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

use crate::let_else::assume;
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.
pub struct DefaultEmitter<O = NoopOffset> {
    current_token: Option<Token<O>>,
    current_attribute_name: String,
    current_attr_internal: crate::token::AttrInternal<O>,
    seen_attributes: BTreeSet<String>,
    emitted_tokens: VecDeque<Token<O>>,
    errors: VecDeque<(Error, Range<O>)>,
    attr_in_end_tag_span: Option<Range<O>>,
}

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

impl<O> DefaultEmitter<O> {
    /// Removes all encountered tokenizer errors and returns them as an iterator.
    pub fn drain_errors(&mut self) -> impl Iterator<Item = (Error, Range<O>)> + '_ {
        self.errors.drain(0..)
    }
}

impl<O> Iterator for DefaultEmitter<O> {
    type Item = Token<O>;

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

impl<O: Offset> Emitter<O> for DefaultEmitter<O> {
    fn report_error(&mut self, error: Error, span: Range<O>) {
        self.errors.push_back((error, span));
    }

    fn emit_char(&mut self, c: char) {
        self.emit_token(Token::Char(c));
    }

    fn emit_eof(&mut self) {
        self.emit_token(Token::EndOfFile);
    }

    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 push_tag_name(&mut self, s: &str) {
        assume!(
            Some(Token::StartTag(StartTag { name, .. }) | Token::EndTag(EndTag { name, .. })),
            &mut self.current_token
        );
        name.push_str(s);
    }

    fn terminate_tag_name(&mut self, offset: O) {
        assume!(
            Some(
                Token::StartTag(StartTag { name_span, .. })
                    | Token::EndTag(EndTag { name_span, .. })
            ),
            &mut self.current_token
        );
        name_span.end = offset;
    }

    fn init_attribute_name(&mut self, offset: O) {
        self.flush_current_attribute();
        self.current_attr_internal.name_span.start = offset;
    }

    fn push_attribute_name(&mut self, s: &str) {
        self.current_attribute_name.push_str(s);
    }

    fn terminate_attribute_name(&mut self, offset: O) {
        self.current_attr_internal.name_span.end = offset;
    }

    fn init_attribute_value(&mut self, syntax: AttrValueSyntax, offset: O) {
        self.current_attr_internal.value_span.start = offset;
        self.current_attr_internal.value_syntax = Some(syntax);
    }

    fn push_attribute_value(&mut self, s: &str) {
        self.current_attr_internal.value.push_str(s);
    }

    fn terminate_attribute_value(&mut self, offset: O) {
        self.current_attr_internal.value_span.end = offset;
    }

    fn set_self_closing(&mut self, slash_span: Range<O>) {
        let token = self.current_token.as_mut().unwrap();

        match token {
            Token::StartTag(tag) => {
                tag.self_closing = true;
            }
            Token::EndTag(_) => {
                self.report_error(Error::EndTagWithTrailingSolidus, slash_span);
            }
            other => debug_assert!(false, "unexpected current_token: {other:?}"),
        }
    }

    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.report_error(Error::EndTagWithAttributes, span);
                }
                self.seen_attributes.clear();
                tag.span.end = offset;
            }
            Token::StartTag(tag) => {
                tag.span.end = offset;
            }
            other => {
                debug_assert!(false, "unexpected current_token: {other:?}");
                return;
            }
        }
        self.emit_token(token);
    }

    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 push_comment(&mut self, s: &str) {
        assume!(Some(Token::Comment(comment)), &mut self.current_token);
        comment.data.push_str(s);
    }

    fn emit_current_comment(&mut self, data_end_offset: O) {
        let mut token = self.current_token.take().unwrap();
        assume!(Token::Comment(comment), &mut token);
        comment.data_span.end = data_end_offset;
        self.emit_token(token);
    }

    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_doctype_name(&mut self, offset: O) {
        assume!(Some(Token::Doctype(doctype)), &mut self.current_token);
        doctype.name = Some("".into());
        doctype.name_span.start = offset;
    }

    fn push_doctype_name(&mut self, s: &str) {
        assume!(
            Some(Token::Doctype(Doctype {
                name: Some(name),
                ..
            })),
            &mut self.current_token
        );
        name.push_str(s);
    }

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

    fn init_doctype_public_id(&mut self, offset: O) {
        assume!(Some(Token::Doctype(doctype)), &mut self.current_token);
        doctype.public_id = Some("".to_owned());
        doctype.public_id_span.start = offset;
    }

    fn push_doctype_public_id(&mut self, s: &str) {
        assume!(
            Some(Token::Doctype(Doctype {
                public_id: Some(public_id),
                ..
            })),
            &mut self.current_token
        );
        public_id.push_str(s);
    }

    fn terminate_doctype_public_id(&mut self, offset: O) {
        assume!(Some(Token::Doctype(doctype)), &mut self.current_token);
        doctype.public_id_span.end = offset;
    }

    fn init_doctype_system_id(&mut self, offset: O) {
        assume!(Some(Token::Doctype(doctype)), &mut self.current_token);
        doctype.system_id = Some("".to_owned());
        doctype.system_id_span.start = offset;
    }

    fn push_doctype_system_id(&mut self, s: &str) {
        assume!(
            Some(Token::Doctype(Doctype {
                system_id: Some(id),
                ..
            })),
            &mut self.current_token
        );
        id.push_str(s);
    }

    fn terminate_doctype_system_id(&mut self, offset: O) {
        assume!(Some(Token::Doctype(doctype)), &mut self.current_token);
        doctype.system_id_span.end = offset;
    }

    fn set_force_quirks(&mut self) {
        assume!(Some(Token::Doctype(doctype)), &mut self.current_token);
        doctype.force_quirks = true;
    }

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

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

    fn flush_current_attribute(&mut self)
    where
        O: Offset,
    {
        if self.current_attribute_name.is_empty() {
            return;
        }
        let name = std::mem::take(&mut self.current_attribute_name);
        let attr_internal = std::mem::take(&mut self.current_attr_internal);

        match &mut self.current_token {
            Some(Token::StartTag(tag)) => match tag.attributes.inner.entry(name) {
                Entry::Vacant(vacant) => {
                    vacant.insert(attr_internal);
                }
                Entry::Occupied(_) => {
                    self.report_error(Error::DuplicateAttribute, attr_internal.name_span);
                }
            },
            Some(Token::EndTag(_)) => {
                self.attr_in_end_tag_span = Some(attr_internal.name_span.clone());
                if !self.seen_attributes.insert(name) {
                    self.report_error(Error::DuplicateAttribute, attr_internal.name_span);
                }
            }
            other => debug_assert!(false, "unexpected current_token: {other:?}"),
        }
    }
}

/// 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(tag)) = tokenizer.next().unwrap() else {
            panic!("expected start tag");
        };
        for (name, syntax) in [
            ("empty", None),
            ("unquoted", Some(AttrValueSyntax::Unquoted)),
            ("single-quoted", Some(AttrValueSyntax::SingleQuoted)),
            ("double-quoted", Some(AttrValueSyntax::DoubleQuoted)),
        ] {
            assert_eq!(
                tag.attributes.get(name).unwrap().value_syntax(),
                syntax,
                "unexpected value for attribute {name}"
            );
        }
    }
}