use crate::emitter::DefaultEmitter;
use crate::offset::{Offset, Position};
use crate::reader::{IntoReader, Reader};
use crate::{Emitter, State, Tokenizer};

/// A naive HTML parser (**not** spec-compliant since it doesn't do tree construction).
///
/// * it **does not** correct [misnested tags]
/// * it **does not** recognize implicitly self-closing elements like
///  `<img>`, it will simply emit a start token
/// * it naively emits any CDATA sections as bogus comments
///
/// It has similar caveats to the [HTMLParser] from the Python standard library.
/// It should suffice for web scraping but you wouldn't use it to implement a browser.
///
/// [misnested tags]: https://html.spec.whatwg.org/multipage/parsing.html#an-introduction-to-error-handling-and-strange-cases-in-the-parser
/// [HTMLParser]: https://docs.python.org/3/library/html.parser.html
pub struct NaiveParser<R: Reader, O: Offset, E: Emitter<O>> {
    tokenizer: Tokenizer<R, O, E>,
}

impl<R: Reader, O: Offset> NaiveParser<R, O, DefaultEmitter<O>> {
    /// Constructs a new naive parser.
    // TODO: add example for NaiveParser::new
    pub fn new<'a>(reader: impl IntoReader<'a, Reader = R>) -> Self {
        let mut tokenizer = Tokenizer::new(reader, DefaultEmitter::default());
        tokenizer.naively_switch_state = true;
        NaiveParser { tokenizer }
    }
}

impl<R: Reader + Position<usize>> NaiveParser<R, usize, DefaultEmitter<usize>> {
    /// Constructs a new naive parser with source code offsets and spans.
    // TODO: add example for NaiveParser::new_with_spans
    pub fn new_with_spans<'a>(reader: impl IntoReader<'a, Reader = R>) -> Self {
        let mut tokenizer = Tokenizer::new(reader, DefaultEmitter::default());
        tokenizer.naively_switch_state = true;
        NaiveParser { tokenizer }
    }
}

impl<R: Reader, O: Offset, E: Emitter<O>> NaiveParser<R, O, E> {
    /// Constructs a new naive parser with a custom emitter.
    // TODO: add example for NaiveParser::new_with_emitter
    pub fn new_with_emitter<'a>(reader: impl IntoReader<'a, Reader = R>, emitter: E) -> Self {
        let mut tokenizer = Tokenizer::new(reader, emitter);
        tokenizer.naively_switch_state = true;
        NaiveParser { tokenizer }
    }
}

impl<R: Reader + Position<O>, O: Offset, E: Emitter<O>> Iterator for NaiveParser<R, O, E> {
    type Item = Result<E::Token, R::Error>;

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

pub(crate) fn naive_next_state(tag_name: &str) -> State {
    // These transitions are defined in https://html.spec.whatwg.org/multipage/parsing.html#parsing-html-fragments.
    // TODO: investigate what state logic Python's HTMLParser is using
    match tag_name {
        "title" | "textarea" => State::RcData,
        "style" | "xmp" | "iframe" | "noembed" | "noframes" => State::RawText,
        "script" => State::ScriptData,
        "plaintext" => State::PlainText,
        _other => State::Data,
    }
}