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

use crate::let_else::{assume, know};
use crate::token::{Doctype, EndTag, StartTag, Token};
use crate::trace::AttributeTrace;
use crate::trace::AttributeTraceList;
use crate::trace::{
    AttrValueSyntax, CommentTrace, DoctypeTrace, EndTagTrace, StartTagTrace, Trace,
};
use crate::Emitter;
use crate::Error;

/// The default implementation of [`Emitter`], used to produce tokens.
pub struct TracingEmitter {
    current_token: Option<Token>,
    current_trace: Option<Trace>,
    current_attribute_name: String,
    current_attr_internal: crate::token::AttrInternal,
    current_attribute_trace: crate::trace::AttributeTrace,
    seen_attributes: BTreeSet<String>,
    emitted_tokens: VecDeque<(Token, Trace)>,
    errors: VecDeque<(Error, Range<usize>)>,
    attr_in_end_tag_span: Option<Range<usize>>,
}

impl Default for TracingEmitter {
    fn default() -> Self {
        TracingEmitter {
            current_token: None,
            current_trace: None,
            current_attribute_name: String::new(),
            current_attr_internal: Default::default(),
            current_attribute_trace: crate::trace::AttributeTrace::new(),
            seen_attributes: BTreeSet::new(),
            emitted_tokens: VecDeque::new(),
            errors: VecDeque::new(),
            attr_in_end_tag_span: None,
        }
    }
}

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

impl Iterator for TracingEmitter {
    type Item = (Token, Trace);

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

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

    fn emit_char(&mut self, c: char, span: Range<usize>) {
        self.emit_token(Token::Char(c), Trace::Char(span));
    }

    fn emit_eof(&mut self, offset: usize) {
        self.emit_token(Token::EndOfFile, Trace::EndOfFile(offset));
    }

    fn init_start_tag(&mut self, tag_offset: usize, name_offset: usize) {
        self.current_token = Some(Token::StartTag(StartTag {
            self_closing: false,
            name: String::new(),
            attributes: Default::default(),
        }));
        self.current_trace = Some(Trace::StartTag(StartTagTrace {
            span: tag_offset..0,
            name_span: name_offset..0,
            attribute_traces: AttributeTraceList::new(),
        }));
    }

    fn init_end_tag(&mut self, tag_offset: usize, name_offset: usize) {
        self.current_token = Some(Token::EndTag(EndTag {
            name: String::new(),
        }));
        self.current_trace = Some(Trace::EndTag(EndTagTrace {
            span: tag_offset..0,
            name_span: name_offset..0,
        }));
        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: usize) {
        assume!(
            Some(
                Trace::StartTag(StartTagTrace { name_span, .. })
                    | Trace::EndTag(EndTagTrace { name_span, .. })
            ),
            &mut self.current_trace
        );
        name_span.end = offset;
    }

    fn init_attribute_name(&mut self, offset: usize) {
        self.flush_current_attribute();
        self.current_attribute_trace.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: usize) {
        self.current_attribute_trace.name_span.end = offset;
    }

    fn init_attribute_value(&mut self, syntax: AttrValueSyntax, offset: usize) {
        self.current_attribute_trace.value_span.start = offset;
        self.current_attribute_trace.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: usize) {
        self.current_attribute_trace.value_span.end = offset;
    }

    fn set_self_closing(&mut self, slash_span: Range<usize>) {
        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: usize) {
        self.flush_current_attribute();
        let mut token = self.current_token.take().unwrap();
        let mut trace = self.current_trace.take().unwrap();
        match &mut token {
            Token::EndTag(_) => {
                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();
                know!(Trace::EndTag(tag_trace), &mut trace);
                tag_trace.span.end = offset;
            }
            Token::StartTag(_) => {
                know!(Trace::StartTag(tag_trace), &mut trace);
                tag_trace.span.end = offset;
            }
            other => {
                debug_assert!(false, "unexpected current_token: {other:?}");
                return;
            }
        }
        self.emit_token(token, trace);
    }

    fn init_comment(&mut self, data_start_offset: usize) {
        self.current_token = Some(Token::Comment(String::new()));
        self.current_trace = Some(Trace::Comment(CommentTrace {
            data_span: data_start_offset..0,
        }));
    }

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

    fn emit_current_comment(&mut self, data_end_offset: usize) {
        let token = self.current_token.take().unwrap();
        let mut trace = self.current_trace.take().unwrap();
        assume!(Trace::Comment(comment_trace), &mut trace);
        comment_trace.data_span.end = data_end_offset;
        self.emit_token(token, trace);
    }

    fn init_doctype(&mut self, offset: usize) {
        self.current_token = Some(Token::Doctype(Doctype {
            name: None,
            force_quirks: false,
            public_id: None,
            system_id: None,
        }));
        self.current_trace = Some(Trace::Doctype(DoctypeTrace::new(offset)));
    }

    fn init_doctype_name(&mut self, offset: usize) {
        assume!(Some(Token::Doctype(doctype)), &mut self.current_token);
        doctype.name = Some("".into());
        know!(Some(Trace::Doctype(doctype_trace)), &mut self.current_trace);
        doctype_trace.set_name_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: usize) {
        assume!(Some(Trace::Doctype(doctype_trace)), &mut self.current_trace);
        doctype_trace.set_name_end(offset);
    }

    fn init_doctype_public_id(&mut self, offset: usize) {
        assume!(Some(Token::Doctype(doctype)), &mut self.current_token);
        doctype.public_id = Some("".to_owned());
        know!(Some(Trace::Doctype(doctype_trace)), &mut self.current_trace);
        doctype_trace.set_public_id_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: usize) {
        assume!(Some(Trace::Doctype(doctype_trace)), &mut self.current_trace);
        doctype_trace.set_public_id_end(offset);
    }

    fn init_doctype_system_id(&mut self, offset: usize) {
        assume!(Some(Token::Doctype(doctype)), &mut self.current_token);
        doctype.system_id = Some("".to_owned());
        know!(Some(Trace::Doctype(doctype_trace)), &mut self.current_trace);
        doctype_trace.set_system_id_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: usize) {
        assume!(Some(Trace::Doctype(doctype_trace)), &mut self.current_trace);
        doctype_trace.set_system_id_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: usize) {
        assume!(Some(mut trace), self.current_trace.take());
        assume!(Trace::Doctype(doctype_trace), &mut trace);
        doctype_trace.span.end = offset;
        let token = self.current_token.take().unwrap();
        self.emit_token(token, trace);
    }
}

impl TracingEmitter {
    fn emit_token(&mut self, token: Token, trace: Trace) {
        self.emitted_tokens.push_front((token, trace));
    }

    fn flush_current_attribute(&mut self) {
        if self.current_attribute_name.is_empty() {
            return;
        }
        let name = std::mem::take(&mut self.current_attribute_name);
        let mut attr_internal = std::mem::take(&mut self.current_attr_internal);
        let attr_trace =
            std::mem::replace(&mut self.current_attribute_trace, AttributeTrace::new());

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

impl From<(Token, Trace)> for Token {
    fn from((token, _): (Token, Trace)) -> Self {
        token
    }
}

/// The majority of our testing of the [`TracingEmitter`] 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::TracingEmitter;
    use crate::offset::PosTrackingReader;
    use crate::trace::{AttrValueSyntax, Trace};
    use crate::{Event, Token, Tokenizer};

    #[test]
    fn test_attribute_value_syntax() {
        let mut tokenizer = Tokenizer::new(
            PosTrackingReader::new(
                "<div empty unquoted=foo single-quoted='foo' double-quoted=\"foo\">",
            ),
            TracingEmitter::default(),
        )
        .flatten();
        let Event::Token((Token::StartTag(tag), Trace::StartTag(tag_trace))) =
            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)),
        ] {
            let (_, Some(attr_trace_idx)) = tag.attributes.value_and_trace_idx(name).unwrap()
            else {
                panic!()
            };
            assert_eq!(
                tag_trace.attribute_traces[attr_trace_idx].value_syntax(),
                syntax,
                "unexpected value for attribute {name}"
            );
        }
    }
}