calculates lot size for a given risk percentage and stop distance."

#include <StopFirst\StopFirst.mqh>

input double RiskPercent  = 1.0;    // Risk per trade, % of balance
input double StopLossPips = 30.0;   // Stop distance in pips

//+------------------------------------------------------------------+
//| Script program start function                                    |
//+------------------------------------------------------------------+
void OnStart()
{
   //--- The pip rule is the forex convention. Instruments where a pip
   //--- means something else need telling, or every number below is
   //--- wrong by the same factor:
   //---   SetPipSize("XAUUSD", 0.1);
   double pip = GetPipSize();

   double lots = CalcLotSizeByRisk(RiskPercent, StopLossPips);

   if(lots <= 0)
   {
      //--- 0 is deliberate, not a glitch: the risk budget does not
      //--- cover one minimum lot. Rounding up would risk more than
      //--- was asked for, so the library refuses instead.
      PrintFormat("Cannot size a trade risking %.2f%% over %.1f pips on %s.",
                  RiskPercent, StopLossPips, _Symbol);
      PrintFormat("Minimum lot is %.2f, which needs a wider stop or a larger balance.",
                  SymbolInfoDouble(_Symbol, SYMBOL_VOLUME_MIN));
      return;
   }

   double risked = CalcValueAtRisk(lots, StopLossPips);
   double stopDistance = PipsToPrice(StopLossPips);
   double entry = SymbolInfoDouble(_Symbol, SYMBOL_ASK);

   PrintFormat("%s   1 pip = %s   balance %.2f %s",
               _Symbol, DoubleToString(pip, _Digits),
               AccountInfoDouble(ACCOUNT_BALANCE),
               AccountInfoString(ACCOUNT_CURRENCY));
   PrintFormat("Risking %.2f%% over a %.1f pip stop:", RiskPercent, StopLossPips);
   PrintFormat("   lot size      %.2f", lots);
   PrintFormat("   money at risk %.2f %s", risked, AccountInfoString(ACCOUNT_CURRENCY));
   PrintFormat("   buy at        %s", FormatPrice(entry));
   PrintFormat("   stop at       %s", FormatPrice(entry - stopDistance));
   PrintFormat("   reward:risk   1:%.2f at a %.1f pip target",
               CalcRiskRewardRatio(entry, entry - stopDistance,
                                   entry + stopDistance * 2),
               StopLossPips * 2);
}
//+------------------------------------------------------------------+