compile.rs

use crate::Token;
use crate::TokenType;
use TokenType::*;
use crate::vm::VmError;
use crate::Op::*;
use Precedence::*;
use std::vec::IntoIter;

//only needs lifetime parameter because
//token contains string slice
struct Parser<'a> {
    previous: Token<'a>,
    current: Token<'a>,
}

struct ParseRule {
    prefix: Fn<&mut self>,
    infix: Fn<&mut self>,
    prec: Precedence,
}

#[repr(u8)]
enum Precedence {
    Primary,
    Call,       // . ()
    Unary,      // !
    Factor,     // * /
    Term,       // + -
    Comparison, // > < >= <=
    Equality,
    And,
    Or,
    Assignemnt,
    Null,
}

pub struct Compiler<'a> {
    parser: Parser<'a>,
    tokens: IntoIter<Token<'a>>,
    bytecode: Vec<u8>,
    const_pool: Vec<f64>,
}

impl<'a> Compiler<'a> {

    pub fn new(tokens: Vec<Token<'a>>) -> Self {
        Self {
            tokens: tokens.into_iter(),
            parser: Parser {
                previous: Token {
                    kind: Blank,
                    line_num: 0,
                    content: ""
                },

                current: Token {
                    kind: Blank,
                    line_num: 0,
                    content: ""
                }
            },
            const_pool: vec![],
            bytecode: vec![],
        }
    }

    //just implement the authors way, and change later
    pub fn compile(&mut self) -> Result<Vec<u8>, VmError> {

        while let Some(token) = self.tokens.next() {
            self.parser.previous = self.parser.current;
            self.parser.current = token;

            match token.kind {
                Number => {
                    self.number();
                },

                LeftParen => {
                    //expression() is probably just compile()
                    self.grouping();
                },

                _ => todo!()
            };
        }

        //FIND way to clone without copying when you're not tired
        Ok(std::mem::take(&mut self.bytecode))
    }

    fn expression(&mut self) {
        parse_precedence(Assignemnt);
    }


    //prolly gonna have to change this later
    fn grouping(&mut self) {
        //Never be afraid to express yourself :)
        self.expression();
        if self.tokens.next().map(|token| token.kind) != Some(RightParen) { panic!("Expected ')'"); }
    }

    fn number(&mut self) {
        let val = self.parser.current.content.parse::<f64>().unwrap();
        self.const_pool.push(val);
        if self.const_pool.len() > 256 { panic!("No room in const pool"); }

        self.bytecode.push(OpConstant as u8);
        self.bytecode.push((self.const_pool.len()-1) as u8);
    }

    //keep for now, possibly remove later
    fn unary(&mut self) {
        let op = self.parser.previous.kind;
        self.expression();

        match op {
            Minus => {
                self.bytecode.push(OpNegate as u8);
            },
            _ => unreachable!(),
        };
    }

    //What the fuck
    fn parse_precedence(&mut self, level: Precedence) {

    }

    fn get_rule(&mut self, token_type: TokenType) -> ParseRule {
        let null_fn = || {};

        match token_type {
            LeftParen => ParseRule{ self.grouping, null_fn, Null },
            Minus =>     ParseRule{ self.unary, self.binary, Term },
            Plus =>      ParseRule{ null_fn, self.binary, Term },
            Slash =>     ParseRule{ null_fn, self.binary, Factor },
            Star =>      ParseRule{ null_fn, self.binary, Factor },
            Number =>    ParseRule{ self.number, null_fn, Null },
            _ =>         ParseRule{ null_fn, null_fn, Null },
        }
    }

}



/*
Lox book C code reference:

bool compile(const char* source, Chunk* chunk) {
    initScanner(source);
    advance();
    expression();
    consume(TOKEN_EOF, "Expect end of expression.");
}

//is this handled automatically in loop?
void initScanner(const char* source) {
    scanner.start = source;
    scanner.current = source;
    scanner.line = 1;
}


static void advance() {
    parser.previous = parser.current;
    parser.current = scanToken();
}


//scanner is for scanning TEXT, not tokens
//handle with for loop
Token scanToken() {
    scanner.start = scanner.current;

    if (isAtEnd()) return makeToken(TOKEN_EOF);

    return errorToken("Unexpected character.");
}

static void consume(TokenType type, const char* message) {
    if (parser.current.type == type) {
        advance();
        return;
    }

    errorAtCurrent(message);
}

static void number() {
    double value = strtod(parser.previous.start, NULL);
    emitConstant(value);
}

static void unary() {
    TokenType operatorType = parser.previous.type;

    // Compile the operand.
     expression();

     // Emit the operator instruction.
    switch (operatorType) {
        case TOKEN_MINUS: emitByte(OP_NEGATE); break;
        default: return; // Unreachable.
    }
}

static void parsePrecedence(Precedence precedence) {
  // What goes here?
}
*/