/*
Copyright © 2025 filifa

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package cmd

import (
	"errors"
	"fmt"
	"log"
	"math/big"

	"github.com/spf13/cobra"
)

func computeSqrtRepetend(x *big.Int) ([]*big.Int, error) {
	m := big.NewInt(0)
	d := big.NewInt(1)
	a0 := new(big.Int).Sqrt(x)

	s := new(big.Int).Exp(a0, big.NewInt(2), nil)
	if x.Cmp(s) == 0 {
		return nil, errors.New("input is a perfect square")
	}

	repetend := make([]*big.Int, 0)

	a := new(big.Int).Set(a0)
	twoa0 := new(big.Int).Mul(big.NewInt(2), a0)
	for a.Cmp(twoa0) != 0 {
		// m = d * a - m
		tmp := new(big.Int)
		m.Sub(tmp.Mul(d, a), m)

		// d = (x - m^2) // d
		tmp.Exp(m, big.NewInt(2), nil)
		d.Div(tmp.Sub(x, tmp), d)

		// a = (a0 + m) // d
		a.Div(tmp.Add(a0, m), d)

		repetend = append(repetend, new(big.Int).Set(a))
	}

	return repetend, nil
}

func sqrtRepetend(cmd *cobra.Command, args []string) {
	x := new(big.Int)

	for _, s := range args {
		_, ok := x.SetString(s, 10)
		if !ok {
			log.Print("invalid input " + s)
			continue
		}

		repetend, err := computeSqrtRepetend(x)
		if err != nil {
			log.Print(s + " is a perfect square")
			continue
		}

		fmt.Print(repetend[0])
		for _, r := range repetend[1:] {
			fmt.Printf(" %s", r)
		}
		fmt.Println()
	}
}

// sqrtRepetendCmd represents the sqrtRepetend command
var sqrtRepetendCmd = &cobra.Command{
	Use:   "sqrt-repetend N [N ...]",
	Short: "Compute the repetend of the square root of the input",
	Long:  `Compute the repetend of the square root of the input.`,
	Args:  cobra.MinimumNArgs(1),
	Run:   sqrtRepetend,
}

func init() {
	rootCmd.AddCommand(sqrtRepetendCmd)

	// Here you will define your flags and configuration settings.

	// Cobra supports Persistent Flags which will work for this command
	// and all subcommands, e.g.:
	// sqrtRepetendCmd.PersistentFlags().String("foo", "", "A help for foo")

	// Cobra supports local flags which will only run when this command
	// is called directly, e.g.:
	// sqrtRepetendCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
}