//+------------------------------------------------------------------+
//|                                       AlgoGen.KeltnerChannel.mq4 |
//|                                          Copyright 2020, AlgoGen |
//|                                           https://www.algogen.io |
//+------------------------------------------------------------------+
input ENUM_APPLIED_PRICE priceMode = PRICE_TYPICAL; // Price
input ENUM_MA_METHOD movingAverageMode = MODE_EMA; // Moving Average
input int movingAveragePeriod = 21; // Keltner Channel Moving Average Period
input int atrPeriod = 21; // Keltner Channel ATR Period 
input double multiplier = 3.0; // Keltner Channel ATR Multiplier

#property copyright "Copyright 2020, AlgoGen."
#property link      "https://www.algogen.io"
#property version   "1.00"
#property strict

#property indicator_chart_window
#property indicator_buffers 3
#property indicator_plots   3

#property indicator_label1  "UPPER"
#property indicator_type1   DRAW_LINE
#property indicator_color1  clrRed
#property indicator_style1  STYLE_SOLID
#property indicator_width1  1

#property indicator_label2  "MAIN"
#property indicator_type2   DRAW_LINE
#property indicator_color2  clrRed
#property indicator_style2  STYLE_SOLID
#property indicator_width2  1

#property indicator_label3  "LOWER"
#property indicator_type3   DRAW_LINE
#property indicator_color3  clrRed
#property indicator_style3  STYLE_SOLID
#property indicator_width3  1

double UPPERBuffer[];
double MAINBuffer[];
double LOWERBuffer[];

//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int OnInit() {
    SetIndexBuffer(0, UPPERBuffer);
    SetIndexBuffer(1, MAINBuffer);
    SetIndexBuffer(2, LOWERBuffer);

    return (INIT_SUCCEEDED);
}

//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
int OnCalculate(
        const int rates_total,
        const int prev_calculated,
        const datetime &time[],
        const double &open[],
        const double &high[],
        const double &low[],
        const double &close[],
        const long &tick_volume[],
        const long &volume[],
        const int &spread[]
) {
    int limit;
    int countedBars = IndicatorCounted();
    if (countedBars < 0) return (-1);
    if (countedBars > 0) countedBars--;
    limit = Bars - countedBars;

    for (int i = 0; i < limit; i++) {
        double middle = iMA(NULL, 0, movingAveragePeriod, 0, movingAverageMode, priceMode, i);
        double atr = iATR(NULL, 0, atrPeriod, i);
        double upper = middle + multiplier * atr;
        double lower = middle - multiplier * atr;

        UPPERBuffer[i] = upper;
        MAINBuffer[i] = middle;
        LOWERBuffer[i] = lower;
    }

    return 0;
}

iCustom(
    // symbol 
    NULL,
    // timeframe
    0,
    // name 
    "AlgoGen.KeltnerChannel",
    // applied price,
    PRICE_CLOSE,
    // moving average,
    MODE_EMA,
    // moving average period
    21,
    // atr period
    14,
    // atr multiplier
    3,
    // line index
    0,
    // shift
    0
)