//! convert text into a token stream

use std::io;
use std::fmt;
use super::{identifier, ws0, IResult, Span};
use nom::{
    branch::alt,
    bytes::complete::tag,
    character::complete::{digit1, anychar},
    combinator::{consumed, map, recognize},
    multi::many0,
    error::ParseError,
};

pub struct Token<'a> {
    span: Span<'a>,
    kind: TokenKind,
}

impl fmt::Debug for Token<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{:?} @{} {:?}", self.kind, self.span.location_offset(), self.span.fragment())?;
        Ok(())
    }
}

impl<'a> Token<'a> {
    fn new(span: Span<'a>, kind: TokenKind) -> Self {
        Self { span, kind }
    }
}

pub fn pretty_tokens(mut w: impl io::Write, toks: &[Token]) -> io::Result<()> {
    for tok in toks {
        writeln!(w, "{:?}", tok)?;
    };
    Ok(())
}

#[derive(Debug, PartialEq, Clone)]
pub enum TokenKind {
    // no whitespace, for now
    // no token trees either, for now
    // Braces
    LParen,
    RParen,
    LAngle,
    RAngle,
    LBrace,
    RBrace,
    LSquare,
    RSquare,
    // single chars
    Colon,
    Semicolon,
    Comma,
    Caret,
    Tilde,
    Assign,
    // Multi Chars
    RArrow,
    // Literals
    Ident,
    Number,
    // Keywords
    Module,
    // Error
    Error,
}

#[derive(Debug)]
pub struct TokenSpan<'a> {
    rest: &'a [Token<'a>],
    pos: usize,
}

impl<'a> TokenSpan<'a> {
    pub fn new(rest: &'a [Token<'a>]) -> Self { Self { rest, pos: 0 } }
    pub fn with_pos(rest: &'a [Token<'a>], pos: usize) -> Self { Self { rest, pos } }
}

impl nom::InputTake for TokenSpan<'_> {
    fn take(&self, count: usize) -> Self {
        TokenSpan::with_pos(&self.rest[..count], self.pos + count)
    }

    fn take_split(&self, count: usize) -> (Self, Self) {
        let (head, tail) = &self.rest.split_at(count);
        (TokenSpan::with_pos(&head, self.pos), TokenSpan::with_pos(&tail, self.pos + count))
    }
}

impl nom_greedyerror::Position for TokenSpan<'_> {
    fn position(&self) -> usize {
        self.pos
    }
}

/// combinator that matches a token kind
pub fn token<'a, E>(kind: TokenKind) -> impl FnMut(TokenSpan<'a>) -> nom::IResult<TokenSpan, &Token, E>
    where E: ParseError<TokenSpan<'a>>
{
    move |input: TokenSpan| {
        let next = &input.rest[0];
        if next.kind == kind.clone() {
            let rest = TokenSpan::new(&input.rest[1..]);
            Ok((rest, next))
        }
        else {
            Err(nom::Err::Error(E::from_error_kind(input, nom::error::ErrorKind::Tag)))
        }
    }
}

pub fn lex(input: Span) -> IResult<Span, Vec<Token>> {
    many0(ws0(alt((
        map(tag("module"), |span| Token::new(span, TokenKind::Module)),
        lex_literals,
        lex_braces,
        lex_punctuation,
        map(recognize(anychar), |span| Token::new(span, TokenKind::Error)),
    ))))(input)
}

fn lex_braces(input: Span) -> IResult<Span, Token> {
    map(
        consumed(alt((
            map(tag("("), |_| TokenKind::LParen),
            map(tag(")"), |_| TokenKind::RParen),
            map(tag("<"), |_| TokenKind::LAngle),
            map(tag(">"), |_| TokenKind::RAngle),
            map(tag("{"), |_| TokenKind::LBrace),
            map(tag("}"), |_| TokenKind::RBrace),
            map(tag("["), |_| TokenKind::LSquare),
            map(tag("]"), |_| TokenKind::RSquare),
        ))),
        |(span, kind)| Token::new(span, kind),
    )(input)
}

fn lex_literals(input: Span) -> IResult<Span, Token> {
    map(
        consumed(alt((
            map(identifier, |_| TokenKind::Ident),
            map(digit1, |_| TokenKind::Number),
        ))),
        |(span, kind)| Token::new(span, kind),
    )(input)
}

fn lex_punctuation(input: Span) -> IResult<Span, Token> {
    map(
        consumed(alt((
            map(tag(":"), |_| TokenKind::Colon),
            map(tag(";"), |_| TokenKind::Semicolon),
            map(tag(","), |_| TokenKind::Comma),
            map(tag("^"), |_| TokenKind::Caret),
            map(tag("->"), |_| TokenKind::RArrow),
            map(tag("~"), |_| TokenKind::Tilde),
            map(tag("="), |_| TokenKind::Assign),
        ))),
        |(span, kind)| Token::new(span, kind),
    )(input)
}