//+------------------------------------------------------------------+
//|                                             DonchainChannels.mq4 |
//|                                          Copyright 2023, 100w123 |
//|                                              https://100w123.com |
//+------------------------------------------------------------------+
#property copyright "Copyright 2023, 100w123"
#property link      "https://100w123.com"
#property version   "1.00"
#property strict
#property indicator_chart_window

#property indicator_buffers 3
#property indicator_color1 Red
#property indicator_color2 Blue
#property indicator_color3 Green
#property indicator_width1 1
#property indicator_width2 1
#property indicator_width3 1

double     upper[];
double     middle[];
double     lower[];

input int tch_peroid = 20;
//+------------------------------------------------------------------+
//|                                                                  |
//+------------------------------------------------------------------+
int OnInit() {

    IndicatorShortName("DCH(" + IntegerToString(tch_peroid) + ")");
    //---
    SetIndexBuffer(0, upper);
    SetIndexBuffer(1, middle);
    SetIndexBuffer(2, lower);
    //---
    SetIndexStyle(0, DRAW_LINE);
    SetIndexStyle(1, DRAW_LINE);
    SetIndexStyle(2, DRAW_LINE);
    //---
    SetIndexLabel(0, "Upper");
    SetIndexLabel(1, "Middle");
    SetIndexLabel(2, "Lower");

    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;

    // 第一次回调计算所有 K 线
    if (prev_calculated == 0)
        limit = rates_total - 1;
    else
        limit = rates_total - prev_calculated;      // 后续回调，limit = 0 计算最后一根不断更新的 K 线，当新 K 线形成时, limit = 1，需要计算上一根的最终收盘后的价格和最新形成的一根

    // 最后最新一根索引是 0，从前往后算
    for (int i = limit; i >= 0; i--) {
        upper[i] = iHigh(Symbol(), Period(), iHighest(Symbol(), Period(), MODE_HIGH, tch_peroid, i));
        lower[i] = iLow(Symbol(), Period(), iLowest(Symbol(), Period(), MODE_LOW, tch_peroid, i));
        middle[i] = (upper[i] + lower[i]) / 2;
    }

    return(rates_total);
}
//+------------------------------------------------------------------+