package main

import (
	"bufio"
	"fmt"
	"os"
	"strings"
)

func main() {
	fmt.Println(part1(readData("example.txt")))
	fmt.Println(part1(readData("data.txt")))
	fmt.Println(part2(readData("example2.txt")))
	fmt.Println(part2(readData("data.txt")))
}

func readData(fileName string) (output []string) {
	fp, err := os.Open(fileName)
	if err != nil {
		panic(err)
	}

	scanner := bufio.NewScanner(fp)
	output = make([]string, 0)

	for scanner.Scan() {
		output = append(output, strings.TrimSpace(scanner.Text()))
	}

	return
}

func part1(s []string) (count int) {
	width := len(s[0])
	height := len(s)

	for y := 0; y < height; y++ {
		for x := 0; x < width; x++ {
			if s[y][x] == 'X' {
				count += checkXmas0(s, x, y)
			}
		}
	}
	return
}

func checkXmas0(s []string, x, y int) (count int) {
	count += checkXmas1(s, x, y, 0)
	if x >= 3 {
		count += checkXmas1(s, x, y, -1)
	}
	if x < len(s[0])-3 {
		count += checkXmas1(s, x, y, 1)
	}
	return
}

func checkXmas1(s []string, x, y, dx int) (count int) {
	count += checkXmas2(s, x, y, dx, 0)
	if y >= 3 {
		count += checkXmas2(s, x, y, dx, -1)
	}
	if y < len(s)-3 {
		count += checkXmas2(s, x, y, dx, 1)
	}
	return
}

const WORD string = "XMAS"

func checkXmas2(s []string, x, y, dx, dy int) int {
	if dx == 0 && dy == 0 {
		return 0
	}
	for i := 0; i < 4; i++ {
		if s[y][x] != WORD[i] {
			return 0
		}
		x += dx
		y += dy
	}
	return 1
}

func part2(s []string) (count int) {
	width := len(s[0])
	height := len(s)
	str := []byte{0, 0, 0, 0}

	for y := 1; y < height-1; y++ {
		for x := 1; x < width-1; x++ {
			if s[y][x] == 'A' {
				str[0] = s[y-1][x-1]
				str[1] = s[y-1][x+1]
				str[2] = s[y+1][x+1]
				str[3] = s[y+1][x-1]
				count += checkXMas(str)
			}
		}
	}
	return
}

func checkXMas(b []byte) int {
	i := 3
	j := 0
	for n := 0; n < 4; n++ {
		if b[i] == 'S' && b[j] == 'M' {
			break
		}
		i = j
		j += 1
	}
	if b[j%4] == 'M' && b[(j+1)%4] == 'M' && b[(j+2)%4] == 'S' && b[(j+3)%4] == 'S' {
		return 1
	}
	return 0
}