use circular::Buffer;
use futures::Stream;
use nom::Err;
use std::{
    collections::{BTreeMap, HashMap, HashSet},
    path::Prefix,
    str::{self, FromStr},
};
use tokio::io::{AsyncBufRead, AsyncBufReadExt, AsyncRead, AsyncReadExt};

static MAX_STANZA_SIZE: usize = 65536;

use crate::{
    element::{Content, Element, Name, Namespace},
    error::Error,
    xml::{self, parsers::Parser},
    Result,
};

/// streaming reader that tracks depth and available namespaces at current depth
pub struct Reader<R> {
    inner: R,
    buffer: Buffer,
    // holds which tags we are in atm over depth
    // to have names reference namespaces could
    depth: Vec<Name>,
    namespaces: Vec<HashSet<Namespace>>,
}

impl<R> Reader<R> {
    pub fn new(reader: R) -> Self {
        Self {
            inner: reader,
            buffer: Buffer::with_capacity(MAX_STANZA_SIZE),
            depth: Vec::new(),
            namespaces: Vec::new(),
        }
    }
}

impl<R> Reader<R>
where
    R: AsyncRead + Unpin,
{
    async fn read_buf(&mut self) -> Result<usize> {
        Ok(self.inner.read_buf(&mut self.buffer).await?)
    }

    async fn read_element<'s>(&'s mut self) -> Result<Element> {
        self.read_buf().await?;
        let mut input = str::from_utf8(self.buffer.data())?;
        loop {
            match xml::Element::parse(input) {
                Ok((rest, e)) => {
                    let len = self.buffer.available_data() - rest.as_bytes().len();
                    let element = Reader::<R>::element_from_xml(&mut self.namespaces, e)?;
                    self.buffer.consume(len);
                    return Ok(element);
                }
                std::result::Result::Err(e) => match e {
                    Err::Incomplete(_) => {
                        self.read_buf().await?;
                        input = str::from_utf8(self.buffer.data())?;
                    }
                    // TODO: better error
                    Err::Error(e) => return Err(Error::ParseError(e.to_string())),
                    Err::Failure(e) => return Err(Error::ParseError(e.to_string())),
                },
            }
        }
    }
}

impl<R> Reader<R> {
    fn element_from_xml(
        namespaces: &mut Vec<HashSet<Namespace>>,
        element: xml::Element,
    ) -> Result<Element> {
        match element {
            xml::Element::Empty(empty_elem_tag) => {
                let mut namespace_declarations = HashSet::new();
                for (prefix, namespace) in
                    empty_elem_tag.attributes.iter().filter_map(|attribute| {
                        if let xml::Attribute::NamespaceDeclaration { ns_name, value } = attribute {
                            Some((ns_name, value))
                        } else {
                            None
                        }
                    })
                {
                    let prefix = match prefix {
                        xml::NSAttName::PrefixedAttName(prefixed_att_name) => {
                            Some(prefixed_att_name.to_string())
                        }
                        xml::NSAttName::DefaultAttName => None,
                    };
                    let namespace = Namespace {
                        prefix,
                        namespace: namespace.process()?,
                    };
                    if !namespace_declarations.insert(namespace.clone()) {
                        return Err(Error::DuplicateNameSpace(namespace));
                    }
                }

                // all namespaces available to the element (from both parent elements and element itself)
                let namespace_stack: Vec<&Namespace> = namespaces
                    .iter()
                    .flatten()
                    .chain(namespace_declarations.iter())
                    .collect();

                let mut attributes = HashMap::new();

                for (q_name, value) in empty_elem_tag.attributes.iter().filter_map(|attribute| {
                    if let xml::Attribute::Attribute { name, value } = attribute {
                        Some((name, value))
                    } else {
                        None
                    }
                }) {
                    let namespace;
                    let attribute_name;
                    match q_name {
                        xml::QName::PrefixedName(prefixed_name) => {
                            namespace = namespace_stack.iter().rfind(|namespace| {
                                namespace.prefix.as_deref() == Some(**prefixed_name.prefix)
                            });
                            attribute_name = prefixed_name.local_part.to_string();
                        }
                        xml::QName::UnprefixedName(unprefixed_name) => {
                            namespace = namespace_stack
                                .iter()
                                .rfind(|namespace| namespace.prefix == None);
                            attribute_name = unprefixed_name.to_string();
                        }
                    }
                    if let Some(namespace) = namespace {
                        let namespace = (*namespace).clone();
                        let name = Name {
                            namespace,
                            name: attribute_name,
                        };
                        let value = value.process()?;
                        if let Some(_value) = attributes.insert(name, value) {
                            return Err(Error::DuplicateAttribute(q_name.to_string()));
                        }
                    } else {
                        return Err(Error::UnqualifiedNamespace(q_name.to_string()));
                    }
                }

                let name;
                let namespace;
                match &empty_elem_tag.name {
                    xml::QName::PrefixedName(prefixed_name) => {
                        namespace = namespace_stack.iter().rfind(|namespace| {
                            namespace.prefix.as_deref() == Some(**prefixed_name.prefix)
                        });
                        name = prefixed_name.local_part.to_string();
                    }
                    xml::QName::UnprefixedName(unprefixed_name) => {
                        namespace = namespace_stack
                            .iter()
                            .rfind(|namespace| namespace.prefix == None);
                        name = unprefixed_name.to_string();
                    }
                }

                let namespace = (*namespace
                    .ok_or_else(|| Error::UnqualifiedNamespace(empty_elem_tag.name.to_string()))?)
                .clone();

                let name = Name { namespace, name };

                return Ok(Element {
                    name,
                    namespace_decl: namespace_declarations,
                    attributes,
                    content: Vec::new(),
                });
            }
            xml::Element::NotEmpty(s_tag, content, e_tag) => {
                if s_tag.name != e_tag.name {
                    return Err(Error::MismatchedEndTag(
                        s_tag.name.to_string(),
                        e_tag.name.to_string(),
                    ));
                }
                let mut namespace_declarations = HashSet::new();
                for (prefix, namespace) in s_tag.attributes.iter().filter_map(|attribute| {
                    if let xml::Attribute::NamespaceDeclaration { ns_name, value } = attribute {
                        Some((ns_name, value))
                    } else {
                        None
                    }
                }) {
                    let prefix = match prefix {
                        xml::NSAttName::PrefixedAttName(prefixed_att_name) => {
                            Some(prefixed_att_name.to_string())
                        }
                        xml::NSAttName::DefaultAttName => None,
                    };
                    let namespace = Namespace {
                        prefix,
                        namespace: namespace.process()?,
                    };
                    if !namespace_declarations.insert(namespace.clone()) {
                        return Err(Error::DuplicateNameSpace(namespace));
                    }
                }

                // all namespaces available to the element (from both parent elements and element itself)
                let namespace_stack: Vec<&Namespace> = namespaces
                    .iter()
                    .flatten()
                    .chain(namespace_declarations.iter())
                    .collect();

                let mut attributes = HashMap::new();

                for (q_name, value) in s_tag.attributes.iter().filter_map(|attribute| {
                    if let xml::Attribute::Attribute { name, value } = attribute {
                        Some((name, value))
                    } else {
                        None
                    }
                }) {
                    let namespace;
                    let attribute_name;
                    match q_name {
                        xml::QName::PrefixedName(prefixed_name) => {
                            namespace = namespace_stack.iter().rfind(|namespace| {
                                namespace.prefix.as_deref() == Some(**prefixed_name.prefix)
                            });
                            attribute_name = prefixed_name.local_part.to_string();
                        }
                        xml::QName::UnprefixedName(unprefixed_name) => {
                            namespace = namespace_stack
                                .iter()
                                .rfind(|namespace| namespace.prefix == None);
                            attribute_name = unprefixed_name.to_string();
                        }
                    }
                    if let Some(namespace) = namespace {
                        let namespace = (*namespace).clone();
                        let name = Name {
                            namespace,
                            name: attribute_name,
                        };
                        let value = value.process()?;
                        if let Some(_value) = attributes.insert(name, value) {
                            return Err(Error::DuplicateAttribute(q_name.to_string()));
                        }
                    } else {
                        return Err(Error::UnqualifiedNamespace(q_name.to_string()));
                    }
                }

                let name;
                let namespace;
                match &s_tag.name {
                    xml::QName::PrefixedName(prefixed_name) => {
                        namespace = namespace_stack.iter().rfind(|namespace| {
                            namespace.prefix.as_deref() == Some(**prefixed_name.prefix)
                        });
                        name = prefixed_name.local_part.to_string();
                    }
                    xml::QName::UnprefixedName(unprefixed_name) => {
                        namespace = namespace_stack
                            .iter()
                            .rfind(|namespace| namespace.prefix == None);
                        name = unprefixed_name.to_string();
                    }
                }

                let namespace = (*namespace
                    .ok_or_else(|| Error::UnqualifiedNamespace(s_tag.name.to_string()))?)
                .clone();

                let name = Name { namespace, name };

                namespaces.push(namespace_declarations.clone());

                let content = Self::content_from_xml(namespaces, content)?;

                namespaces.pop();

                return Ok(Element {
                    name,
                    namespace_decl: namespace_declarations,
                    attributes,
                    content,
                });
            }
        }
    }

    fn content_from_xml(
        namespaces: &mut Vec<HashSet<Namespace>>,
        element: xml::Content,
    ) -> Result<Vec<Content>> {
        let mut content = Vec::new();
        let mut text = element.char_data.map(|str| String::from(*str));
        for (content_item, char_data) in element.content {
            match content_item {
                xml::ContentItem::Element(element) => {
                    text.map(|text| content.push(Content::Text(text)));
                    content.push(Content::Element(Self::element_from_xml(
                        namespaces, element,
                    )?));
                    text = char_data.map(|str| String::from(*str));
                }
                xml::ContentItem::Reference(reference) => {
                    let data = reference.process()?;
                    if let Some(text) = &mut text {
                        text.push(data)
                    } else {
                        text = Some(String::from(data))
                    }
                    char_data.map(|char_data| text.as_mut().map(|s| s.push_str(*char_data)));
                }
                xml::ContentItem::CDSect(cd_sect) => {
                    if let Some(text) = &mut text {
                        text.push_str(**cd_sect)
                    } else {
                        text = Some(String::from(**cd_sect))
                    }
                    char_data.map(|char_data| text.as_mut().map(|s| s.push_str(*char_data)));
                }
                // TODO: is this important?
                xml::ContentItem::PI(pi) => {
                    char_data.map(|char_data| text.as_mut().map(|s| s.push_str(*char_data)));
                }
                // TODO: comments?
                xml::ContentItem::Comment(comment) => {
                    char_data.map(|char_data| text.as_mut().map(|s| s.push_str(*char_data)));
                }
            }
        }
        text.map(|text| content.push(Content::Text(text)));
        todo!()
    }
}

// impl<R> Reader<R>
// where
//     R: AsyncBufReadExt + Unpin,
// {
//     /// could resursively read and include namespace tree with values to be shadowed within new local context
//     async fn read_recursive(&mut self, namespaces: BTreeMap<Option<String>, String>) -> Result<Element, Error> {
//         let element;
//         let len;
//         loop {
//             let buf = self.inner.fill_buf().await?;
//             let input = str::from_utf8(buf)?;
//             match crate::xml::element(input) {
//                 Ok((rest, e)) => {
//                     element = e;
//                     len = buf.len() - rest.len();
//                     break;
//                 }
//                 Err(e) => match e {
//                     Err::Incomplete(_) => (),
//                     e => return Err::<E, Error>(Error::ParseError(input.to_owned())),
//                 },
//             }
//         }

//         let final;
//         match element {
//             crate::xml::Element::Empty(e) => {
//                 let final = Element {

//                 }
//             },
//             crate::xml::Element::NotEmpty(_, _, _) => todo!(),
//         }

//         self.inner.consume(len);
//         todo!()
//     }
// /// reads entire next prolog, element, or misc
// pub async fn read<E: From<Element>>(&mut self) -> Result<E, Error> {
//     let element;
//     let len;
//     loop {
//         let buf = self.inner.fill_buf().await?;
//         let input = str::from_utf8(buf)?;
//         match crate::xml::element(input) {
//             Ok((rest, e)) => {
//                 element = e;
//                 len = buf.len() - rest.len();
//                 break;
//             }
//             Err(e) => match e {
//                 Err::Incomplete(_) => (),
//                 e => return Err::<E, Error>(Error::ParseError(input.to_owned())),
//             },
//         }
//     }
//     self.inner.consume(len);

//     // Ok(element)
//     todo!()
// }
// pub async fn read_start(&self) -> Result<impl From<Element>, Error> {
//     todo!()
// }
// pub async fn read_end(&self) -> Result<(), Error> {
//     todo!()
// }
// }

// impl<R: AsyncBufRead> Stream for Reader<R> {
//     type Item = impl From<Element>;

//     async fn poll_next(
//         self: std::pin::Pin<&mut Self>,
//         cx: &mut std::task::Context<'_>,
//     ) -> std::task::Poll<Option<Self::Item>> {
//         todo!()
//     }
// }