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//! # Input and output manager

use std::{io, str};

/// Scanner is a struct that can be used to parse input from a reader.
///
/// # Examples
/// ```
/// use cp_template::iom::Scanner;
/// use std::io;
///
/// fn main() {
///     let mut scan = Scanner::new(io::stdin().lock());
///     let mut out = io::BufWriter::new(io::stdout().lock());
///     solve(&mut scan, &mut out);
/// }
///
/// fn solve<R: io::BufRead, W: io::Write>(scan: &mut Scanner<R>, out: &mut W) {
///     let n: usize = scan.tok();
///     let v: Vec<i32> = (0..n).map(|_| scan.tok()).collect();
///     writeln!(out, "{} {v:?}", n).ok();
/// }
/// ```
/// ```
/// use cp_template::iom::Scanner;
/// use std::io;
///
/// fn main() {
///     let mut scan = read_file("in.txt").unwrap();
///     let mut out = writer_file("out.txt").unwrap();
///     solve(&mut scan, &mut out);
/// }
///
/// fn solve<R: io::BufRead, W: io::Write>(scan: &mut Scanner<R>, out: &mut W) {
///     let n: usize = scan.tok();
///     let v: Vec<i32> = (0..n).map(|_| scan.tok()).collect();
///     writeln!(out, "{} {v:?}", n).ok();
/// }
/// ```
pub struct Scanner<R> {
    reader: R,
    buf_str: Vec<u8>,
    buf_iter: str::SplitAsciiWhitespace<'static>,
}

impl<R: io::BufRead> Scanner<R> {
    /// Creates a new Scanner.
    /// # Examples
    /// ```
    /// let mut scan = Scanner::new(std::io::stdin().lock());
    /// ```
    /// ```
    /// let file = std::fs::File::open(filename)?;
    /// Scanner::new(io::BufReader::new(file))
    /// ```
    pub fn new(reader: R) -> Self {
        Self {
            reader,
            buf_str: vec![],
            buf_iter: "".split_ascii_whitespace(),
        }
    }

    /// Reads a token.
    /// # Panics
    /// Panics if the token can't be parsed or the input is empty.
    /// # Examples
    /// ```
    /// let mut scan = Scanner::new(std::io::stdin().lock());
    /// let n: i32 = scan.tok();
    /// ```
    /// ```
    /// let mut scan = Scanner::new(std::io::stdin().lock());
    /// let n = scan.tok::<i32>();
    /// ```
    pub fn tok<T: str::FromStr>(&mut self) -> T {
        loop {
            if let Some(token) = self.buf_iter.next() {
                return token.parse().ok().expect("Failed parse");
            }
            self.buf_str.clear();
            self.reader
                .read_until(b'\n', &mut self.buf_str)
                .expect("Failed read");
            self.buf_iter = unsafe {
                let slice = str::from_utf8_unchecked(&self.buf_str);
                std::mem::transmute(slice.split_ascii_whitespace())
            }
        }
    }
}

/// Creates a Scanner from a file
/// # Examples
/// ```
/// let mut scan = file_reader("in.txt").unwrap();
/// let n: i32 = scan.tok();
/// ```
pub fn file_reader(filename: &str) -> io::Result<Scanner<io::BufReader<std::fs::File>>> {
    let file = std::fs::File::open(filename)?;
    Ok(Scanner::new(io::BufReader::new(file)))
}

/// Creates a BufWriter from a file
/// # Examples
/// ```
/// let n = 42;
/// let mut out = file_writer("out.txt").unwrap();
/// writeln!(out, "{}", n).ok();
/// ```
pub fn file_writer(filename: &str) -> io::Result<io::BufWriter<std::fs::File>> {
    let file = std::fs::File::create(filename)?;
    Ok(io::BufWriter::new(file))
}