package main

import (
	"bufio"
	"log"
	"math"
	"os"
)

type Position struct {
	X int
	Y int
}

func main() {
	file, err := os.Open("input.txt")
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()

	t2 := make([]string, 0)
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		t2 = append(t2, scanner.Text())
	}

	field, asteroids := ParseStringSliceToField(t2)

	SolvePzl1(field, asteroids)
}

func SolvePzl1(field [][]int, asteroids []Position) {
	highestFoundAstros := math.MinInt32
	pos := Position{}

	for _, astro := range asteroids {
		sum := CountAsteroidsFromPosition(field, astro.X, astro.Y)
		if highestFoundAstros < sum {
			highestFoundAstros = sum
			pos = astro
		}
	}

	log.Printf("Part1: Found %d Astros at Position(%d,%d) from %d Astros", highestFoundAstros, pos.X, pos.Y, len(asteroids))
}

func ParseStringSliceToField(view []string) (field [][]int, asteroids []Position) {
	field = make([][]int, 0)
	asteroids = make([]Position, 0)

	x, y := 0, 0

	for i, line := range view {
		x = 0
		field = append(field, make([]int, 0))
		for j := 0; j < len(line); j++ {
			if "#" == string(line[j]) {
				field[i] = append(field[i], 0)
				asteroids = append(asteroids, Position{X: x, Y: y})
			} else {
				field[i] = append(field[i], -1)
			}
			x++
		}
		y++
	}
	return
}

func CountAsteroidsFromPosition(field [][]int, posX, posY int) (sum int) {
	duplicate := Copy2DSlice(field)
	steps := make(map[int]int, 0)

	for y := 0; y < len(duplicate); y++ {
		for x := 0; x < len(duplicate[y]); x++ {
			if x == posX && y == posY {
				continue
			}

			stepX := x - posX
			stepY := y - posY

			gcd := GCD(stepY, stepX)

			if gcd == 0 {
				if stepX > 0 {
					stepX = 1
				} else if stepX < 0 {
					stepX = -1
				} else if stepY > 0 {
					stepY = 1
				} else if stepY < 0 {
					stepY = -1
				}
			} else {
				stepX, stepY = stepX/gcd, stepY/gcd
			}

			if v, ok := steps[stepX]; ok && v == stepY {
				continue
			}
			steps[stepX] = stepY

			curX, curY := posX, posY
			found := false
			for true {
				curX += stepX
				curY += stepY

				if curY < 0 || curX < 0 || curY >= len(duplicate) || curX >= len(duplicate[curY]) {
					break
				}

				if duplicate[curY][curX] >= 0 {
					//log.Printf("(%d,%d) from (%d,%d)", curX, curY, stepX, stepY)
					if !found {
						found = true
						sum++
					}
					duplicate[curY][curX] = -2
				}
			}
		}
	}

	return
}

func Copy2DSlice(matrix [][]int) (duplicate [][]int) {
	duplicate = make([][]int, len(matrix))
	for i := range matrix {
		duplicate[i] = make([]int, len(matrix[i]))
		copy(duplicate[i], matrix[i])
	}
	return
}

// greatest common divisor (GCD) via Euclidean algorithm
func GCD(a, b int) int {
	for b != 0 {
		t := b
		b = a % b
		a = t
	}

	if a < 0 {
		a = a * -1
	}

	return a
}