package q02

import (
	_ "embed"
	"math"
	"math/big"
	"strconv"
	"strings"
	"text/template"

	"github.com/hhhapz/codequest/models"
	"github.com/hhhapz/codequest/question"
)

func init() {
	t := template.New("saturnalia")
	var err error
	t, err = t.Parse(q02Text)
	if err != nil {
		panic(err)
	}
	question.Register(
		&question.Question{
			ID:    "saturnalia",
			Name:  "Saturnalia's Problem",
			Text:  t,
			Level: question.Level1,
			Generate: func(u *models.User) string {
				inp := generate(u)
				var res []string

				for _, n := range inp {
					res = append(res, strconv.Itoa(n))
				}
				return strings.Join(res, "\n")
			},
			Validate: func(u *models.User, part question.Part, solution string) bool {
				return Validate(u, part, solution)
			},
		})
}

func bigLCM(a, b *big.Int) *big.Int {
	return big.NewInt(0).Div(big.NewInt(0).Mul(a, b), big.NewInt(0).GCD(nil, nil, a, b))
}

const (
	ships = 25

	minNum = 3
	maxNum = 100
)

var maxLCM = big.NewInt(math.MaxInt64 / 100)

func generate(u *models.User) []int {
	res := make([]int, 0, ships)

	r := question.UserRandom(u)

	lcm := big.NewInt(1)
	for len(res) != cap(res) {
		n := r.Intn(maxNum-minNum) + minNum

		nLcm := bigLCM(lcm, big.NewInt(int64(n)))
		if nLcm.Cmp(maxLCM) > 0 {
			continue
		}
		lcm = nLcm

		res = append(res, n)
	}
	return res
}

func Validate(u *models.User, p question.Part, sol string) bool {
	inp := generate(u)

	var t int64
	switch p {
	case question.Part1:
		t = solveP1(inp)
	case question.Part2:
		t = solveP2(inp)

	default:
		return false
	}

	return strconv.FormatInt(t, 10) == sol
}

//go:embed q02.md
var q02Text string