gocollatz/collatz/calculator.go

package collatz

import (
	"collatz/parsing"
	"fmt"
	"math/big"
)

type Calculator struct {
	parser     parsing.Parser
	three      *big.Int
	two        *big.Int
	one        *big.Int
	iterations int
}

func NewCalculator(parser parsing.Parser) *Calculator {
	r := &Calculator{
		parser:     parser,
		three:      big.NewInt(3),
		two:        big.NewInt(2),
		one:        big.NewInt(1),
		iterations: 0,
	}
	return r
}

func (o *Calculator) CalculateCollatz() error {
	number, err := o.parser.Parse()
	if err != nil {
		return fmt.Errorf("couldn't parse input: %w", err)
	}
	fmt.Print(number.Text(10))
	err = o.nextNumber(*number)
	if err != nil {
		return err
	}
	fmt.Println()
	fmt.Println("Iterations:", o.iterations)
	return nil
}

func (o *Calculator) nextNumber(in big.Int) error {
	if in.Cmp(o.one) < 0 {
		return fmt.Errorf("must be greater than 0")
	}
	if in.Cmp(o.one) == 0 {
		return nil
	}
	var newNumber *big.Int
	if new(big.Int).And(&in, o.one).Cmp(o.one) == 0 {
		newNumber = new(big.Int).Add(new(big.Int).Mul(&in, o.three), o.one)
	} else {
		newNumber = new(big.Int).Div(&in, o.two)
	}
	o.iterations++
	fmt.Printf(" -> %s", newNumber.Text(10))
	return o.nextNumber(*newNumber)
}