//! This is an implementation of [`Reader`] for reading from a [`AsyncBufRead`]
//! as underlying byte stream. This reader fully implements async/await so reading
//! can use non-blocking I/O.

use std::future::Future;
use std::pin::Pin;
use tokio::io::{self, AsyncBufRead, AsyncBufReadExt};

use crate::events::Event;
use crate::name::{QName, ResolveResult};
use crate::reader::buffered_reader::impl_buffered_source;
use crate::reader::{
    is_whitespace, BangType, NsReader, ParseState, ReadElementState, Reader, Span,
};
use crate::{Error, Result};

/// A struct for read XML asynchronously from an [`AsyncBufRead`].
///
/// Having own struct allows us to implement anything without risk of name conflicts
/// and does not suffer from the impossibility of having `async` in traits.
struct TokioAdapter<'a, R>(&'a mut R);

impl<'a, R: AsyncBufRead + Unpin> TokioAdapter<'a, R> {
    impl_buffered_source!('b, 0, async, await);
}

////////////////////////////////////////////////////////////////////////////////////////////////////

impl<R: AsyncBufRead + Unpin> Reader<R> {
    /// An asynchronous version of [`read_event_into()`]. Reads the next event into
    /// given buffer.
    ///
    /// > This function should be defined as
    /// > ```ignore
    /// > pub async fn read_event_into_async<'b>(
    /// >     &mut self,
    /// >     buf: &'b mut Vec<u8>
    /// > ) -> Result<Event<'b>>;
    /// > ```
    /// > but Rust does not allow to write that for recursive asynchronous function
    ///
    /// This is the main entry point for reading XML `Event`s when using an async reader.
    ///
    /// See the documentation of [`read_event_into()`] for more information.
    ///
    /// # Examples
    ///
    /// ```
    /// # tokio_test::block_on(async {
    /// # use pretty_assertions::assert_eq;
    /// use quick_xml::events::Event;
    /// use quick_xml::reader::Reader;
    ///
    /// // This explicitly uses `from_reader("...".as_bytes())` to use a buffered
    /// // reader instead of relying on the zero-copy optimizations for reading
    /// // from byte slices, which is provides the sync interface anyway.
    /// let mut reader = Reader::from_reader(r#"
    ///     <tag1 att1 = "test">
    ///        <tag2><!--Test comment-->Test</tag2>
    ///        <tag2>Test 2</tag2>
    ///     </tag1>
    /// "#.as_bytes());
    /// reader.trim_text(true);
    ///
    /// let mut count = 0;
    /// let mut buf = Vec::new();
    /// let mut txt = Vec::new();
    /// loop {
    ///     match reader.read_event_into_async(&mut buf).await {
    ///         Ok(Event::Start(_)) => count += 1,
    ///         Ok(Event::Text(e)) => txt.push(e.unescape().unwrap().into_owned()),
    ///         Err(e) => panic!("Error at position {}: {:?}", reader.buffer_position(), e),
    ///         Ok(Event::Eof) => break,
    ///         _ => (),
    ///     }
    ///     buf.clear();
    /// }
    /// assert_eq!(count, 3);
    /// assert_eq!(txt, vec!["Test".to_string(), "Test 2".to_string()]);
    /// # }) // tokio_test::block_on
    /// ```
    ///
    /// [`read_event_into()`]: Reader::read_event_into
    pub fn read_event_into_async<'reader, 'b: 'reader>(
        &'reader mut self,
        buf: &'b mut Vec<u8>,
    ) -> Pin<Box<dyn Future<Output = Result<Event<'b>>> + 'reader>> {
        Box::pin(async move {
            read_event_impl!(
                self, buf,
                TokioAdapter(&mut self.reader),
                read_until_open_async,
                read_until_close_async,
                await
            )
        })
    }

    /// An asynchronous version of [`read_to_end_into()`].
    /// Reads asynchronously until end element is found using provided buffer as
    /// intermediate storage for events content. This function is supposed to be
    /// called after you already read a [`Start`] event.
    ///
    /// See the documentation of [`read_to_end_into()`] for more information.
    ///
    /// # Examples
    ///
    /// This example shows, how you can skip XML content after you read the
    /// start event.
    ///
    /// ```
    /// # tokio_test::block_on(async {
    /// # use pretty_assertions::assert_eq;
    /// use quick_xml::events::{BytesStart, Event};
    /// use quick_xml::reader::Reader;
    ///
    /// let mut reader = Reader::from_reader(r#"
    ///     <outer>
    ///         <inner>
    ///             <inner></inner>
    ///             <inner/>
    ///             <outer></outer>
    ///             <outer/>
    ///         </inner>
    ///     </outer>
    /// "#.as_bytes());
    /// reader.trim_text(true);
    /// let mut buf = Vec::new();
    ///
    /// let start = BytesStart::new("outer");
    /// let end   = start.to_end().into_owned();
    ///
    /// // First, we read a start event...
    /// assert_eq!(reader.read_event_into_async(&mut buf).await.unwrap(), Event::Start(start));
    ///
    /// // ...then, we could skip all events to the corresponding end event.
    /// // This call will correctly handle nested <outer> elements.
    /// // Note, however, that this method does not handle namespaces.
    /// reader.read_to_end_into_async(end.name(), &mut buf).await.unwrap();
    ///
    /// // At the end we should get an Eof event, because we ate the whole XML
    /// assert_eq!(reader.read_event_into_async(&mut buf).await.unwrap(), Event::Eof);
    /// # }) // tokio_test::block_on
    /// ```
    ///
    /// [`read_to_end_into()`]: Self::read_to_end_into
    /// [`Start`]: Event::Start
    pub async fn read_to_end_into_async<'n>(
        &mut self,
        // We should name that lifetime due to https://github.com/rust-lang/rust/issues/63033`
        end: QName<'n>,
        buf: &mut Vec<u8>,
    ) -> Result<Span> {
        Ok(read_to_end!(self, end, buf, read_event_into_async, { buf.clear(); }, await))
    }

    /// Read until '<' is found, moves reader to an `OpenedTag` state and returns a `Text` event.
    async fn read_until_open_async<'b>(&mut self, buf: &'b mut Vec<u8>) -> Result<Event<'b>> {
        read_until_open!(self, buf, TokioAdapter(&mut self.reader), read_event_into_async, await)
    }

    /// Private function to read until `>` is found. This function expects that
    /// it was called just after encounter a `<` symbol.
    async fn read_until_close_async<'b>(&mut self, buf: &'b mut Vec<u8>) -> Result<Event<'b>> {
        read_until_close!(self, buf, TokioAdapter(&mut self.reader), await)
    }
}

////////////////////////////////////////////////////////////////////////////////////////////////////

impl<R: AsyncBufRead + Unpin> NsReader<R> {
    /// An asynchronous version of [`read_event_into()`]. Reads the next event into
    /// given buffer.
    ///
    /// This method manages namespaces but doesn't resolve them automatically.
    /// You should call [`resolve_element()`] if you want to get a namespace.
    ///
    /// You also can use [`read_resolved_event_into_async()`] instead if you want
    /// to resolve namespace as soon as you get an event.
    ///
    /// # Examples
    ///
    /// ```
    /// # tokio_test::block_on(async {
    /// # use pretty_assertions::assert_eq;
    /// use quick_xml::events::Event;
    /// use quick_xml::name::{Namespace, ResolveResult::*};
    /// use quick_xml::reader::NsReader;
    ///
    /// let mut reader = NsReader::from_reader(r#"
    ///     <x:tag1 xmlns:x="www.xxxx" xmlns:y="www.yyyy" att1 = "test">
    ///        <y:tag2><!--Test comment-->Test</y:tag2>
    ///        <y:tag2>Test 2</y:tag2>
    ///     </x:tag1>
    /// "#.as_bytes());
    /// reader.trim_text(true);
    ///
    /// let mut count = 0;
    /// let mut buf = Vec::new();
    /// let mut txt = Vec::new();
    /// loop {
    ///     match reader.read_event_into_async(&mut buf).await.unwrap() {
    ///         Event::Start(e) => {
    ///             count += 1;
    ///             let (ns, local) = reader.resolve_element(e.name());
    ///             match local.as_ref() {
    ///                 b"tag1" => assert_eq!(ns, Bound(Namespace(b"www.xxxx"))),
    ///                 b"tag2" => assert_eq!(ns, Bound(Namespace(b"www.yyyy"))),
    ///                 _ => unreachable!(),
    ///             }
    ///         }
    ///         Event::Text(e) => {
    ///             txt.push(e.unescape().unwrap().into_owned())
    ///         }
    ///         Event::Eof => break,
    ///         _ => (),
    ///     }
    ///     buf.clear();
    /// }
    /// assert_eq!(count, 3);
    /// assert_eq!(txt, vec!["Test".to_string(), "Test 2".to_string()]);
    /// # }) // tokio_test::block_on
    /// ```
    ///
    /// [`read_event_into()`]: NsReader::read_event_into
    /// [`resolve_element()`]: Self::resolve_element
    /// [`read_resolved_event_into_async()`]: Self::read_resolved_event_into_async
    pub async fn read_event_into_async<'b>(&mut self, buf: &'b mut Vec<u8>) -> Result<Event<'b>> {
        self.pop();
        let event = self.reader.read_event_into_async(buf).await;
        self.process_event(event)
    }

    /// An asynchronous version of [`read_to_end_into()`].
    /// Reads asynchronously until end element is found using provided buffer as
    /// intermediate storage for events content. This function is supposed to be
    /// called after you already read a [`Start`] event.
    ///
    /// See the documentation of [`read_to_end_into()`] for more information.
    ///
    /// # Examples
    ///
    /// This example shows, how you can skip XML content after you read the
    /// start event.
    ///
    /// ```
    /// # tokio_test::block_on(async {
    /// # use pretty_assertions::assert_eq;
    /// use quick_xml::name::{Namespace, ResolveResult};
    /// use quick_xml::events::{BytesStart, Event};
    /// use quick_xml::reader::NsReader;
    ///
    /// let mut reader = NsReader::from_reader(r#"
    ///     <outer xmlns="namespace 1">
    ///         <inner xmlns="namespace 2">
    ///             <outer></outer>
    ///         </inner>
    ///         <inner>
    ///             <inner></inner>
    ///             <inner/>
    ///             <outer></outer>
    ///             <p:outer xmlns:p="ns"></p:outer>
    ///             <outer/>
    ///         </inner>
    ///     </outer>
    /// "#.as_bytes());
    /// reader.trim_text(true);
    /// let mut buf = Vec::new();
    ///
    /// let ns = Namespace(b"namespace 1");
    /// let start = BytesStart::from_content(r#"outer xmlns="namespace 1""#, 5);
    /// let end   = start.to_end().into_owned();
    ///
    /// // First, we read a start event...
    /// assert_eq!(
    ///     reader.read_resolved_event_into_async(&mut buf).await.unwrap(),
    ///     (ResolveResult::Bound(ns), Event::Start(start))
    /// );
    ///
    /// // ...then, we could skip all events to the corresponding end event.
    /// // This call will correctly handle nested <outer> elements.
    /// // Note, however, that this method does not handle namespaces.
    /// reader.read_to_end_into_async(end.name(), &mut buf).await.unwrap();
    ///
    /// // At the end we should get an Eof event, because we ate the whole XML
    /// assert_eq!(
    ///     reader.read_resolved_event_into_async(&mut buf).await.unwrap(),
    ///     (ResolveResult::Unbound, Event::Eof)
    /// );
    /// # }) // tokio_test::block_on
    /// ```
    ///
    /// [`read_to_end_into()`]: Self::read_to_end_into
    /// [`Start`]: Event::Start
    pub async fn read_to_end_into_async<'n>(
        &mut self,
        // We should name that lifetime due to https://github.com/rust-lang/rust/issues/63033`
        end: QName<'n>,
        buf: &mut Vec<u8>,
    ) -> Result<Span> {
        // According to the https://www.w3.org/TR/xml11/#dt-etag, end name should
        // match literally the start name. See `Reader::check_end_names` documentation
        self.reader.read_to_end_into_async(end, buf).await
    }

    /// An asynchronous version of [`read_resolved_event_into()`]. Reads the next
    /// event into given buffer asynchronously and resolves its namespace (if applicable).
    ///
    /// Namespace is resolved only for [`Start`], [`Empty`] and [`End`] events.
    /// For all other events the concept of namespace is not defined, so
    /// a [`ResolveResult::Unbound`] is returned.
    ///
    /// If you are not interested in namespaces, you can use [`read_event_into_async()`]
    /// which will not automatically resolve namespaces for you.
    ///
    /// # Examples
    ///
    /// ```
    /// # tokio_test::block_on(async {
    /// # use pretty_assertions::assert_eq;
    /// use quick_xml::events::Event;
    /// use quick_xml::name::{Namespace, QName, ResolveResult::*};
    /// use quick_xml::reader::NsReader;
    ///
    /// let mut reader = NsReader::from_reader(r#"
    ///     <x:tag1 xmlns:x="www.xxxx" xmlns:y="www.yyyy" att1 = "test">
    ///        <y:tag2><!--Test comment-->Test</y:tag2>
    ///        <y:tag2>Test 2</y:tag2>
    ///     </x:tag1>
    /// "#.as_bytes());
    /// reader.trim_text(true);
    ///
    /// let mut count = 0;
    /// let mut buf = Vec::new();
    /// let mut txt = Vec::new();
    /// loop {
    ///     match reader.read_resolved_event_into_async(&mut buf).await.unwrap() {
    ///         (Bound(Namespace(b"www.xxxx")), Event::Start(e)) => {
    ///             count += 1;
    ///             assert_eq!(e.local_name(), QName(b"tag1").into());
    ///         }
    ///         (Bound(Namespace(b"www.yyyy")), Event::Start(e)) => {
    ///             count += 1;
    ///             assert_eq!(e.local_name(), QName(b"tag2").into());
    ///         }
    ///         (_, Event::Start(_)) => unreachable!(),
    ///
    ///         (_, Event::Text(e)) => {
    ///             txt.push(e.unescape().unwrap().into_owned())
    ///         }
    ///         (_, Event::Eof) => break,
    ///         _ => (),
    ///     }
    ///     buf.clear();
    /// }
    /// assert_eq!(count, 3);
    /// assert_eq!(txt, vec!["Test".to_string(), "Test 2".to_string()]);
    /// # }) // tokio_test::block_on
    /// ```
    ///
    /// [`read_resolved_event_into()`]: NsReader::read_resolved_event_into
    /// [`Start`]: Event::Start
    /// [`Empty`]: Event::Empty
    /// [`End`]: Event::End
    /// [`read_event_into_async()`]: Self::read_event_into_async
    pub async fn read_resolved_event_into_async<'ns, 'b>(
        // Name 'ns lifetime, because otherwise we get an error
        // "implicit elided lifetime not allowed here" on ResolveResult
        &'ns mut self,
        buf: &'b mut Vec<u8>,
    ) -> Result<(ResolveResult<'ns>, Event<'b>)> {
        let event = self.read_event_into_async(buf).await;
        self.resolve_event(event)
    }
}

#[cfg(test)]
mod test {
    use super::TokioAdapter;
    use crate::reader::test::{check, small_buffers};

    check!(
        #[tokio::test]
        read_event_into_async,
        read_until_close_async,
        TokioAdapter,
        &mut Vec::new(),
        async, await
    );

    small_buffers!(
        #[tokio::test]
        read_event_into_async: tokio::io::BufReader<_>,
        async, await
    );
}