rustlings/solutions/24_file_io/file_io2.rs

use std::fs;
use std::io::{BufRead, BufReader, BufWriter, Write};
use std::path::Path;

const TEST_INPUT_FILE_NAME: &str = "MultiLineTextFile.txt";
const TEST_OUTPUT_FILE_NAME: &str = "MultiLineOutputFile.txt";
const SAMPLE_TEXT: &str = "This is the first line of the text.
        This is the second line.
        And this is the third and the last line.";

fn main() -> Result<(), std::io::Error> {
    create_required_files()?;

    let input_file = fs::File::open(TEST_INPUT_FILE_NAME).inspect_err(|err| {
        eprintln!("{} file open error {:?}", TEST_INPUT_FILE_NAME, err);
    })?;

    let buffered_input_file = BufReader::new(input_file);

    let output_file = fs::File::create(TEST_OUTPUT_FILE_NAME).inspect_err(|err| {
        eprintln!("{} file open error {:?}", TEST_OUTPUT_FILE_NAME, err);
    })?;

    let mut buffered_file_writer = BufWriter::new(output_file);

    let mut lines_processed = 0;

    for (index, line) in buffered_input_file.lines().enumerate() {
        let line = line.inspect_err(|err| {
            eprintln!("{} line parse error {:?}", TEST_INPUT_FILE_NAME, err);
        })?;

        let line_number = index + 1;
        writeln!(buffered_file_writer, "Line {} : {}", line_number, line).inspect_err(|err| {
            eprintln!("{} line write error {:?}", TEST_INPUT_FILE_NAME, err);
        })?;

        lines_processed = line_number;
    }

    println!("{} : lines processed", lines_processed);
    file_cleanup()
}

fn create_required_files() -> Result<(), std::io::Error> {
    let file_path = Path::new(TEST_INPUT_FILE_NAME);

    if !file_path.exists() {
        fs::write(file_path, SAMPLE_TEXT).inspect_err(|err| {
            eprintln!("Couldn't create the test file : {}", err);
        })?;
    }

    Ok(())
}

fn file_cleanup() -> Result<(), std::io::Error> {
    let file_names = vec![TEST_INPUT_FILE_NAME, TEST_OUTPUT_FILE_NAME];

    for file_name in file_names {
        let file_path = Path::new(file_name);

        if file_path.exists() {
            fs::remove_file(file_path).inspect(|_| {
                println!("Test file {} removed", file_name);
            })?;
        } else {
            println!("No cleanup necessary since {} not exist.", file_name);
        }
    }

    Ok(())
}