#include <TF1.h>
#include <TCanvas.h>
#include <TGraph.h>

std::vector <Double_t> initialParams = {-9.25005e-06, 0.00201326, 5, -0.000335604, 0.00201326, -2.49909e-07, -5.22527e-11, -5.50176e-14};
	
Double_t rangeLow = 0;
Double_t rangeHigh = 3000;
Int_t nPars = 5;
Double_t fitf(Double_t *x, Double_t *par)
{
	Double_t X = x[0];

	Double_t func = par[0]*TMath::Exp(par[1]*X);
	Int_t N = (int) par[2];
	for( int n = 0; n < N; n++ )
	{
		Double_t monomio = par[3+n];
		for( int m = 0; m < n; m++ )
		   monomio *= x[0];	
		func += monomio;
	}

	return func;
}

void BxFit_0()
{
   std::ifstream file("outFinal_Xp.txt");
    if (!file.is_open()) {
        std::cerr << "Error: Unable to open file out.txt" << std::endl;
        return;
    }

    // Variables to store data
    double z, Bx, By, Bz;
    std::vector<double> xData, yData;

    // Read data from the file
    while (file >> z >> Bx >> By >> Bz ) {
        xData.push_back(z);
        yData.push_back(Bx);
    }
    file.close();

    // Create a TGraph object
    TGraph *graph = new TGraph(xData.size(), &xData[0], &yData[0]);

    // Optionally customize the appearance of the graph
    graph->SetLineColor(kBlue);
    graph->SetLineWidth(1);
    graph->SetMarkerStyle(20);
    graph->SetMarkerSize(0.5);

	// Create a canvas to draw the graph
    TCanvas *canvas = new TCanvas("canvas", "Graph from ASCII file", 800, 600);

    // Optionally, add a title and labels
    graph->SetTitle("Graph from ASCII file");
    graph->GetXaxis()->SetTitle("X Axis Title");
    graph->GetYaxis()->SetTitle("Y Axis Title");
	graph->GetXaxis()->SetLimits(rangeLow,rangeHigh);
	graph->GetYaxis()->SetRangeUser(-0.01,0);

    graph->Draw("AP"); // A: Axis, P: Points, L: Lines

    // Update the canvas
    canvas->Update();

   // Creates a Root function based on function fitf above
   TF1 *fn = new TF1("fitf", fitf, rangeLow, rangeHigh, 3+nPars);
   
   for( int n = 0; n < initialParams.size(); n++ )
       fn->SetParameter(n, initialParams[n] );

   /////// Fixing or limiting parameters of exponential //////
   fn->SetParLimits(0,0.8*initialParams[0],1.2*initialParams[0]);
   fn->SetParLimits(1,0.8*initialParams[1],1.2*initialParams[1]);
   //fn->FixParameter(0,initialParams[0]);
   //fn->FixParameter(1,initialParams[1]);

   fn->FixParameter(2,nPars);

   // We do a first fit considering only the ATan function
   graph->Fit("fitf","R", "", rangeLow, rangeHigh);

   fn->SetLineColor(kRed);
   fn->Draw("same");

   canvas->Update();
}