package main

import (
	"fmt"
	"strings"

	h "git.bullercodeworks.com/brian/adventofcode/helpers"
)

func main() {
	input := h.StdinToStringSlice()
	part1(input)
	part2(input)
}

func part1(input []string) {
	field, blizzards, start, target := parseInput(input)
	fmt.Println("# Part 1")
	fmt.Println(run(field, blizzards, start, target))
}

func part2(input []string) {
	field, blizzards, start, target := parseInput(input)
	fmt.Println("# Part 2")
	fmt.Println(run(field, blizzards, start, target) +
		run(field, blizzards, target, start) +
		run(field, blizzards, start, target))
}

type Blizzard struct {
	pos, dir, wrap h.Coordinate
}

var (
	U = h.Coordinate{X: 0, Y: -1}
	D = h.Coordinate{X: 0, Y: 1}
	L = h.Coordinate{X: -1, Y: 0}
	R = h.Coordinate{X: 1, Y: 0}
)

var directions []h.Coordinate = []h.Coordinate{U, D, L, R}

func parseInput(lines []string) (field [][]rune, blizzards []Blizzard, start, target h.Coordinate) {
	start.X = strings.Index(lines[0], "E")
	if start.X == -1 {
		start.X = strings.Index(lines[0], ".")
	}
	target.Y = len(lines) - 1
	target.X = strings.Index(lines[target.Y], ".")
	for _, line := range lines {
		line = strings.TrimSpace(line)
		field = append(field, []rune(line))
	}
	for y, row := range field {
		for x, c := range row {
			switch c {
			case '^':
				blizzards = append(blizzards, Blizzard{
					h.Coordinate{X: x, Y: y}, U, h.Coordinate{X: x, Y: len(field) - 2},
				})
			case 'v':
				blizzards = append(blizzards, Blizzard{
					h.Coordinate{X: x, Y: y}, D, h.Coordinate{X: x, Y: 1},
				})
			case '<':
				blizzards = append(blizzards, Blizzard{
					h.Coordinate{X: x, Y: y}, L, h.Coordinate{X: len(field[0]) - 2, Y: y},
				})
			case '>':
				blizzards = append(blizzards, Blizzard{
					h.Coordinate{X: x, Y: y}, R, h.Coordinate{X: 1, Y: y},
				})
			}
		}
	}
	return
}

func valid(field [][]rune, pos h.Coordinate) bool {
	return pos.X >= 0 && pos.X < len(field[0]) && pos.Y >= 0 && pos.Y < len(field)
}

func run(field [][]rune, blizzards []Blizzard, start, target h.Coordinate) int {
	minutes := 0
	currentStep := make(map[h.Coordinate]bool)
	currentStep[start] = true

	for !currentStep[target] {
		//update blizzards
		whereBlizzards := make(map[h.Coordinate]bool)
		for i, b := range blizzards {
			bb := b.pos.Add(b.dir)
			if valid(field, bb) {
				if field[bb.Y][bb.X] == '#' {
					blizzards[i].pos = b.wrap
				} else {
					blizzards[i].pos = bb
				}
			}
			whereBlizzards[blizzards[i].pos] = true
		}

		//find new steps
		newStep := make(map[h.Coordinate]bool)
		for pos := range currentStep {
			if !(whereBlizzards[pos]) {
				newStep[pos] = true
			}
			for _, d := range directions {
				n := pos.Add(d)
				if valid(field, n) && field[n.Y][n.X] != '#' && !whereBlizzards[n] {
					newStep[n] = true
				}
			}
		}
		currentStep = newStep
		minutes++
	}

	return minutes
}