package main

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

func readInput(file *os.File) []string {
	scanner := bufio.NewScanner(file)
	var lines []string

	for scanner.Scan() {
		line := scanner.Text()
		if line == "" {
			break
		}

		lines = append(lines, line)
	}

	return lines
}

const firstDigit = 48
const lastDigit = 57

func isDigit(b byte) bool {
	return firstDigit <= b && b <= lastDigit
}

func isSymbol(b byte) bool {
	return !isDigit(b) && b != '.'
}

func symbolNear(lines []string, height int, width int, y int, start int, end int) bool {
	i := start - 1
	if i < 0 {
		i = start
	}

	if end >= width {
		end = width - 1
	}

	canGoUp := y-1 >= 0
	canGoDown := y+1 < height

	for ; i <= end; i++ {
		if isSymbol(lines[y][i]) {
			return true
		}

		if canGoUp && isSymbol(lines[y-1][i]) {
			return true
		}

		if canGoDown && isSymbol(lines[y+1][i]) {
			return true
		}
	}

	return false
}

func part1(lines []string) int {
	var result int
	height := len(lines)
	width := len(lines[0])
	edge := width - 1
	for i := range lines {
		var start, end int
		gotNumber := false
		tryRead := false
		for j := range lines[i] {
			if isDigit(lines[i][j]) {
				if !gotNumber {
					start = j
					gotNumber = true
				}

				if j == edge {
					end = j + 1
					tryRead = true
				}
			} else {
				if !gotNumber {
					continue
				}

				end = j
				gotNumber = false
				tryRead = true
			}

			if tryRead {
				if symbolNear(lines, height, width, i, start, end) {
					var d int
					n, err := fmt.Sscanf(lines[i][start:end], "%d", &d)
					if n != 1 || err != nil {
						log.Fatalf("Wrong input: %s\n%s", lines[i][start:end], err)
					}

					result += d
				}

				tryRead = false
			}

		}
	}

	return result
}

func main() {
	if len(os.Args) < 2 {
		log.Fatal("You need to specify a file!")
	}

	filePath := os.Args[1]
	file, err := os.Open(filePath)
	if err != nil {
		log.Fatalf("Failed to open %s!\n", filePath)

	}

	lines := readInput(file)
	fmt.Println("Part1:", part1(lines))
}