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use std::collections::VecDeque;
use error::StreamError;
use stream::{Positioned, Resetable, StreamErrorFor, StreamOnce};
#[derive(Debug, PartialEq)]
pub struct BufferedStream<I>
where
I: StreamOnce + Positioned,
{
offset: usize,
iter: I,
buffer_offset: usize,
buffer: VecDeque<(I::Item, I::Position)>,
}
impl<I> Resetable for BufferedStream<I>
where
I: Positioned,
{
type Checkpoint = usize;
fn checkpoint(&self) -> Self::Checkpoint {
self.offset
}
fn reset(&mut self, checkpoint: Self::Checkpoint) {
self.offset = checkpoint;
}
}
impl<I> BufferedStream<I>
where
I: StreamOnce + Positioned,
I::Position: Clone,
I::Item: Clone,
{
pub fn new(iter: I, lookahead: usize) -> BufferedStream<I> {
BufferedStream {
offset: 0,
iter: iter,
buffer_offset: 0,
buffer: VecDeque::with_capacity(lookahead),
}
}
}
impl<I> Positioned for BufferedStream<I>
where
I: StreamOnce + Positioned,
{
#[inline(always)]
fn position(&self) -> Self::Position {
if self.offset >= self.buffer_offset {
self.iter.position()
} else if self.offset < self.buffer_offset - self.buffer.len() {
self.buffer
.front()
.expect("At least 1 element in the buffer")
.1
.clone()
} else {
self.buffer[self.buffer.len() - (self.buffer_offset - self.offset)]
.1
.clone()
}
}
}
impl<I> StreamOnce for BufferedStream<I>
where
I: StreamOnce + Positioned,
I::Item: Clone + PartialEq,
{
type Item = I::Item;
type Range = I::Range;
type Position = I::Position;
type Error = I::Error;
#[inline]
fn uncons(&mut self) -> Result<I::Item, StreamErrorFor<Self>> {
if self.offset >= self.buffer_offset {
let position = self.iter.position();
let item = try!(self.iter.uncons());
self.buffer_offset += 1;
if self.buffer.len() == self.buffer.capacity() {
self.buffer.pop_front();
}
self.buffer.push_back((item.clone(), position.clone()));
self.offset += 1;
Ok(item)
} else if self.offset < self.buffer_offset - self.buffer.len() {
Err(StreamError::message_static_message(
"Backtracked to far".into(),
))
} else {
let value = self.buffer[self.buffer.len() - (self.buffer_offset - self.offset)]
.0
.clone();
self.offset += 1;
Ok(value)
}
}
}