//+------------------------------------------------------------------+
//|                                                          RSI.mq5 |
//|                             Copyright 2000-2025, MetaQuotes Ltd. |
//|                                             https://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright   "Copyright 2000-2025, MetaQuotes Ltd."
#property link        "https://www.mql5.com"
#property description "Relative Strength Index"
//--- indicator settings
#property indicator_separate_window
#property indicator_minimum 0
#property indicator_maximum 100
#property indicator_level1 30
#property indicator_level2 70
#property indicator_buffers 3
#property indicator_plots   1
#property indicator_type1   DRAW_LINE
#property indicator_color1  clrDodgerBlue
//--- input parameters
input int InpPeriodRSI=14; // Period
//--- indicator buffers
double    ExtRSIBuffer[];
double    ExtPosBuffer[];
double    ExtNegBuffer[];

int       ExtPeriodRSI;
//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
void OnInit()
  {
//--- check for input
   if(InpPeriodRSI<1)
     {
      ExtPeriodRSI=14;
      PrintFormat("Incorrect value for input variable InpPeriodRSI = %d. Indicator will use value %d for calculations.",
                  InpPeriodRSI,ExtPeriodRSI);
     }
   else
      ExtPeriodRSI=InpPeriodRSI;
//--- indicator buffers mapping
   SetIndexBuffer(0,ExtRSIBuffer,INDICATOR_DATA);
   SetIndexBuffer(1,ExtPosBuffer,INDICATOR_CALCULATIONS);
   SetIndexBuffer(2,ExtNegBuffer,INDICATOR_CALCULATIONS);
//--- set accuracy
   IndicatorSetInteger(INDICATOR_DIGITS,2);
//--- sets first bar from what index will be drawn
   PlotIndexSetInteger(0,PLOT_DRAW_BEGIN,ExtPeriodRSI);
//--- name for DataWindow and indicator subwindow label
   IndicatorSetString(INDICATOR_SHORTNAME,"RSI("+string(ExtPeriodRSI)+")");
  }
//+------------------------------------------------------------------+
//| Relative Strength Index                                          |
//+------------------------------------------------------------------+
int OnCalculate(const int rates_total,
                const int prev_calculated,
                const int begin,
                const double &price[])
  {
   if(rates_total<=ExtPeriodRSI)
      return(0);
//--- preliminary calculations
   int pos=prev_calculated-1;
   if(pos<=ExtPeriodRSI)
     {
      double sum_pos=0.0;
      double sum_neg=0.0;
      //--- first RSIPeriod values of the indicator are not calculated
      ExtRSIBuffer[0]=0.0;
      ExtPosBuffer[0]=0.0;
      ExtNegBuffer[0]=0.0;
      for(int i=1; i<=ExtPeriodRSI; i++)
        {
         ExtRSIBuffer[i]=0.0;
         ExtPosBuffer[i]=0.0;
         ExtNegBuffer[i]=0.0;
         double diff=price[i]-price[i-1];
         sum_pos+=(diff>0?diff:0);
         sum_neg+=(diff<0?-diff:0);
        }
      //--- calculate first visible value
      ExtPosBuffer[ExtPeriodRSI]=sum_pos/ExtPeriodRSI;
      ExtNegBuffer[ExtPeriodRSI]=sum_neg/ExtPeriodRSI;
      if(ExtNegBuffer[ExtPeriodRSI]!=0.0)
         ExtRSIBuffer[ExtPeriodRSI]=100.0-(100.0/(1.0+ExtPosBuffer[ExtPeriodRSI]/ExtNegBuffer[ExtPeriodRSI]));
      else
        {
         if(ExtPosBuffer[ExtPeriodRSI]!=0.0)
            ExtRSIBuffer[ExtPeriodRSI]=100.0;
         else
            ExtRSIBuffer[ExtPeriodRSI]=50.0;
        }
      //--- prepare the position value for main calculation
      pos=ExtPeriodRSI+1;
     }
//--- the main loop of calculations
   for(int i=pos; i<rates_total && !IsStopped(); i++)
     {
      double diff=price[i]-price[i-1];
      ExtPosBuffer[i]=(ExtPosBuffer[i-1]*(ExtPeriodRSI-1)+(diff>0.0?diff:0.0))/ExtPeriodRSI;
      ExtNegBuffer[i]=(ExtNegBuffer[i-1]*(ExtPeriodRSI-1)+(diff<0.0?-diff:0.0))/ExtPeriodRSI;
      if(ExtNegBuffer[i]!=0.0)
         ExtRSIBuffer[i]=100.0-100.0/(1+ExtPosBuffer[i]/ExtNegBuffer[i]);
      else
        {
         if(ExtPosBuffer[i]!=0.0)
            ExtRSIBuffer[i]=100.0;
         else
            ExtRSIBuffer[i]=50.0;
        }
     }
//--- OnCalculate done. Return new prev_calculated.
   return(rates_total);
  }
//+------------------------------------------------------------------+