// A capset is a collection of cards that contains no sets.
// The supposed maximal cardinality of a capset in Set is 20.
// I wish to find such a collection with this program.

package main

import "log"
import "os"
import "fmt"

func is_set(cards []string) bool {
	if len(cards) != 3 {
		log.Fatal("Not the right number of cards.")
	}
	for i := 0; i < 4; i++ {
		if cards[0][i] == cards[1][i] && cards[0][i] == cards[2][i] {
			continue
		}
		if cards[0][i] != cards[1][i] &&
			cards[0][i] != cards[2][i] &&
			cards[1][i] != cards[2][i] {
			continue
		}
		return false
	}
	return true
}

func int2card(num int) string {
	if num < 0 {
		log.Fatal("Number must be nonnegative.")
	}
	if num > 81 {
		log.Fatal("Number must be less than 81.")
	}
	var strlist [4]byte
	for i := 0; i < 4; i++ {
		strlist[3-i] = '0' + byte(num%3)
		num /= 3
	}
	return string(strlist[:])
}

func find_index(deck []string, item string) int {
	for i, v := range deck {
		if v == item {
			return i
		}
	}
	panic("Somehow couldn't find index")
}

func list_pop(arr *[]string) string {
	v := (*arr)[len(*arr)-1]
	*arr = (*arr)[:len(*arr)-1]
	return v
}

func increment_tableau(tableau []string, deck []string, pop bool) []string {
	index := find_index(deck, tableau[len(tableau)-1]) + 1
	if index != len(deck) {
		if pop {
			list_pop(&tableau)
		}
		tableau = append(tableau, deck[index])
		return tableau
	}
	list_pop(&tableau)
	index = find_index(deck, list_pop(&tableau)) + 1
	if len(tableau) == 1 {
		fmt.Println("incrementing second card to index", index)
		if index+18 > len(deck) {
			os.Exit(0)
		}
	}
	tableau = append(tableau, deck[index])
	return tableau
}

func check_tableau(tableau []string) bool {
	if len(tableau) == 2 {
		return true
	}
	var comb [3]string
	for i := 0; i < len(tableau); i++ {
		comb[0] = tableau[i]
		for j := i + 1; j < len(tableau); j++ {
			comb[1] = tableau[j]
			for k := j + 1; k < len(tableau); k++ {
				comb[2] = tableau[k]
				if is_set(comb[:]) {
					return false
				}
			}
		}
	}
	return true
}

func main() {
	outfile, err := os.OpenFile("./capset.out", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
	if err != nil {
		log.Fatal(err)
	}
	defer outfile.Close()
	deck := [81]string{}
	for i := range deck {
		deck[i] = int2card(80-i)
	}
	tableau := []string{deck[0], deck[1]}
	maxim := 20
	for {
		if check_tableau(tableau) {
			if len(tableau) >= maxim {
				fmt.Println(tableau)
				_, err = fmt.Fprintln(outfile, tableau)
				if err != nil {
					log.Println(err)
				}
				err = outfile.Sync()
				if err != nil {
					log.Println(err)
				}
				maxim = len(tableau)
			}
			tableau = increment_tableau(tableau, deck[:], false)
		} else {
			tableau = increment_tableau(tableau, deck[:], true)
		}
	}
}