package main

import (
	"fmt"
	"time"
)

const (
	width  = 10
	height = 10
)

type Board [][]bool

func NewBoard() Board {
	b := make(Board, height)
	for i := range b {
		b[i] = make([]bool, width)
	}
	return b
}

// sets a cell to alive
func (b Board) SetAlive(x, y int) {
	b[y][x] = true
}

// asks if a cell is alive
func (b Board) IsAlive(x, y int) bool {
	if x < 0 || x >= width || y < 0 || y >= height {
		return false
	}
	return b[y][x]
}

// finds the next state of the board
func (b Board) NextState() Board {
	next := NewBoard()
	for y := 0; y < height; y++ {
		for x := 0; x < width; x++ {
			aliveNeighbors := b.countAliveNeighbors(x, y)
			if b.IsAlive(x, y) {
				next[y][x] = aliveNeighbors == 2 || aliveNeighbors == 3
			} else {
				next[y][x] = aliveNeighbors == 3
			}
		}
	}
	return next
}

// counts the number of alive neighbors for a given cell
func (b Board) countAliveNeighbors(x, y int) int {
	count := 0
	for dy := -1; dy <= 1; dy++ {
		for dx := -1; dx <= 1; dx++ {
			if dx == 0 && dy == 0 {
				continue
			}
			if b.IsAlive(x+dx, y+dy) {
				count++
			}
		}
	}
	return count
}

func (b Board) Print() {
	for y := 0; y < height; y++ {
		for x := 0; x < width; x++ {
			if b.IsAlive(x, y) {
				fmt.Print("O ")
			} else {
				fmt.Print(". ")
			}
		}
		fmt.Println()
	}
	fmt.Println()
}

func main() {
	boards := []Board{
		NewBoard(),
		NewBoard(),
		NewBoard(),
	}

	// glider
	boards[0].SetAlive(1, 0)
	boards[0].SetAlive(2, 1)
	boards[0].SetAlive(0, 2)
	boards[0].SetAlive(1, 2)
	boards[0].SetAlive(2, 2)

	// blinker
	boards[1].SetAlive(1, 0)
	boards[1].SetAlive(1, 1)
	boards[1].SetAlive(1, 2)

	// r-pentomino
	boards[2].SetAlive(3, 3)
	boards[2].SetAlive(4, 3)
	boards[2].SetAlive(2, 4)
	boards[2].SetAlive(3, 4)
	boards[2].SetAlive(3, 5)

	// iterate through each board
	for _, board := range boards {
		for i := 0; i < 10; i++ {
			board.Print()
			board = board.NextState()
			time.Sleep(time.Second / 2)
		}
		fmt.Println("---------------")
	}
}