//! Utilities for working with buffers.
//!
//! A buffer is any structure that contains a sequence of bytes. The bytes may
//! or may not be stored in contiguous memory. This module contains traits used
//! to abstract over buffers as well as utilities for working with buffer types.
//!
//! # `Buf`, `BufMut`
//!
//! These are the two foundational traits for abstractly working with buffers.
//! They can be thought as iterators for byte structures. They offer additional
//! performance over `Iterator` by providing an API optimized for byte slices.
//!
//! See [`Buf`] and [`BufMut`] for more details.
//!
//! [rope]: https://en.wikipedia.org/wiki/Rope_(data_structure)
//! [`Buf`]: trait.Buf.html
//! [`BufMut`]: trait.BufMut.html

use std::{cmp, io, usize};

mod buf;
mod buf_mut;
mod from_buf;
mod into_buf;
mod iter;
mod reader;
mod source;
mod take;
mod writer;

pub use self::buf::Buf;
pub use self::buf_mut::BufMut;
pub use self::from_buf::FromBuf;
pub use self::into_buf::IntoBuf;
pub use self::iter::Iter;
pub use self::reader::Reader;
pub use self::source::Source;
pub use self::take::Take;
pub use self::writer::Writer;

/*
 *
 * ===== Buf impls =====
 *
 */

impl<'a, T: Buf> Buf for &'a mut T {
    fn remaining(&self) -> usize {
        (**self).remaining()
    }

    fn bytes(&self) -> &[u8] {
        (**self).bytes()
    }

    fn advance(&mut self, cnt: usize) {
        (**self).advance(cnt)
    }
}

impl<'a, T: BufMut> BufMut for &'a mut T {
    fn remaining_mut(&self) -> usize {
        (**self).remaining_mut()
    }

    unsafe fn bytes_mut(&mut self) -> &mut [u8] {
        (**self).bytes_mut()
    }

    unsafe fn advance_mut(&mut self, cnt: usize) {
        (**self).advance_mut(cnt)
    }
}

impl<T: AsRef<[u8]>> Buf for io::Cursor<T> {
    fn remaining(&self) -> usize {
        let len = self.get_ref().as_ref().len();
        let pos = self.position();

        if pos >= len as u64 {
            return 0;
        }

        len - pos as usize
    }

    fn bytes(&self) -> &[u8] {
        let pos = self.position() as usize;
        &(self.get_ref().as_ref())[pos..]
    }

    fn advance(&mut self, cnt: usize) {
        let pos = self.position() as usize;
        let pos = cmp::min(self.get_ref().as_ref().len(), pos + cnt);
        self.set_position(pos as u64);
    }
}

impl<T: AsMut<[u8]> + AsRef<[u8]>> BufMut for io::Cursor<T> {
    fn remaining_mut(&self) -> usize {
        self.remaining()
    }

    /// Advance the internal cursor of the BufMut
    unsafe fn advance_mut(&mut self, cnt: usize) {
        let pos = self.position() as usize;
        let pos = cmp::min(self.get_mut().as_mut().len(), pos + cnt);
        self.set_position(pos as u64);
    }

    /// Returns a mutable slice starting at the current BufMut position and of
    /// length between 0 and `BufMut::remaining()`.
    ///
    /// The returned byte slice may represent uninitialized memory.
    unsafe fn bytes_mut(&mut self) -> &mut [u8] {
        let pos = self.position() as usize;
        &mut (self.get_mut().as_mut())[pos..]
    }
}

impl BufMut for Vec<u8> {
    fn remaining_mut(&self) -> usize {
        usize::MAX - self.len()
    }

    unsafe fn advance_mut(&mut self, cnt: usize) {
        let len = self.len() + cnt;

        if len > self.capacity() {
            // Reserve additional
            // TODO: Should this case panic?
            let cap = self.capacity();
            self.reserve(cap - len);
        }

        self.set_len(len);
    }

    unsafe fn bytes_mut(&mut self) -> &mut [u8] {
        use std::slice;

        if self.capacity() == self.len() {
            self.reserve(64); // Grow the vec
        }

        let cap = self.capacity();
        let len = self.len();

        let ptr = self.as_mut_ptr();
        &mut slice::from_raw_parts_mut(ptr, cap)[len..]
    }
}