package main

import "fmt"

type game struct {
	turn, lastNumber int
	history          map[int]int
}

func newGame(startingNumbers []int) *game {
	g := game{0, 0, map[int]int{}}
	for _, n := range startingNumbers {
		g.history[g.lastNumber] = g.turn
		g.turn++
		g.lastNumber = n
	}

	return &g
}

func (g *game) takeTurn() (int, int) {
	// fmt.Printf("> Starting turn %d. last: %d\n", g.turn+1, g.lastNumber)
	// fmt.Printf(">> state %+v\n", g)

	var number int

	// Get the new number
	if t, ok := g.history[g.lastNumber]; ok {
		// fmt.Printf(">> We've seen %d before!\n", g.lastNumber)
		// Last number was seen
		number = g.turn - t
	} else {
		// Otherwise the number is zero
		number = 0
	}

	// Store the last turn in history
	g.history[g.lastNumber] = g.turn

	// Go to the next turn
	g.turn++
	g.lastNumber = number

	// fmt.Printf(">> Incrementing turn and updating state %+v\n", g)
	// fmt.Printf("Turn %d spoke \"%d\"\n", g.turn, g.lastNumber)

	return g.turn, g.lastNumber
}

func (g *game) turnTo(targetTurn int) int {
	var n int

	for g.turn < targetTurn {
		_, n = g.takeTurn()
	}

	return n
}

func part1() {
	numbers := []int{16, 12, 1, 0, 15, 7, 11}
	// numbers := []int{0, 3, 6}
	g := newGame(numbers)
	fmt.Println(g)

	t, n := g.takeTurn()
	for t < 2020 {
		t, n = g.takeTurn()
	}

	fmt.Printf("Part 1: Number on turn %d is %d\n", t, n)
}

func part2() {
	numbers := []int{16, 12, 1, 0, 15, 7, 11}
	// numbers := []int{0, 3, 6}
	g := newGame(numbers)
	fmt.Println(g)

	t, n := g.takeTurn()
	for t < 30000000 {
		t, n = g.takeTurn()
	}

	fmt.Printf("Part 2: Number on turn %d is %d\n", t, n)
}

func main() {
	fmt.Println(newGame([]int{16, 12, 1, 0, 15, 7, 11}).turnTo(2020))
	fmt.Println(newGame([]int{16, 12, 1, 0, 15, 7, 11}).turnTo(30000000))
	part1()
	part2()

}