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use std::env;
use std::fs;
use std::collections::HashMap;
use std::error::Error;

fn main() {
    let args: Vec<String> = env::args().collect();
    if args.len() < 2 {
        eprintln!("Usage: {} <filename>", args[0]);
        std::process::exit(1);
    }
    let filename = &args[1];

    match read_and_process_file(filename) {
        Ok(word_count) => {
            for (word, count) in word_count {
                println!("{}: {}", word, count);
            }
        }
        Err(e) => {
            eprintln!("Error processing file: {}", e);
        }
    }
}

fn read_and_process_file(filename: &str) -> Result<HashMap<String, u32>, Box<dyn Error>> {
    let contents = fs::read_to_string(filename)?;
    let mut word_count = HashMap::new();

    for word in contents.split_whitespace() {
        let count = word_count.entry(word.to_lowercase()).or_insert(0);
        *count += 1;
    }

    Ok(word_count)
}