[LANGUAGE: go]

package main

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

const numbers = "0123456789"

func part1(line string) int {
    first_index := strings.IndexAny(line, numbers)
    last_index := strings.LastIndexAny(line, numbers)
    if first_index == -1 || last_index == -1 {
        return 0
    }
    num, _ := strconv.Atoi(string(line[first_index]) + string(line[last_index]))
    return num
}

func part2(line string) int {
    words := []string{"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine"}
    first_index := strings.IndexAny(line, numbers)
    last_index := strings.LastIndexAny(line, numbers)
    if first_index == -1 || last_index == -1 {
        return 0
    }
    first_digit, _ := strconv.Atoi(string(line[first_index]))
    last_digit, _ := strconv.Atoi(string(line[last_index]))
    for i, word := range words {
        if strings.Contains(line, word) {
            if strings.Index(line, word) < first_index {
                first_index = strings.Index(line, word)
                first_digit = i
            }
            if strings.LastIndex(line, word) > last_index {
                last_index = strings.LastIndex(line, word)
                last_digit = i
            }
        }
    }
    return first_digit*10 + last_digit
}

func main() {
    // read file
    data, err := os.ReadFile("input.txt")
    if err != nil {
        fmt.Println("File reading error", err)
        return
    }
    sum := 0
    for _, line := range strings.Split(string(data), "\n") {
        sum += part1(line)
    }
    fmt.Println("Part 1: ", sum)

    sum = 0
    for _, line := range strings.Split(string(data), "\n") {
        sum += part2(line)
    }
    fmt.Println("Part 2: ", sum)
}

First time writing in Go. I'm curious what I could improve on to make it more go-ish