package main

import (
	"flag"
	"fmt"
	"os"
	"regexp"
	"strconv"
	"strings"
)

var (
	inputFile = flag.String("input", "input.txt", "input filename")
	nRegex    = regexp.MustCompile(`(?m)\d`)
	reMap     = map[string]string{
		"one":   "1",
		"two":   "2",
		"three": "3",
		"four":  "4",
		"five":  "5",
		"six":   "6",
		"seven": "7",
		"eight": "8",
		"nine":  "9",
	}
)

func main() {
	flag.Parse()
	input, err := os.ReadFile(*inputFile)
	if err != nil {
		panic(err)
	}

	var sum int
	for _, line := range strings.Split(string(input), "\n") {
		if strings.TrimSpace(line) == "" {
			continue
		}

		// forward-scan for spelled digits
		var forwardReplacedLine, backwardReplacedLine string
		for i := 0; i < len(line); i++ {
			forwardReplacedLine += string(line[i])

			// replace all potential spelled out digits by their non-word counterpart (e.g. "one" -> "1")
			for key, val := range reMap {
				forwardReplacedLine = strings.ReplaceAll(forwardReplacedLine, key, val)
			}
		}
		fmt.Println(forwardReplacedLine)

		// backward-scan for spelled digits
		for i := len(line) - 1; i >= 0; i-- {
			if i == len(line)-1 {
				backwardReplacedLine = string(line[i])
			} else {
				backwardReplacedLine = string(line[i]) + backwardReplacedLine
			}

			// replace all potential spelled out digits by their non-word counterpart (e.g. "one" -> "1")
			for key, val := range reMap {
				backwardReplacedLine = strings.ReplaceAll(backwardReplacedLine, key, val)
			}
		}
		fmt.Println(backwardReplacedLine)

		// find single digits in forward-replaced line
		firstMatch := nRegex.FindAllStringSubmatch(forwardReplacedLine, -1)

		// find single digits in backward-replaced line
		lastMatch := nRegex.FindAllStringSubmatch(backwardReplacedLine, -1)

		// get first match, first matchgroup (aka first digit in forwardReplacedLine)
		first := firstMatch[0][0]

		// get last match, first matchgroup (aka last digit in backwardReplacedLine)
		last := lastMatch[len(lastMatch)-1:][0][0]

		fmt.Println(first + last)

		// concatenate digits and convert the resulting string to int
		asInt, err := strconv.Atoi(first + last)
		if err != nil {
			panic(err)
		}

		sum += asInt
	}

	fmt.Println(sum)
}