-- More information about this indicator can be found at:
-- http://fxcodebase.com/code/viewtopic.php?f=17&t=60132
-- Id: 11606

--+------------------------------------------------------------------+
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--+------------------------------------------------------------------+
function Init()
    indicator:name("Gopalakrishnan Range Index");
    indicator:description("Gopalakrishnan Range Index");
    indicator:requiredSource(core.Bar);
    indicator:type(core.Oscillator);
    indicator.parameters:addGroup("Calculation");
    indicator.parameters:addInteger("Period", "Period", "Period", 14);
	indicator.parameters:addGroup("Style");
    indicator.parameters:addColor("GAPO_color", "Color of GAPO", "Color of GAPO", core.rgb(255, 0, 0));
	indicator.parameters:addInteger("width", "Line width", "", 1, 1, 5);
    indicator.parameters:addInteger("style", "Line style", "", core.LINE_SOLID);
    indicator.parameters:setFlag("style", core.FLAG_LINE_STYLE);
end

-- Indicator instance initialization routine
-- Processes indicator parameters and creates output streams
-- TODO: Refine the first period calculation for each of the output streams.
-- TODO: Calculate all constants, create instances all subsequent indicators and load all required libraries
-- Parameters block
local Period;

local first;
local source = nil;

-- Streams block
local GAPO = nil;

-- Routine
function Prepare(nameOnly)
    Period = instance.parameters.Period;
    source = instance.source;
    first = source:first()+Period;

    local name = profile:id() .. "(" .. source:name() .. ", " .. tostring(Period) .. ")";
    instance:name(name);

    if (not (nameOnly)) then
        GAPO = instance:addStream("GAPO", core.Line, name, "GAPO", instance.parameters.GAPO_color, first);
    GAPO:setPrecision(math.max(2, instance.source:getPrecision()));
		GAPO:setWidth(instance.parameters.width);
        GAPO:setStyle(instance.parameters.style);
    end
end

-- Indicator calculation routine
-- TODO: Add your code for calculation output values
function Update(period)
    if period < first or not  source:hasData(period) then
	return;
	end
	
	--GAPO(t) = Log( HH(t) – LL(t) ) / Log(n)
	    local min,max= mathex.minmax(source, period-Period+1, period);
        GAPO[period] = math.log(max-min)/math.log(Period);
    
end