//! Contains a parser for an XML element.

use crate::errors::SyntaxError;

use crate::parser::Parser;

/// A parser that search a `>` symbol in the slice outside of quoted regions.

///

/// The parser considers two quoted regions: a double-quoted (`"..."`) and

/// a single-quoted (`'...'`) region. Matches found inside those regions are not

/// considered as results. Each region starts and ends by its quote symbol,

/// which cannot be escaped (but can be encoded as XML character entity or named

/// entity. Anyway, that encoding does not contain literal quotes).

///

/// To use a parser create an instance of parser and [`feed`] data into it.

/// After successful search the parser will return [`Some`] with position of

/// found symbol. If search is unsuccessful, a [`None`] will be returned. You

/// typically would expect positive result of search, so that you should feed

/// new data until you get it.

///

/// NOTE: after successful match the parser does not returned to the initial

/// state and should not be used anymore. Create a new parser if you want to perform

/// new search.

///

/// # Example

///

/// ```

/// # use pretty_assertions::assert_eq;

/// use quick_xml::parser::{ElementParser, Parser};

///

/// let mut parser = ElementParser::default();

///

/// // Parse `<my-element  with = 'some > inside'>and the text follow...`

/// // splitted into three chunks

/// assert_eq!(parser.feed(b"<my-element"), None);

/// // ...get new chunk of data

/// assert_eq!(parser.feed(b" with = 'some >"), None);

/// // ...get another chunk of data

/// assert_eq!(parser.feed(b" inside'>and the text follow..."), Some(8));

/// //                       ^       ^

/// //                       0       8

/// ```

///

/// [`feed`]: Self::feed()

#[derive(Clone, Copy, Debug, Eq, PartialEq)]

pub enum ElementParser {

    /// The initial state (inside element, but outside of attribute value).

    Outside,

    /// Inside a single-quoted region (`'...'`).

    SingleQ,

    /// Inside a double-quoted region (`"..."`).

    DoubleQ,

}

impl Parser for ElementParser {

    /// Returns number of consumed bytes or `None` if `>` was not found in `bytes`.

    #[inline]

    fn feed(&mut self, bytes: &[u8]) -> Option<usize> {

        for i in memchr::memchr3_iter(b'>', b'\'', b'"', bytes) {

            *self = match (*self, bytes[i]) {

                // only allowed to match `>` while we are in state `Outside`

                (Self::Outside, b'>') => return Some(i),

                (Self::Outside, b'\'') => Self::SingleQ,

                (Self::Outside, b'\"') => Self::DoubleQ,

                // the only end_byte that gets us out if the same character

                (Self::SingleQ, b'\'') | (Self::DoubleQ, b'"') => Self::Outside,

                // all other bytes: no state change

                _ => continue,

            };

        }

        None

    }

    #[inline]

    fn eof_error(self, _content: &[u8]) -> SyntaxError {

        match self {

            Self::Outside => SyntaxError::UnclosedTag,

            Self::SingleQ => SyntaxError::UnclosedSingleQuotedAttributeValue,

            Self::DoubleQ => SyntaxError::UnclosedDoubleQuotedAttributeValue,

        }

    }

}

impl Default for ElementParser {

    #[inline]

    fn default() -> Self {

        Self::Outside

    }

}

#[test]

fn parse() {

    use pretty_assertions::assert_eq;

    use ElementParser::*;

    /// Returns `Ok(pos)` with the position in the buffer where element is ended.

    ///

    /// Returns `Err(internal_state)` if parsing does not done yet.

    fn parse_element(bytes: &[u8], mut parser: ElementParser) -> Result<usize, ElementParser> {

        match parser.feed(bytes) {

            Some(i) => Ok(i),

            None => Err(parser),

        }

    }

    assert_eq!(parse_element(b"", Outside), Err(Outside));

    assert_eq!(parse_element(b"", SingleQ), Err(SingleQ));

    assert_eq!(parse_element(b"", DoubleQ), Err(DoubleQ));

    assert_eq!(parse_element(b"'", Outside), Err(SingleQ));

    assert_eq!(parse_element(b"'", SingleQ), Err(Outside));

    assert_eq!(parse_element(b"'", DoubleQ), Err(DoubleQ));

    assert_eq!(parse_element(b"\"", Outside), Err(DoubleQ));

    assert_eq!(parse_element(b"\"", SingleQ), Err(SingleQ));

    assert_eq!(parse_element(b"\"", DoubleQ), Err(Outside));

    assert_eq!(parse_element(b">", Outside), Ok(0));

    assert_eq!(parse_element(b">", SingleQ), Err(SingleQ));

    assert_eq!(parse_element(b">", DoubleQ), Err(DoubleQ));

    assert_eq!(parse_element(b"''>", Outside), Ok(2));

    assert_eq!(parse_element(b"''>", SingleQ), Err(SingleQ));

    assert_eq!(parse_element(b"''>", DoubleQ), Err(DoubleQ));

}