use crate::BufMut;

use std::{cmp, io};

/// A `BufMut` adapter which implements `io::Write` for the inner value.

///

/// This struct is generally created by calling `writer()` on `BufMut`. See

/// documentation of [`writer()`](BufMut::writer) for more

/// details.

#[derive(Debug)]

pub struct Writer<B> {

    buf: B,

}

pub fn new<B>(buf: B) -> Writer<B> {

    Writer { buf }

}

impl<B: BufMut> Writer<B> {

    /// Gets a reference to the underlying `BufMut`.

    ///

    /// It is inadvisable to directly write to the underlying `BufMut`.

    ///

    /// # Examples

    ///

    /// ```rust

    /// use bytes::BufMut;

    ///

    /// let buf = Vec::with_capacity(1024).writer();

    ///

    /// assert_eq!(1024, buf.get_ref().capacity());

    /// ```

    pub fn get_ref(&self) -> &B {

        &self.buf

    }

    /// Gets a mutable reference to the underlying `BufMut`.

    ///

    /// It is inadvisable to directly write to the underlying `BufMut`.

    ///

    /// # Examples

    ///

    /// ```rust

    /// use bytes::BufMut;

    ///

    /// let mut buf = vec![].writer();

    ///

    /// buf.get_mut().reserve(1024);

    ///

    /// assert_eq!(1024, buf.get_ref().capacity());

    /// ```

    pub fn get_mut(&mut self) -> &mut B {

        &mut self.buf

    }

    /// Consumes this `Writer`, returning the underlying value.

    ///

    /// # Examples

    ///

    /// ```rust

    /// use bytes::BufMut;

    /// use std::io;

    ///

    /// let mut buf = vec![].writer();

    /// let mut src = &b"hello world"[..];

    ///

    /// io::copy(&mut src, &mut buf).unwrap();

    ///

    /// let buf = buf.into_inner();

    /// assert_eq!(*buf, b"hello world"[..]);

    /// ```

    pub fn into_inner(self) -> B {

        self.buf

    }

}

impl<B: BufMut + Sized> io::Write for Writer<B> {

    fn write(&mut self, src: &[u8]) -> io::Result<usize> {

        let n = cmp::min(self.buf.remaining_mut(), src.len());

        self.buf.put_slice(&src[..n]);

        Ok(n)

    }

    fn flush(&mut self) -> io::Result<()> {

        Ok(())

    }

}