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/*
==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--

Bi

Copyright (C) 2019, 2021-2022, 2024  Anonymous

There are several releases over multiple years,
they are listed as ranges, such as: "2021-2022".

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>.

::--::--::--::--::--::--::--::--::--::--::--::--::--::--::--::--
*/

use {
    std::{
        fs::File,
        io::{self, BufReader, Read, Stdin},
        path::Path,
    },
    crate::IoResult,
};

#[cfg(test)]
mod tests;

/// # Limit
///
/// This struct can be used for limiting data read from some source.
#[derive(Debug)]
pub struct Limit<R> where R: Read {
    inner: R,
    read: u64,
    limit: u64,
}

impl<R> Limit<R> where R: Read {

    /// # Makes new object
    pub fn new(inner: R, limit: u64) -> Self {
        Self {
            inner,
            read: u64::MIN,
            limit,
        }
    }

}

impl Limit<BufReader<File>> {

    /// # Opens a file for reading with a limit
    ///
    /// The file will be wrapped inside a [`BufReader`][struct:std/io/BufReader].
    ///
    /// [struct:std/io/BufReader]: https://doc.rust-lang.org/std/io/struct.BufReader.html
    pub fn open_file<P>(path: P, limit: u64) -> IoResult<Self> where P: AsRef<Path> {
        let path = path.as_ref();

        match path.metadata()?.len() {
            size => if size > limit {
                return Err(err!("File too large: {size} (limit: {limit})"));
            },
        };

        Ok(Self::new(BufReader::new(File::open(path)?), limit))
    }

}

impl Limit<Stdin> {

    /// # Makes new object from standard input
    pub fn stdin(limit: u64) -> IoResult<Self> {
        Ok(Self::new(io::stdin(), limit))
    }

}

impl<R> Read for Limit<R> where R: Read {

    fn read(&mut self, buf: &mut [u8]) -> IoResult<usize> {
        macro_rules! check { () => {
            if self.read > self.limit {
                return Err(err!("Limit: {limit}, already read: {read}", limit=self.limit, read=self.read));
            }
        }}

        check!();
        let result = self.inner.read(buf)?;

        match u64::try_from(result).map_err(|_| err!("Cannot convert {result} into u64"))?.checked_add(self.read) {
            None => return Err(err!("Failed: {read} + {result}", read=self.read)),
            Some(read) => self.read = read,
        };

        check!();
        Ok(result)
    }

}