package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
)

var (
	tree = "#"
	snow = "."
)

func proccessLines(path string, f func(string) (stop bool, err error)) error {
	file, err := os.Open(path)
	if err != nil {
		return err
	}
	defer file.Close()
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		stop, err := f(scanner.Text())
		if stop || err != nil {
			return err
		}
	}
	if err := scanner.Err(); err != nil {
		return err
	}
	return nil
}

type world struct {
	x, y     int
	dx, dy   int
	worldMap []string
}

func (w *world) move(dx, dy int) string {
	result := w.peek(dx, dy)
	w.x += dx
	w.y += dy
	return result
}

func (w world) peek(dx, dy int) string {
	row := w.worldMap[w.y+dy]
	return string(row[(w.x+dx)%len(row)])
}

func (w world) atEnd() bool {
	return w.y >= len(w.worldMap)-1
}

func (w *world) setSlope(dx, dy int) {
	w.dx = dx
	w.dy = dy
}

func (w *world) ski() int {
	trees := 0
	for !w.atEnd() {
		space := w.move(w.dx, w.dy)
		if space == tree {
			trees++
		}
	}
	return trees
}

func (w *world) takeLift() {
	w.x, w.y = 0, 0
}

func readMap() world {
	worldMap := []string{}
	err := proccessLines("input.txt", func(line string) (stop bool, err error) {
		worldMap = append(worldMap, line)
		return
	})
	if err != nil {
		log.Fatal(err)
	}
	return world{worldMap: worldMap}
}

func part1() {
	theWorld := readMap()
	theWorld.setSlope(3, 1)
	trees := theWorld.ski()
	fmt.Printf("Total trees: %d\n", trees)
}

func part2() {
	trees := []int{}
	theWorld := readMap()

	product := 1
	for _, slope := range [][]int{
		[]int{1, 1},
		[]int{3, 1},
		[]int{5, 1},
		[]int{7, 1},
		[]int{1, 2},
	} {
		theWorld.setSlope(slope[0], slope[1])
		count := theWorld.ski()
		product *= count
		trees = append(trees, count)
		theWorld.takeLift()
	}

	fmt.Printf("Total trees: %v, product: %d\n", trees, product)
}

func main() {
	part1()
	part2()
}