#pragma once

#include "./numerics/min.h"
#include "./numerics/max.h"
#include "./numerics/abs.h"

#include "./utils/vector.h"


namespace numerics{
	
	template <typename T>
	struct Base_interp{

		int64_t n, mm;
		int64_t jsav, dj;
		bool cor;
		const T *xx, *yy;


		Base_interp(const utils::Vector<T>& x, const T *y, uint64_t m)
			:n(x.size()), mm(m), jsav(0), cor(false), xx(&x[0]), yy(y){
			//dj = numerics::min(static_cast<int64_t>(1), static_cast<int64_t>(std::pow(static_cast<T>(n), 0.25))); // from NR
			dj = numerics::max(static_cast<int64_t>(1), static_cast<int64_t>(std::pow(static_cast<T>(n), 0.25))); // from chatbot

			if (mm < 2 || n < mm) throw std::invalid_argument("Base_interp: invalid mm or n");
		  	if (!xx || !yy)       throw std::invalid_argument("Base_interp: null data pointers");
		  	if (n < 2)            throw std::invalid_argument("Base_interp: need at least 2 points");

			bool asc = false;
			if (xx[0] < xx[1]){
				asc = true;
			}
			for (int64_t i = 1; i < n; ++i){
				if (!(xx[i] > xx[i-1]) && asc) {
					throw std::invalid_argument("x must be strictly increasing");
				} else if (!(xx[i] < xx[i-1]) && !asc){
        			throw std::invalid_argument("x must be strictly decreasing");
				}
			}
		}

		T interp(T x){
			int64_t jlo;
			if (cor){
				jlo = hunt(x);
			}
			else{
				jlo = locate(x);
			}
			return rawinterp(jlo,x);
		}

		// Derived classes provide this as the actual interpolation method.
		T virtual rawinterp(int64_t jlo, T x) = 0;


		int64_t locate(const T x){
			int64_t ju, jl;
			int64_t jm;

			if (n < 2 || mm < 2 || mm > n){
				throw std::runtime_error("Interpolate: locate size error");	
			}

			bool ascnd = (xx[n-1] >= xx[0]);			// True if ascending order of table, false otherwise.
			jl = 0;										// Initialize lower
			ju = n-1;									// and upper limits.
			while (ju - jl > 1) {						// If we are not yet done,
				jm = (ju+jl) >> 1;						// compute a midpoint,
				if ((x >= xx[jm]) == ascnd){
					jl=jm;								// and replace either the lower limit
				}else{
					ju=jm;								// or the upper limit, as appropriate.
				}
			}											// Repeat until the test condition is satisfied.

			if (std::abs(jl - jsav) > dj){				// Decide whether to use hunt or locate next time.
				cor = false;
			}else{
				cor = true;
			}
			jsav = jl;
			return numerics::max(static_cast<int64_t>(0), numerics::min(n-mm, jl-((mm-2)>>1)));
		}

		int64_t hunt(const T x){
			int64_t jl=jsav, jm, ju, inc=1;

			if (n < 2 || mm < 2 || mm > n){
				throw std::runtime_error("Interpolate: hunt size error");	
			}
			bool ascnd=(xx[n-1] >= xx[0]);				// True if ascending order of table, false otherwise.
			if (jl < 0 || jl > n-1) {					// Input guess not useful. Go immediately to bisection.
				jl=0;
				ju=n-1;
			}else{
				if ((x >= xx[jl]) == ascnd){			// Hunt up:
					for (;;){
						ju = jl + inc;
						if (ju >= n-1){
							ju = n-1;
							break;						// Off end of table.
						}else if((x < xx[ju]) == ascnd){
							break;						// Found bracket.
						}else{							// Not done, so double the increment and try again.
							jl = ju;
							inc += inc;
						}
					}	
				}else{									// Hunt down:
					ju = jl;
					for (;;){
						jl = jl - inc;
						if (jl <= 0){					//Off end of table.
							jl = 0;	
							break;
						}else if((x >= xx[jl]) == ascnd){
							break;						// Found bracket.
						}
						else{							// Not done, so double the increment and try again.
							ju = jl;
							inc += inc;
						}
					}
				}
			}


			while(ju-jl > 1){							// Hunt is done, so begin the final bisection phase:
				jm = (ju+jl) >> 1;
				if ((x >= xx[jm]) == ascnd){
					jl =jm;
				}else{
					ju=jm;
				}
			}
			if (numerics::abs(jl-jsav) > dj){
				cor = false;
			}else{
				cor = true;
			}
			jsav = jl;
			return numerics::max(static_cast<int64_t>(0), numerics::min(n-mm, jl-((mm-2)>>1)));

		}

	};

} // namespace numerics