use std::collections::btree_map::Entry;
use std::collections::BTreeSet;
use std::collections::VecDeque;
use std::mem;
use std::ops::Range;

use crate::offset::NoopOffset;
use crate::offset::Offset;
use crate::token::{AttrValueSyntax, Comment, Doctype, EndTag, StartTag, Token};
use crate::Emitter;
use crate::Error;

/// The default implementation of [`Emitter`], used to produce tokens.
///
/// # Warning
///
/// * Using the DefaultEmitter without calling [`Tokenizer::set_state`]
///   results in wrong state transitions:
///
///   ```
///   # use html5tokenizer::{DefaultEmitter, Event, Tokenizer, Token};
///   let emitter = DefaultEmitter::default();
///   let html = "<script><b>";
///   let mut tokens = Tokenizer::new(html, emitter).flatten();
///   assert!(matches!(tokens.next().unwrap(), Event::Token(Token::StartTag(tag)) if tag.name == "script"));
///   assert!(matches!(tokens.next().unwrap(), Event::Token(Token::StartTag(tag)) if tag.name == "b"));
///   ```
///
/// [`Tokenizer::set_state`]: crate::Tokenizer::set_state
pub struct DefaultEmitter<O = NoopOffset> {
    current_characters: String,
    current_token: Option<Token<O>>,
    current_attribute: Option<(String, crate::token::AttrInternal<O>)>,
    seen_attributes: BTreeSet<String>,
    emitted_tokens: VecDeque<Token<O>>,
    attr_in_end_tag_span: Option<Range<O>>,
}

impl<O> Default for DefaultEmitter<O> {
    fn default() -> Self {
        DefaultEmitter {
            current_characters: String::new(),
            current_token: None,
            current_attribute: None,
            seen_attributes: BTreeSet::new(),
            emitted_tokens: VecDeque::new(),
            attr_in_end_tag_span: None,
        }
    }
}

impl<O: Offset> Emitter<O> for DefaultEmitter<O> {
    type Token = Token<O>;

    fn emit_eof(&mut self) {
        self.flush_current_characters();
    }

    fn emit_error(&mut self, error: Error, span: Range<O>) {
        self.push_error(error, span);
    }

    fn pop_token(&mut self) -> Option<Self::Token> {
        self.emitted_tokens.pop_back()
    }

    fn emit_string(&mut self, s: &str) {
        self.current_characters.push_str(s);
    }

    fn init_start_tag(&mut self, tag_offset: O, name_offset: O) {
        self.current_token = Some(Token::StartTag(StartTag {
            span: tag_offset..O::default(),
            self_closing: false,
            name: String::new(),
            attributes: Default::default(),
            name_span: name_offset..O::default(),
        }));
    }
    fn init_end_tag(&mut self, tag_offset: O, name_offset: O) {
        self.current_token = Some(Token::EndTag(EndTag {
            span: tag_offset..O::default(),
            name: String::new(),
            name_span: name_offset..O::default(),
        }));
        self.seen_attributes.clear();
    }

    fn init_comment(&mut self, data_start_offset: O) {
        self.current_token = Some(Token::Comment(Comment {
            data: String::new(),
            data_span: data_start_offset..O::default(),
        }));
    }
    fn emit_current_tag(&mut self, offset: O) {
        self.flush_current_attribute();
        let mut token = self.current_token.take().unwrap();
        match &mut token {
            Token::EndTag(tag) => {
                if !self.seen_attributes.is_empty() {
                    let span = self.attr_in_end_tag_span.take().unwrap();
                    self.push_error(Error::EndTagWithAttributes, span);
                }
                self.seen_attributes.clear();
                tag.span.end = offset;
            }
            Token::StartTag(tag) => {
                tag.span.end = offset;
            }
            _ => debug_assert!(false),
        }
        self.emit_token(token);
    }
    fn emit_current_comment(&mut self, data_end_offset: O) {
        let mut token = self.current_token.take().unwrap();
        if let Token::Comment(comment) = &mut token {
            comment.data_span.end = data_end_offset;
        } else {
            debug_assert!(false);
        }
        self.emit_token(token);
    }

    fn emit_current_doctype(&mut self, offset: O) {
        let Some(Token::Doctype(mut doctype)) = self.current_token.take() else {
            debug_assert!(false);
            return;
        };
        doctype.span.end = offset;
        self.emit_token(Token::Doctype(doctype));
    }

    fn set_self_closing(&mut self, slash_span: Range<O>) {
        let tag = self.current_token.as_mut().unwrap();
        match tag {
            Token::StartTag(StartTag {
                ref mut self_closing,
                ..
            }) => {
                *self_closing = true;
            }
            Token::EndTag(_) => {
                self.emit_error(Error::EndTagWithTrailingSolidus, slash_span);
            }
            _ => {
                debug_assert!(false);
            }
        }
    }
    fn set_force_quirks(&mut self) {
        match self.current_token {
            Some(Token::Doctype(ref mut doctype)) => doctype.force_quirks = true,
            _ => debug_assert!(false),
        }
    }
    fn push_tag_name(&mut self, s: &str) {
        match self.current_token {
            Some(Token::StartTag(StartTag { ref mut name, .. })) => {
                name.push_str(s);
            }
            Some(Token::EndTag(EndTag { ref mut name, .. })) => {
                name.push_str(s);
            }
            _ => debug_assert!(false),
        }
    }

    fn terminate_tag_name(&mut self, offset: O) {
        match self.current_token {
            Some(Token::StartTag(StartTag {
                ref mut name_span, ..
            })) => {
                name_span.end = offset;
            }
            Some(Token::EndTag(EndTag {
                ref mut name_span, ..
            })) => {
                name_span.end = offset;
            }
            _ => debug_assert!(false),
        }
    }

    fn push_comment(&mut self, s: &str) {
        match self.current_token {
            Some(Token::Comment(Comment { ref mut data, .. })) => data.push_str(s),
            _ => debug_assert!(false),
        }
    }

    fn init_doctype_name(&mut self, offset: O) {
        let Some(Token::Doctype(doctype)) = &mut self.current_token else {
            debug_assert!(false);
            return;
        };
        doctype.name = Some("".into());
        doctype.name_span.start = offset;
    }

    fn push_doctype_name(&mut self, s: &str) {
        match self.current_token {
            Some(Token::Doctype(Doctype {
                name: Some(ref mut name),
                ..
            })) => name.push_str(s),
            _ => debug_assert!(false),
        }
    }

    fn terminate_doctype_name(&mut self, offset: O) {
        let Some(Token::Doctype(doctype)) = &mut self.current_token else {
            debug_assert!(false);
            return;
        };
        doctype.name_span.end = offset;
    }

    fn init_doctype(&mut self, offset: O) {
        self.current_token = Some(Token::Doctype(Doctype {
            name: None,
            force_quirks: false,
            public_id: None,
            system_id: None,
            span: offset..O::default(),
            name_span: O::default()..O::default(),
            public_id_span: O::default()..O::default(),
            system_id_span: O::default()..O::default(),
        }));
    }

    fn init_attribute_name(&mut self, offset: O) {
        self.flush_current_attribute();
        self.current_attribute = Some((
            String::new(),
            crate::token::AttrInternal {
                name_span: offset..O::default(),
                value: String::new(),
                value_span: O::default()..O::default(),
                value_syntax: None,
            },
        ));
    }
    fn init_attribute_value(&mut self, syntax: AttrValueSyntax, offset: O) {
        let (_, current_attribute) = self.current_attribute.as_mut().unwrap();
        current_attribute.value_span.start = offset;
        current_attribute.value_syntax = Some(syntax);
    }

    fn push_attribute_name(&mut self, s: &str) {
        let current_attr = self.current_attribute.as_mut().unwrap();
        current_attr.0.push_str(s);
    }

    fn terminate_attribute_name(&mut self, offset: O) {
        let current_attr = self.current_attribute.as_mut().unwrap();
        current_attr.1.name_span.end = offset;
    }

    fn push_attribute_value(&mut self, s: &str) {
        let current_attr = self.current_attribute.as_mut().unwrap();
        current_attr.1.value.push_str(s);
    }

    fn terminate_attribute_value(&mut self, offset: O) {
        let current_attr = self.current_attribute.as_mut().unwrap();
        current_attr.1.value_span.end = offset;
    }

    fn init_doctype_public_id(&mut self, offset: O) {
        let Some(Token::Doctype(doctype)) = &mut self.current_token else {
            debug_assert!(false);
            return;
        };
        doctype.public_id = Some("".to_owned());
        doctype.public_id_span.start = offset;
    }
    fn init_doctype_system_id(&mut self, offset: O) {
        let Some(Token::Doctype(doctype)) = &mut self.current_token else {
            debug_assert!(false);
            return;
        };
        doctype.system_id = Some("".to_owned());
        doctype.system_id_span.start = offset;
    }
    fn push_doctype_public_id(&mut self, s: &str) {
        if let Some(Token::Doctype(Doctype {
            public_id: Some(ref mut id),
            ..
        })) = self.current_token
        {
            id.push_str(s);
        } else {
            debug_assert!(false);
        }
    }

    fn terminate_doctype_public_id(&mut self, offset: O) {
        if let Some(Token::Doctype(Doctype {
            ref mut public_id_span,
            ..
        })) = self.current_token
        {
            public_id_span.end = offset;
        } else {
            debug_assert!(false);
        }
    }

    fn push_doctype_system_id(&mut self, s: &str) {
        if let Some(Token::Doctype(Doctype {
            system_id: Some(ref mut id),
            ..
        })) = self.current_token
        {
            id.push_str(s);
        } else {
            debug_assert!(false);
        }
    }

    fn terminate_doctype_system_id(&mut self, offset: O) {
        if let Some(Token::Doctype(Doctype {
            ref mut system_id_span,
            ..
        })) = self.current_token
        {
            system_id_span.end = offset;
        } else {
            debug_assert!(false);
        }
    }
}

impl<O> DefaultEmitter<O> {
    fn emit_token(&mut self, token: Token<O>) {
        self.flush_current_characters();
        self.emitted_tokens.push_front(token);
    }

    fn flush_current_attribute(&mut self)
    where
        O: Offset,
    {
        if let Some((name, map_val)) = self.current_attribute.take() {
            match self.current_token {
                Some(Token::StartTag(ref mut tag)) => match tag.attributes.inner.entry(name) {
                    Entry::Vacant(vacant) => {
                        vacant.insert(map_val);
                    }
                    Entry::Occupied(_) => {
                        self.push_error(Error::DuplicateAttribute, map_val.name_span);
                    }
                },
                Some(Token::EndTag(_)) => {
                    self.attr_in_end_tag_span = Some(map_val.name_span.clone());
                    if !self.seen_attributes.insert(name) {
                        self.push_error(Error::DuplicateAttribute, map_val.name_span);
                    }
                }
                _ => {
                    debug_assert!(false);
                }
            }
        }
    }

    fn flush_current_characters(&mut self) {
        if self.current_characters.is_empty() {
            return;
        }

        let s = mem::take(&mut self.current_characters);
        self.emit_token(Token::String(s));
    }

    fn push_error(&mut self, error: Error, span: Range<O>) {
        // bypass character flushing in self.emit_token: we don't need the error location to be
        // that exact
        self.emitted_tokens.push_front(Token::Error { error, span });
    }
}

/// The majority of our testing of the [`DefaultEmitter`] is done against the
/// html5lib-tests in the html5lib integration test. This module only tests
/// details that aren't present in the html5lib test data.
#[cfg(test)]
mod tests {
    use super::DefaultEmitter;
    use crate::token::{AttrValueSyntax, Token};
    use crate::{Event, Tokenizer};

    #[test]
    fn test_attribute_value_syntax() {
        let mut tokenizer = Tokenizer::new(
            "<div empty unquoted=foo single-quoted='foo' double-quoted=\"foo\">",
            DefaultEmitter::default(),
        )
        .flatten();
        let Event::Token(Token::StartTag(start_tag)) = tokenizer.next().unwrap() else {
            panic!("expected start tag");
        };
        assert_eq!(
            start_tag.attributes.get("empty").unwrap().value_syntax(),
            None
        );
        assert_eq!(
            start_tag.attributes.get("unquoted").unwrap().value_syntax(),
            Some(AttrValueSyntax::Unquoted)
        );
        assert_eq!(
            start_tag
                .attributes
                .get("single-quoted")
                .unwrap()
                .value_syntax(),
            Some(AttrValueSyntax::SingleQuoted)
        );
        assert_eq!(
            start_tag
                .attributes
                .get("double-quoted")
                .unwrap()
                .value_syntax(),
            Some(AttrValueSyntax::DoubleQuoted)
        );
    }
}