use std::path::Path;
use std::fs::read_to_string;


pub fn head(path: &Path, n: usize) -> Vec<String> {
    let mut result = Vec::new();

    for line in read_to_string(path).unwrap().lines() {
        result.push(line.to_string())
    }

    let len = result.len();
    if len < n {
        panic!("file too short!");
    }

    result[0..n].to_vec()
}

pub fn tail(path: &Path, n: usize) -> Vec<String> {
    let mut result = Vec::new();

    for line in read_to_string(path).unwrap().lines() {
        result.push(line.to_string())
    }

    let len = result.len();
    if len < n {
        panic!("file too short!");
    }

    result[len-n..].to_vec()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_head() {
        let path = Path::new("test_data/file.txt");
        assert_eq!(head(path, 2), vec!["aaa", "bbb"]);
    }

    #[test]
    fn test_tail() {
        let path = Path::new("test_data/file.txt");
        assert_eq!(tail(path, 2), vec!["bbb", "ccc"]);
    }
}