/*

FakePhysicist.com
admin@fakephysicist.com
13 April 2017

compile with:
g++ v-i_basic.cpp -o v-i_basic `root-config --cflags --libs`

*/

#include <iostream>
#include <iomanip>
#include <cmath>
#include <fstream>
#include <vector>
#include <cstring>

/****** Include the required ROOT Classes *****/
#include "TF1.h"
#include "TStyle.h"
#include "TPad.h"
#include "TCanvas.h"
#include "TGraph.h"
#include "TPostScript.h"
#include "TLatex.h"
#include "TGaxis.h"
#include "TAxis.h"

using namespace std;

int main() {

  ifstream infile("/media/surya/Surya_1/Online/FakePhysicist/1.v-i_basic/vidata_basic.txt"); // Input file name

  vector<double> v_voltage, v_current; // Vector array to store data
  v_voltage.clear();v_current.clear();

  while(!infile.eof()) {
    double voltage, current;
    infile >> voltage >> current;
    cout << " " << voltage
	 << " " << current
	 << endl;
    if(infile.eof()) {break;}	// this one is for extra security. If the last line is not reading then add a extra empty line to the data file.
    v_voltage.push_back(voltage); 
    v_current.push_back(current);
  }

  /************** Now starts the ROOT part ************/

  /*
  Note. Distance units within the canvas are in % of the plots size. Any point on the canvas can be defined by a (x,y) where (0,0) is at the bottom left corner. And the value of x & y varies from 0. to 1. or the fraction of the plot dimension.
  */

  // Setting the Pad/Plot Margins
  gStyle->SetPadBottomMargin(0.14);
  gStyle->SetPadTopMargin(0.09);
  gStyle->SetPadLeftMargin(0.14);
  gStyle->SetPadRightMargin(0.10);

  gStyle->SetOptFit(0);
  // Use 1111 in place of 0 to print statiscis box on the plot
  TGaxis::SetMaxDigits(3);

  // Create pointer of a scatter plot, named as TGraph in ROOT
  // using the above vector array
  TGraph *viplot = new TGraph(v_voltage.size(),&v_current[0],&v_voltage[0]);
  // Here, arguments are number of points, x data, y data
  
  // Now, we need to create a empty Canvas on which
  // the plots will be drawn
  TCanvas *can1 = new TCanvas("V-I Plot","viplot",1200,900);
  // Arguments: name, title, width and height of canvas
  // No space for title

  // Now create a ps file where the plots will be saved
  TPostScript *pss = new TPostScript("viplot.ps",111);
  
  // Now create a new page in that ps file
  pss->NewPage();

  // Select the canvas on which you want to draw
  can1->cd();

  // Then draw the graph
  viplot->Draw("AP*");
  // AP* means it will print all the points as *

  // Now some cosmetic decoration
  viplot->SetTitle("Voltage VS Current Plot");
  viplot->GetXaxis()->SetTitle("Current in A");
  viplot->GetXaxis()->SetTitleSize(0.06);
  viplot->GetXaxis()->SetTitleOffset(1.0);
  viplot->GetXaxis()->CenterTitle();
  viplot->GetXaxis()->SetLabelSize(0.06);
  viplot->GetXaxis()->SetLabelOffset(0.001);
  viplot->GetYaxis()->SetTitle("Voltage in V");
  viplot->GetYaxis()->SetTitleSize(0.06);
  viplot->GetYaxis()->SetTitleOffset(0.9);
  viplot->GetYaxis()->CenterTitle();
  viplot->GetYaxis()->SetLabelSize(0.06);
  viplot->GetYaxis()->SetLabelOffset(0.001);
  
  // Then fit the plot using straight line
  viplot->Fit("pol1");
  // polN is a root defined N order polinomial function

  // Retreive the resistance value which is the slope
  // First, get the fit function from the fitted plot
  TF1 *fitfn1 = (TF1*)viplot->GetFunction("pol1");

  // Then get the slope value and error value which is the
  // second constant/parameter
  double resistance = fitfn1->GetParameter(1);
  double reserror = fitfn1->GetParError(1);

  // Print the resistance value on the plot
  char tempchar[100];
  sprintf(tempchar,"R = (%.0f #pm %.1f) #Omega",resistance,reserror);
  TLatex *Tl = new TLatex(0.4,0.25,tempchar);
  // Bottom left corner position
  Tl->SetNDC(kTRUE);
  Tl->Draw();

  // Update the canvas, otherwise plot will not be written in ps
  can1->Update();

  // Do not forget to close the ps file
  pss->Close();

  return 0;

  // Now compile the code with the command mentioned above
}