-- Id: 28
-- Description from the http://www.investopedia.com/articles/trading/03/022603.asp
-- More information about this indicator can be found at:
-- hhttp://fxcodebase.com/code/viewtopic.php?f=17&t=23

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function Init()
    indicator:name("Elder-Ray");
    indicator:description("");
    indicator:requiredSource(core.Bar);
    indicator:type(core.Oscillator);
    indicator.parameters:addGroup("Calculation");	 
    indicator.parameters:addInteger("N", "Number of periods for smoothing", "", 13);
	indicator.parameters:addGroup("Style");
    indicator.parameters:addColor("BullC", "Color of the bull power line", "", core.rgb(255, 0, 0));
	indicator.parameters:addInteger("width1", "Line width", "", 1, 1, 5);
    indicator.parameters:addInteger("style1", "Line style", "", core.LINE_SOLID);
    indicator.parameters:setFlag("style1", core.FLAG_LINE_STYLE);
    indicator.parameters:addColor("BearC", "Color of the bear power line", "", core.rgb(0, 255, 0));
	indicator.parameters:addInteger("width2", "Line width", "", 1, 1, 5);
    indicator.parameters:addInteger("style2", "Line style", "", core.LINE_SOLID);
    indicator.parameters:setFlag("style2", core.FLAG_LINE_STYLE);
end

local source;
local EMA;
local Bull;
local Bear;
local N;
local first;
-- process parameters and prepare for calculations
function Prepare(nameOnly)
    source = instance.source;
	N=instance.parameters.N;
    local name = profile:id() .. "(" .. source:name() .. ", " .. N .. ")";
    instance:name(name);
    if nameOnly then
        return;
    end
    EMA = core.indicators:create("EMA", source.close, N);
	first=EMA.DATA:first();
    Bull = instance:addStream("Bull", core.Line, name .. ".Bull", "Bull", instance.parameters.BullC, first);
    Bull:setPrecision(math.max(2, instance.source:getPrecision()));
	Bull:setWidth(instance.parameters.width1);
    Bull:setStyle(instance.parameters.style1);
    Bear = instance:addStream("Bear", core.Line, name .. ".Bear", "Bear", instance.parameters.BearC, first);
    Bear:setPrecision(math.max(2, instance.source:getPrecision()));
	Bear:setWidth(instance.parameters.width2);
    Bear:setStyle(instance.parameters.style2);
    Bull:addLevel(0);
end

-- Indicator calculation routine
function Update(period, mode)
    EMA:update(mode);

    if  period  < first then
	return;
	end
        Bull[period] = source.high[period] - EMA.DATA[period];
        Bear[period] = source.low[period] - EMA.DATA[period];    
end