use regex::Regex;
use std::collections::HashMap;
use std::fs::File;
use std::io::{self, BufRead};
use std::path::Path;

fn main() -> io::Result<()> {
    // File must exist in the current path
    let mut result = 0;
    if let Ok(lines) = read_lines("./src/input") {
        for line in lines.flatten() {
            print!("{} -> ", line);

            // No need for .as_str(), just pass &line
            let mut replaced_line = replace_written_digits(&line);
            replaced_line = replace_written_digits(&replaced_line);
            println!("{}", replaced_line);
            if let Some(value) = extract_digit_pair_sum(&replaced_line) {
                println!("Current result: {} + {} = {}", result, value, result + value);
                result += value;
            }
        }
    }

    println!("Final result: {}", result);

    Ok(())
}

fn replace_written_digits<T: AsRef<str>>(input: T) -> String {
    // Create a map of written digits to their numeric counterparts
    let digit_map = HashMap::from([
        ("one", "1ne"),
        ("two", "2wo"),
        ("three", "3hree"),
        ("four", "4our"),
        ("five", "5ive"),
        ("six", "6ix"),
        ("seven", "7even"),
        ("eight", "8ight"),
        ("nine", "9ine"),
    ]);

    // Create a regex that matches the written digits
    let re = Regex::new(r"(?:one|two|three|four|five|six|seven|eight|nine)").unwrap();

    // Replace all occurrences of written digits with their numeric counterparts
    re.replace_all(input.as_ref(), |caps: &regex::Captures| {
        // Access the full match (use caps.get(0) instead of caps[1])
        let matched_word = caps.get(0).unwrap().as_str();
        digit_map.get(matched_word).unwrap().to_string()
    }).to_string()
}

// Extracts first and last digits from a line, forms a number, and returns the sum
fn extract_digit_pair_sum(line: &str) -> Option<i32> {
    let first_digit = get_first_digit(line)?;
    let last_digit = get_last_digit(line)?;

    let digit_str = format!("{}{}", first_digit, last_digit);
    digit_str.parse::<i32>().ok()
}

// Helper function to get the first digit in the string
fn get_first_digit(s: &str) -> Option<char> {
    s.chars().find(|&c| c.is_digit(10))
}

// Helper function to get the last digit in the string
fn get_last_digit(s: &str) -> Option<char> {
    s.chars().rev().find(|&c| c.is_digit(10))
}

// Returns an Iterator over the lines in the file
fn read_lines<P>(filename: P) -> io::Result<io::Lines<io::BufReader<File>>>
where
    P: AsRef<Path>,
{
    let file = File::open(filename)?;
    Ok(io::BufReader::new(file).lines())
}