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#![cfg_attr(not(feature = "std"), no_std)]

#[cfg(feature = "alloc")]
extern crate alloc;

use core::{
    future::Future,
    pin::Pin,
    task::{Context, Poll},
};

pub mod iter;
#[cfg(feature = "nom-adapters")]
pub mod nom;
pub mod read;
pub mod utf8;

#[derive(Debug, PartialEq, Eq, Hash)]
pub enum Streaming<T> {
    Item(T),
    Incomplete,
}

pub type Parsed<T> = (Option<T>, usize);

pub trait Buffer {
    type Output: ?Sized;

    fn buffer(&mut self) -> (&Self::Output, &mut usize);
    fn exhausted(&self) -> bool;
}

pub trait Advance {
    type Error;

    fn advance(&mut self) -> Result<(), Self::Error>;
}

pub trait AdvanceAsync {
    type Error;

    fn poll_advance(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>>;
}

pub trait Parse<'i> {
    type Input: 'i;
    type Output;
    type Error;

    fn parse(&mut self, input: Self::Input)
        -> Result<Streaming<Parsed<Self::Output>>, Self::Error>;

    fn parse_eof(&mut self, input: Self::Input) -> Result<Parsed<Self::Output>, Self::Error>;
}

#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
struct AdvanceAsyncFuture<'a, B: ?Sized>(&'a mut B);

impl<B> Future for AdvanceAsyncFuture<'_, B>
where
    B: ?Sized + AdvanceAsync + Unpin,
{
    type Output = Result<(), B::Error>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let this = &mut *self;
        Pin::new(&mut *this.0).poll_advance(cx)
    }
}

pub(crate) fn advance_async<B>(src: &mut B) -> impl Future<Output = Result<(), B::Error>> + '_
where
    B: ?Sized + AdvanceAsync + Unpin,
{
    AdvanceAsyncFuture(src)
}

pub struct StreamParser<P, S> {
    parser: P,
    source: S,
}

impl<P, S> StreamParser<P, S> {
    pub fn new(parser: P, source: S) -> Self {
        StreamParser { parser, source }
    }

    pub fn advance(&mut self) -> Result<(), S::Error>
    where
        S: Advance,
    {
        self.source.advance()
    }

    pub fn advance_async(&mut self) -> impl Future<Output = Result<(), S::Error>> + '_
    where
        S: AdvanceAsync + Unpin,
    {
        advance_async(&mut self.source)
    }

    pub fn get(&mut self) -> Result<Option<Streaming<<P as Parse>::Output>>, <P as Parse>::Error>
    where
        S: Buffer,
        for<'i> P: Parse<'i, Input = &'i S::Output>,
    {
        let exhausted = self.source.exhausted();
        let (input, pos) = self.source.buffer();
        match self.parser.parse(input) {
            Ok(Streaming::Item((output, parsed))) => {
                *pos += parsed;
                Ok(output.map(Streaming::Item))
            }
            Ok(Streaming::Incomplete) => {
                if exhausted {
                    match self.parser.parse_eof(input) {
                        Ok((output, parsed)) => {
                            *pos += parsed;
                            Ok(output.map(Streaming::Item))
                        }
                        Err(err) => Err(err),
                    }
                } else {
                    Ok(Some(Streaming::Incomplete))
                }
            }
            Err(err) => Err(err),
        }
    }
}

#[cfg(all(doctest, feature = "std"))]
doc_comment::doctest!("../README.md");

#[cfg(test)]
mod tests;