//! Circular, a stream abstraction designed for use with nom
//!
//! Circular provides a `Buffer` type that wraps a `Vec<u8>` with a position
//! and end. Compared to a stream abstraction that would use `std::io::Read`,
//! it separates the reading and consuming phases. `Read` is designed to write
//! the data in a mutable slice and consume it from the stream as it does that.
//!
//! When used in streaming mode, nom will try to parse a slice, then tell you
//! how much it consumed. So you don't know how much data was actually used
//! until the parser returns. `Circular::Buffer` exposes a `data()` method
//! that gives an immutable slice of all the currently readable data,
//! and a `consume()` method to advance the position in the stream.
//! The `space()` and `fill()` methods are the write counterparts to those methods.
//!
//! ```
//! extern crate circular;
//!
//! use circular::Buffer;
//! use std::io::Write;
//!
//! fn main() {
//!
//!   // allocate a new Buffer
//!   let mut b = Buffer::with_capacity(10);
//!   assert_eq!(b.available_data(), 0);
//!   assert_eq!(b.available_space(), 10);
//!
//!   let res = b.write(&b"abcd"[..]);
//!   assert_eq!(res.ok(), Some(4));
//!   assert_eq!(b.available_data(), 4);
//!   assert_eq!(b.available_space(), 6);
//!
//!   //the 4 bytes we wrote are immediately available and usable for parsing
//!   assert_eq!(b.data(), &b"abcd"[..]);
//!
//!   // this will advance the position from 0 to 2. it does not modify the underlying Vec
//!   b.consume(2);
//!   assert_eq!(b.available_data(), 2);
//!   assert_eq!(b.available_space(), 6);
//!   assert_eq!(b.data(), &b"cd"[..]);
//!
//!   // shift moves the available data at the beginning of the buffer.
//!   // the position is now 0
//!   b.shift();
//!   assert_eq!(b.available_data(), 2);
//!   assert_eq!(b.available_space(), 8);
//!   assert_eq!(b.data(), &b"cd"[..]);
//! }
//!
use std::io::{self, Read, Write};
use std::iter::repeat;
use std::{cmp, ptr};

extern crate bytes;
use bytes::BufMut;

/// the Buffer contains the underlying memory and data positions
///
/// In all cases, `0 ≤ position ≤ end ≤ capacity` should be true
#[derive(Debug, PartialEq, Clone)]
pub struct Buffer {
    /// the Vec containing the data
    memory: Vec<u8>,
    /// the current capacity of the Buffer
    capacity: usize,
    /// the current beginning of the available data
    position: usize,
    /// the current end of the available data
    /// and beginning of the available space
    end: usize,
}

impl Buffer {
    /// allocates a new buffer of maximum size `capacity`
    pub fn with_capacity(capacity: usize) -> Buffer {
        let mut v = Vec::with_capacity(capacity);
        v.extend(repeat(0).take(capacity));
        Buffer {
            memory: v,
            capacity: capacity,
            position: 0,
            end: 0,
        }
    }

    /// allocates a new buffer containing the slice `data`
    ///
    /// the buffer starts full, its available data size is exactly `data.len()`
    pub fn from_slice(data: &[u8]) -> Buffer {
        Buffer {
            memory: Vec::from(data),
            capacity: data.len(),
            position: 0,
            end: data.len(),
        }
    }

    /// increases the size of the buffer
    ///
    /// this does nothing if the buffer is already large enough
    pub fn grow(&mut self, new_size: usize) -> bool {
        if self.capacity >= new_size {
            return false;
        }

        self.memory.resize(new_size, 0);
        self.capacity = new_size;
        true
    }

    /// returns how much data can be read from the buffer
    pub fn available_data(&self) -> usize {
        self.end - self.position
    }

    /// returns how much free space is available to write to
    pub fn available_space(&self) -> usize {
        self.capacity - self.end
    }

    /// returns the underlying vector's size
    pub fn capacity(&self) -> usize {
        self.capacity
    }

    /// returns true if there is no more data to read
    pub fn empty(&self) -> bool {
        self.position == self.end
    }

    /// advances the position tracker
    ///
    /// if the position gets past the buffer's half,
    /// this will call `shift()` to move the remaining data
    /// to the beginning of the buffer
    pub fn consume(&mut self, count: usize) -> usize {
        let cnt = cmp::min(count, self.available_data());
        self.position += cnt;
        if self.position > self.capacity / 2 {
            //trace!("consume shift: pos {}, end {}", self.position, self.end);
            self.shift();
        }
        cnt
    }

    /// advances the position tracker
    ///
    /// This method is similar to `consume()` but will not move data
    /// to the beginning of the buffer
    pub fn consume_noshift(&mut self, count: usize) -> usize {
        let cnt = cmp::min(count, self.available_data());
        self.position += cnt;
        cnt
    }

    /// after having written data to the buffer, use this function
    /// to indicate how many bytes were written
    ///
    /// if there is not enough available space, this function can call
    /// `shift()` to move the remaining data to the beginning of the
    /// buffer
    pub fn fill(&mut self, count: usize) -> usize {
        let cnt = cmp::min(count, self.available_space());
        self.end += cnt;
        if self.available_space() < self.available_data() + cnt {
            //trace!("fill shift: pos {}, end {}", self.position, self.end);
            self.shift();
        }

        cnt
    }

    /// Get the current position
    ///
    /// # Examples
    /// ```
    /// use circular::Buffer;
    /// use std::io::{Read,Write};
    ///
    /// let mut output = [0;5];
    ///
    /// let mut b = Buffer::with_capacity(10);
    ///
    /// let res = b.write(&b"abcdefgh"[..]);
    ///
    /// b.read(&mut output);
    ///
    /// // Position must be 5
    /// assert_eq!(b.position(), 5);
    /// assert_eq!(b.available_data(), 3);
    /// ```
    pub fn position(&self) -> usize {
        self.position
    }

    /// moves the position and end trackers to the beginning
    /// this function does not modify the data
    pub fn reset(&mut self) {
        self.position = 0;
        self.end = 0;
    }

    /// returns a slice with all the available data
    pub fn data(&self) -> &[u8] {
        &self.memory[self.position..self.end]
    }

    /// returns a mutable slice with all the available space to
    /// write to
    pub fn space(&mut self) -> &mut [u8] {
        &mut self.memory[self.end..self.capacity]
    }

    /// moves the data at the beginning of the buffer
    ///
    /// if the position was more than 0, it is now 0
    pub fn shift(&mut self) {
        if self.position > 0 {
            unsafe {
                let length = self.end - self.position;
                ptr::copy(
                    (&self.memory[self.position..self.end]).as_ptr(),
                    (&mut self.memory[..length]).as_mut_ptr(),
                    length,
                );
                self.position = 0;
                self.end = length;
            }
        }
    }

    //FIXME: this should probably be rewritten, and tested extensively
    #[doc(hidden)]
    pub fn delete_slice(&mut self, start: usize, length: usize) -> Option<usize> {
        if start + length >= self.available_data() {
            return None;
        }

        unsafe {
            let begin = self.position + start;
            let next_end = self.end - length;
            ptr::copy(
                (&self.memory[begin + length..self.end]).as_ptr(),
                (&mut self.memory[begin..next_end]).as_mut_ptr(),
                self.end - (begin + length),
            );
            self.end = next_end;
        }
        Some(self.available_data())
    }

    //FIXME: this should probably be rewritten, and tested extensively
    #[doc(hidden)]
    pub fn replace_slice(&mut self, data: &[u8], start: usize, length: usize) -> Option<usize> {
        let data_len = data.len();
        if start + length > self.available_data()
            || self.position + start + data_len > self.capacity
        {
            return None;
        }

        unsafe {
            let begin = self.position + start;
            let slice_end = begin + data_len;
            // we reduced the data size
            if data_len < length {
                ptr::copy(
                    data.as_ptr(),
                    (&mut self.memory[begin..slice_end]).as_mut_ptr(),
                    data_len,
                );

                ptr::copy(
                    (&self.memory[start + length..self.end]).as_ptr(),
                    (&mut self.memory[slice_end..]).as_mut_ptr(),
                    self.end - (start + length),
                );
                self.end = self.end - (length - data_len);

            // we put more data in the buffer
            } else {
                ptr::copy(
                    (&self.memory[start + length..self.end]).as_ptr(),
                    (&mut self.memory[start + data_len..]).as_mut_ptr(),
                    self.end - (start + length),
                );
                ptr::copy(
                    data.as_ptr(),
                    (&mut self.memory[begin..slice_end]).as_mut_ptr(),
                    data_len,
                );
                self.end = self.end + data_len - length;
            }
        }
        Some(self.available_data())
    }

    //FIXME: this should probably be rewritten, and tested extensively
    #[doc(hidden)]
    pub fn insert_slice(&mut self, data: &[u8], start: usize) -> Option<usize> {
        let data_len = data.len();
        if start > self.available_data() || self.position + self.end + data_len > self.capacity {
            return None;
        }

        unsafe {
            let begin = self.position + start;
            let slice_end = begin + data_len;
            ptr::copy(
                (&self.memory[start..self.end]).as_ptr(),
                (&mut self.memory[start + data_len..]).as_mut_ptr(),
                self.end - start,
            );
            ptr::copy(
                data.as_ptr(),
                (&mut self.memory[begin..slice_end]).as_mut_ptr(),
                data_len,
            );
            self.end = self.end + data_len;
        }
        Some(self.available_data())
    }
}

impl Write for Buffer {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        match self.space().write(buf) {
            Ok(size) => {
                self.fill(size);
                Ok(size)
            }
            err => err,
        }
    }

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

impl Read for Buffer {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let len = cmp::min(self.available_data(), buf.len());
        unsafe {
            ptr::copy(
                (&self.memory[self.position..self.position + len]).as_ptr(),
                buf.as_mut_ptr(),
                len,
            );
            self.position += len;
        }
        Ok(len)
    }
}

unsafe impl BufMut for Buffer {
    fn remaining_mut(&self) -> usize {
        self.available_space()
    }

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

    fn chunk_mut(&mut self) -> &mut bytes::buf::UninitSlice {
        self.space().into()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io::Write;

    #[test]
    fn fill_and_consume() {
        let mut b = Buffer::with_capacity(10);
        assert_eq!(b.available_data(), 0);
        assert_eq!(b.available_space(), 10);
        let res = b.write(&b"abcd"[..]);
        assert_eq!(res.ok(), Some(4));
        assert_eq!(b.available_data(), 4);
        assert_eq!(b.available_space(), 6);

        assert_eq!(b.data(), &b"abcd"[..]);

        b.consume(2);
        assert_eq!(b.available_data(), 2);
        assert_eq!(b.available_space(), 6);
        assert_eq!(b.data(), &b"cd"[..]);

        b.shift();
        assert_eq!(b.available_data(), 2);
        assert_eq!(b.available_space(), 8);
        assert_eq!(b.data(), &b"cd"[..]);

        assert_eq!(b.write(&b"efghijklmnop"[..]).ok(), Some(8));
        assert_eq!(b.available_data(), 10);
        assert_eq!(b.available_space(), 0);
        assert_eq!(b.data(), &b"cdefghijkl"[..]);
        b.shift();
        assert_eq!(b.available_data(), 10);
        assert_eq!(b.available_space(), 0);
        assert_eq!(b.data(), &b"cdefghijkl"[..]);
    }

    #[test]
    fn delete() {
        let mut b = Buffer::with_capacity(10);
        let _ = b.write(&b"abcdefgh"[..]);
        assert_eq!(b.available_data(), 8);
        assert_eq!(b.available_space(), 2);

        assert_eq!(b.delete_slice(2, 3), Some(5));
        assert_eq!(b.available_data(), 5);
        assert_eq!(b.available_space(), 5);
        assert_eq!(b.data(), &b"abfgh"[..]);

        assert_eq!(b.delete_slice(5, 2), None);
        assert_eq!(b.delete_slice(4, 2), None);
    }

    #[test]
    fn replace() {
        let mut b = Buffer::with_capacity(10);
        let _ = b.write(&b"abcdefgh"[..]);
        assert_eq!(b.available_data(), 8);
        assert_eq!(b.available_space(), 2);

        assert_eq!(b.replace_slice(&b"ABC"[..], 2, 3), Some(8));
        assert_eq!(b.available_data(), 8);
        assert_eq!(b.available_space(), 2);
        assert_eq!(b.data(), &b"abABCfgh"[..]);

        assert_eq!(b.replace_slice(&b"XYZ"[..], 8, 3), None);
        assert_eq!(b.replace_slice(&b"XYZ"[..], 6, 3), None);

        assert_eq!(b.replace_slice(&b"XYZ"[..], 2, 4), Some(7));
        assert_eq!(b.available_data(), 7);
        assert_eq!(b.available_space(), 3);
        assert_eq!(b.data(), &b"abXYZgh"[..]);

        assert_eq!(b.replace_slice(&b"123"[..], 2, 2), Some(8));
        assert_eq!(b.available_data(), 8);
        assert_eq!(b.available_space(), 2);
        assert_eq!(b.data(), &b"ab123Zgh"[..]);
    }

    use std::str;
    #[test]
    fn set_position() {
        let mut output = [0; 5];
        let mut b = Buffer::with_capacity(10);
        let _ = b.write(&b"abcdefgh"[..]);
        let _ = b.read(&mut output);
        assert_eq!(b.available_data(), 3);
        println!("{:?}", b.position());
    }

    #[test]
    fn consume_without_shift() {
        let mut b = Buffer::with_capacity(10);
        let _ = b.write(&b"abcdefgh"[..]);
        b.consume_noshift(6);
        assert_eq!(b.position(), 6);
    }
}