package main

import (
	"fmt"
	"math/big"
	"net/http"
	"strconv"
	"time"
)

func calculatePi(n int) *big.Float {
	precision := uint(n * 14)
	pi := new(big.Float).SetPrec(precision)
	pi.SetInt64(0)

	one := new(big.Float).SetInt64(1)
	two := new(big.Float).SetInt64(2)
	four := new(big.Float).SetInt64(4)
	five := new(big.Float).SetInt64(5)
	six := new(big.Float).SetInt64(6)
	eight := new(big.Float).SetInt64(8)
	sixteen := new(big.Float).SetInt64(16)

	for i := 0; i < n; i++ {
		k := new(big.Float).SetInt64(int64(i))

		// Obliczanie 16^i
		powSixteen := new(big.Float).SetInt64(1)
		for j := 0; j < i; j++ {
			powSixteen.Mul(powSixteen, sixteen)
		}

		// Obliczanie 1/16^i
		denominator := new(big.Float).SetPrec(precision)
		if powSixteen.Sign() != 0 {
			denominator.Quo(one, powSixteen)
		} else {
			continue
		}

		// Obliczanie poszczególnych składników
		term1 := new(big.Float).SetPrec(precision)
		term1.Mul(eight, k)
		term1.Add(term1, one)
		term1.Quo(four, term1)

		term2 := new(big.Float).SetPrec(precision)
		term2.Mul(eight, k)
		term2.Add(term2, four)
		term2.Quo(two, term2)

		term3 := new(big.Float).SetPrec(precision)
		term3.Mul(eight, k)
		term3.Add(term3, five)
		term3.Quo(one, term3)

		term4 := new(big.Float).SetPrec(precision)
		term4.Mul(eight, k)
		term4.Add(term4, six)
		term4.Quo(one, term4)

		// Łączenie składników
		sum := new(big.Float).SetPrec(precision)
		sum.Sub(term1, term2)
		sum.Sub(sum, term3)
		sum.Sub(sum, term4)

		// Mnożenie przez 1/16^i i dodawanie do wyniku
		sum.Mul(sum, denominator)
		pi.Add(pi, sum)
	}

	return pi
}

func main() {
	http.HandleFunc("/pi", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Access-Control-Allow-Origin", "*")

		precisionStr := r.URL.Query().Get("precision")
		precision, err := strconv.Atoi(precisionStr)
		if err != nil {
			http.Error(w, "Invalid precision parameter", http.StatusBadRequest)
			return
		}

		start := time.Now()
		pi := calculatePi(precision)
		duration := time.Since(start)

		// Format PI to specified precision
		piFormatted := fmt.Sprintf("%.*f", precision, pi)

		response := fmt.Sprintf(`{"pi": "%s", "time": "%v", "language": "Go"}`, piFormatted, duration)
		w.Header().Set("Content-Type", "application/json")
		fmt.Fprint(w, response)
	})

	fmt.Println("Go server starting on port 8081...")
	http.ListenAndServe(":8081", nil)
}