#include <fstream>
#include <iostream>
#include <cstdlib>
#include <vector>
#include <string>
using namespace std;

void readData(const string &, vector<double> &, vector<double> &);
double interpolation(double, const vector<double> &, const vector<double> &);
bool isOrdered(const vector<double> &);
void reorder(vector<double> &, vector<double> &);

int main(){
    vector<double> a, b;
    double x = -1;
    string filename = "tunnel.dat";
    readData(filename,a,b);
    reorder(a,b);
    x = interpolation(-3.0,a,b);
    cout << endl<< x << endl;
    return 0;
}

void readData(const string &filename, vector<double>& a, vector<double>& b){
    ifstream file;
    double temp;
    file.open(filename);
    if(!file.is_open()){
        cout << "Error opening " << filename << endl;
        exit(1);

    }
    while(file >> temp){
        a.push_back(temp);
        file >> temp;
        b.push_back(temp);
    }
    cout << "readData success" << endl;
}
void reorder(vector<double>& a, vector<double>& b){
    double temp;
    for(unsigned i = 1; i < a.size(); i++){
        for(unsigned j = 0; j < (a.size() - i); j++){
            if(a.at(j) > a.at(j+1)){
                temp = a.at(j);
                a.at(j) = a.at(j+1);
                a.at(j+1) = temp;
                temp = b.at(j);
                b.at(j) = b.at(j+1);
                b.at(j+1) = temp;
            }
        }
    }
    cout << "reorder success" << endl;
}
bool isOrdered(const vector<double>& a){
    for(unsigned i = 0; i+1 < a.size(); i++){
        if(a.at(i) > a.at(i+1)){
            return false;
        }
    }
    return true;
}
double interpolation(double c, const vector<double> &a, const vector<double> &b){

    unsigned index = 1;

    while(a.at(index) < c){
        if(index >= a.size()-1){
        cout << "out of bound";
        exit(1);
        }
        if(a.at(index)==c){
            return b.at(index);
        }
        index++;



    }

    return b.at(index - 1) + ((c - a.at(index - 1))/(a.at(index) - a.at(index - 1))) * (b.at(index) - b.at(index - 1));
}