use tokio::io::{AsyncWrite, AsyncBufRead};
use quick_xml::events::{Event, BytesEnd, BytesStart, BytesText};
use quick_xml::name::{Namespace, QName, PrefixDeclaration, ResolveResult, ResolveResult::*};
use quick_xml::reader::NsReader;

use super::error::ParsingError;

// Async traits
pub trait IWrite = AsyncWrite + Unpin;
pub trait IRead = AsyncBufRead + Unpin + 'static;

// Serialization/Deserialization traits
pub trait QWrite {
    async fn qwrite(&self, xml: &mut Writer<impl IWrite>) -> Result<(), quick_xml::Error>; 
}
pub trait QRead<T> {
    async fn qread(&self, xml: &mut Reader<impl IRead>) -> Result<Option<T>, ParsingError>;
}

/// Transform a Rust object into an XML stream of characters
pub struct Writer<T: IWrite> {
    pub q: quick_xml::writer::Writer<T>,
    pub ns_to_apply: Vec<(String, String)>,
}
impl<T: IWrite> Writer<T> {
    pub fn create_dav_element(&mut self, name: &str) -> BytesStart<'static> {
        self.create_ns_element("D", name)
    }
    pub fn create_cal_element(&mut self, name: &str) -> BytesStart<'static> {
        self.create_ns_element("C", name)
    }

    fn create_ns_element(&mut self, ns: &str, name: &str) -> BytesStart<'static> {
        let mut start = BytesStart::new(format!("{}:{}", ns, name));
        if !self.ns_to_apply.is_empty() {
            start.extend_attributes(self.ns_to_apply.iter().map(|(k, n)| (k.as_str(), n.as_str())));
            self.ns_to_apply.clear()
        }
        start
    }
}

/// Transform an XML stream of characters into a Rust object
pub struct Reader<T: IRead> {
    evt: Event<'static>,
    rdr: NsReader<T>,
    buf: Vec<u8>,
}
impl<T: IRead> Reader<T> {
    async fn new(mut rdr: NsReader<T>) -> Result<Self, ParsingError> {
        let mut buf: Vec<u8> = vec![];
        let evt = rdr.read_event_into_async(&mut buf).await?.into_owned();
        buf.clear();
        Ok(Self { evt, rdr, buf })
    }

    fn peek(&self) -> &Event<'static> {
        &self.evt
    }

    /// skip tag. Can't skip end, can't skip eof.
    async fn skip(&mut self) -> Result<Event<'static>, ParsingError> {
        match &self.evt {
            Event::Start(b) => {
                let _span = self.rdr.read_to_end_into_async(b.to_end().name(), &mut self.buf).await?;
                self.next().await
            },
            Event::End(_) => Err(ParsingError::WrongToken),
            Event::Eof => Err(ParsingError::Eof),
            _ => self.next().await,
        }
    }

    /// read one more tag
    async fn next(&mut self) -> Result<Event<'static>, ParsingError> {
       let evt = self.rdr.read_event_into_async(&mut self.buf).await?.into_owned(); 
       self.buf.clear();
       let old_evt = std::mem::replace(&mut self.evt, evt);
       Ok(old_evt)
    }


    /// check if this is the desired tag
    fn is_tag(&self, ns: &[u8], key: &str) -> bool {
        let qname = match self.peek() {
            Event::Start(bs) | Event::Empty(bs) => bs.name(),
            Event::End(be) => be.name(),
            _ => return false,
        };
    
        let (extr_ns, local) = self.rdr.resolve_element(qname);

        if local.into_inner() != key.as_bytes() {
            return false
        }
        
        match extr_ns {
            ResolveResult::Bound(v) => v.into_inner() == ns,
            _ => false,
        }
    }

    /// find start tag
    async fn tag_start(&mut self, ns: &[u8], key: &str) -> Result<Event<'static>, ParsingError> {
        loop {
            match self.peek() {
                Event::Start(b) if self.is_tag(ns, key) => break,
                _ => { self.skip().await?; },
            }
        }
        self.next().await
    }

    // find stop tag
    async fn tag_stop(&mut self, ns: &[u8], key: &str) -> Result<Event<'static>, ParsingError> {
        loop {
            match self.peek() {
                Event::End(b) if self.is_tag(ns, key) => break,
                _ => { self.skip().await?; },
            }
        }
        self.next().await
    }
}