use crate::*;
use self::TokenKind::*;
#[derive(Debug, Copy, Clone, Default, PartialEq)] pub struct Token<'a> {
    source: &'a str,
    start:  usize, 
    length: usize,
    kind:   TokenKind<'a>,
}
#[derive(Debug, Copy, Clone, Default, PartialEq)] pub enum TokenKind<'a> {
    #[default] Nil,
    Err(ParseError),
    Num(usize),
    Sym(&'a str),
    Key(&'a str),
    Exp(usize, TokenIter<'a>),
}
#[derive(Copy, Clone, Debug, PartialEq)] pub struct TokenIter<'a>(pub &'a str);
const_iter!(<'a>|self: TokenIter<'a>| => Token<'a> => self.next_mut().map(|(result, _)|result));
impl<'a> From<&'a str> for TokenIter<'a> {fn from (source: &'a str) -> Self{Self::new(source)}}
impl<'a> TokenIter<'a> {
    pub const fn new (source: &'a str) -> Self { Self(source) }
    pub const fn chomp (&self, index: usize) -> Self { Self(split_at(self.0, index).1) }
    pub const fn next (mut self) -> Option<(Token<'a>, Self)> { Self::next_mut(&mut self) }
    pub const fn peek (&self) -> Option<Token<'a>> { peek_src(self.0) }
    pub const fn next_mut (&mut self) -> Option<(Token<'a>, Self)> {
        match self.peek() {
            Some(token) => Some((token, self.chomp(token.end()))),
            None => None
        }
    }
}
impl<'a> Token<'a> {
    pub const fn new (source: &'a str, kind: TokenKind<'a>, start: usize, length: usize) -> Self {
        Self { source, kind, start, length }
    }
    pub const fn end (&self) -> usize {
        self.start + self.length
    }
    pub const fn slice (&'a self) -> &'a str {
        self.slice_source(self.source)
        //str_range(self.source, self.start, self.end())
    }
    pub const fn slice_source <'b> (&'a self, source: &'b str) -> &'b str {
        str_range(source, self.start, self.end())
    }
    pub const fn kind (&self) -> TokenKind {
        self.kind
    }
    pub const fn error (self, error: ParseError) -> Self {
        Self { kind: TokenKind::Err(error), ..self }
    }
    pub const fn grow (self) -> Self {
        Self { length: self.length + 1, ..self }
    }
    pub const fn grow_in (self) -> Self {
        //Self { length: self.length + 1, depth: self.depth + 1, ..self };
        match self.kind {
            TokenKind::Exp(depth, source) => Self {
                kind: TokenKind::Exp(depth + 1, TokenIter(self.grow().slice_source(source.0))),
                ..self.grow()
            },
            _ => self.grow()
        }
    }
    pub const fn grow_out (self) -> Self {
        match self.kind {
            TokenKind::Exp(depth, source) => match depth {
                0 => self.error(Unexpected(')')),
                d => Self {
                    kind: TokenKind::Exp(d - 1, TokenIter(self.grow().slice_source(source.0))),
                    ..self.grow()
                }
            },
            _ => self.grow()
        }
    }
    //pub const fn to_ref_atom (&self, source: &'a str) -> RefAtom<'a> {
        //match self.kind {
            //TokenKind::Nil => Err(ParseError::Empty),
            //TokenKind::Num => match to_number(self.slice_source(source)) {
                //Err(e) => Err(e),
                //Ok(n) => Ok(RefAtom::Num(n)),
            //},
            //TokenKind::Sym => Ok(RefAtom::Sym(self.slice_source(source))),
            //TokenKind::Key => Ok(RefAtom::Key(self.slice_source(source))),
            //TokenKind::Exp => Ok(
                //RefAtom::Exp(RefAtomIterator(TokenIter::new(self.slice_source(source))))
            //)
        //}
    //}
}
pub const fn peek_src <'a> (source: &'a str) -> Option<Token<'a>> {
    let mut token: Token<'a> = Token::new(source, Nil, 0, 0);
    iterate!(char_indices(source) => (start, c) => token = match token.kind() {
        Err(_) => return Some(token),
        Nil => match c {
            ' '|'\n'|'\r'|'\t' => token.grow(),
            '(' => Token {
                source, start, length: 1,
                kind: TokenKind::Exp(1, TokenIter(str_range(source, start, start + 1))),
            },
            '0'..='9' => Token {
                source, start, length: 1,
                kind: match to_digit(c) {
                    Ok(c) => TokenKind::Num(c),
                    Result::Err(e) => TokenKind::Err(e)
                }
            },
            ':'|'@' => Token {
                source, start, length: 1,
                kind: TokenKind::Sym(str_range(source, start, start + 1)),
            },
            '/'|'a'..='z' => Token {
                source, start, length: 1,
                kind: TokenKind::Key(str_range(source, start, start + 1)),
            },
            _ => token.error(Unexpected(c))
        },
        Num(_) => match c {
            '0'..='9' => token.grow(),
            ' '|'\n'|'\r'|'\t' => return Some(token),
            _ => token.error(Unexpected(c))
        },
        Sym(_) => match c {
            'a'..='z'|'0'..='9'|'-' => token.grow(),
            ' '|'\n'|'\r'|'\t' => return Some(token),
            _ => token.error(Unexpected(c))
        },
        Key(_) => match c {
            'a'..='z'|'0'..='9'|'-'|'/' => token.grow(),
            ' '|'\n'|'\r'|'\t' => return Some(token),
            _ => token.error(Unexpected(c))
        },
        Exp(depth, _) => match depth {
            0 => return Some(token),
            _ => match c {
                ')' => token.grow_out(),
                '(' => token.grow_in(),
                 _  => token.grow(),
            }
        },
    });
    match token.kind() {
        Nil => None,
        _ => Some(token),
    }
}
pub const fn to_number (digits: &str) -> Result<usize, ParseError> {
    let mut value = 0;
    iterate!(char_indices(digits) => (_, c) => match to_digit(c) {
        Ok(digit) => value = 10 * value + digit,
        Result::Err(e) => return Result::Err(e)
    });
    Ok(value)
}
pub const fn to_digit (c: char) -> Result<usize, ParseError> {
    Ok(match c {
        '0' => 0, '1' => 1, '2' => 2, '3' => 3, '4' => 4,
        '5' => 5, '6' => 6, '7' => 7, '8' => 8, '9' => 9,
        _ => return Result::Err(Unexpected(c))
    })
}
#[cfg(test)] #[test] fn test_token () -> Result<(), Box<dyn std::error::Error>> {
    use Token::*;
    assert_eq!(Nil, Token::chomp_one("")?);
    assert_eq!(Nil, Token::chomp_one("  \n    \r   \t  ")?);
    assert_eq!(Num("8", 0, 1), Token::chomp_one("8")?);
    assert_eq!(Num("   8     ", 3, 1), Token::chomp_one("   8     ")?);
    assert_eq!(Sym(":foo", 0, 4), Token::chomp_one(":foo")?);
    assert_eq!(Sym("@bar", 0, 4), Token::chomp_one("@bar")?);
    assert_eq!(Key("foo/bar", 0, 7), Token::chomp_one("foo/bar")?);
    Ok(())
}