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// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// <https://github.com/rust-lang/rust/blob/HEAD/COPYRIGHT>.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use std::cmp;
use std::io;
use std::io::prelude::*;
use std::mem;

pub struct BufReader<R> {
    inner: R,
    buf: Box<[u8]>,
    pos: usize,
    cap: usize,
}

impl<R> ::std::fmt::Debug for BufReader<R>
where
    R: ::std::fmt::Debug,
{
    fn fmt(&self, fmt: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
        fmt.debug_struct("BufReader")
            .field("reader", &self.inner)
            .field(
                "buffer",
                &format_args!("{}/{}", self.cap - self.pos, self.buf.len()),
            )
            .finish()
    }
}

impl<R: Read> BufReader<R> {
    pub fn new(inner: R) -> BufReader<R> {
        BufReader::with_buf(vec![0; 32 * 1024], inner)
    }

    pub fn with_buf(buf: Vec<u8>, inner: R) -> BufReader<R> {
        BufReader {
            inner,
            buf: buf.into_boxed_slice(),
            pos: 0,
            cap: 0,
        }
    }
}

impl<R> BufReader<R> {
    pub fn get_ref(&self) -> &R {
        &self.inner
    }

    pub fn get_mut(&mut self) -> &mut R {
        &mut self.inner
    }

    pub fn into_inner(self) -> R {
        self.inner
    }

    pub fn reset(&mut self, inner: R) -> R {
        self.pos = 0;
        self.cap = 0;
        mem::replace(&mut self.inner, inner)
    }
}

impl<R: Read> Read for BufReader<R> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        // If we don't have any buffered data and we're doing a massive read
        // (larger than our internal buffer), bypass our internal buffer
        // entirely.
        if self.pos == self.cap && buf.len() >= self.buf.len() {
            return self.inner.read(buf);
        }
        let nread = {
            let mut rem = self.fill_buf()?;
            rem.read(buf)?
        };
        self.consume(nread);
        Ok(nread)
    }
}

impl<R: Read> BufRead for BufReader<R> {
    fn fill_buf(&mut self) -> io::Result<&[u8]> {
        // If we've reached the end of our internal buffer then we need to fetch
        // some more data from the underlying reader.
        if self.pos == self.cap {
            self.cap = self.inner.read(&mut self.buf)?;
            self.pos = 0;
        }
        Ok(&self.buf[self.pos..self.cap])
    }

    fn consume(&mut self, amt: usize) {
        self.pos = cmp::min(self.pos + amt, self.cap);
    }
}