const OP = require('./op.js');


function TokenStream(input){
  var pos = 0;

  function peek(){
    return (pos < input.length) ? input[pos] : null;
  }

  function next(){
    if (pos < input.length){
      let v = input[pos];
      pos += 1;
      return v;
    }
    return null;
  }

  function line(){
    return (pos < input.length) ? input[pos].line : -1;
  }

  function col(){
    return (pos < input.length) ? input[pos].col : -1;
  }

  function eol(){
    return (pos < input.length - 1) ? (input[pos].line !== input[pos+1].line) : true;
  }

  function eof(){
    return (pos >= input.length);
  }

  function die(msg){
    throw new Error(msg + " Line: " + input[pos].line + ", Col: " + input[pos].col);
  }

  return {
    peek: peek,
    next: next,
    line: line,
    col: col,
    eof, eof,
    die: die
  };
}
var stream = null;

function isTokenType(type, val){
  let t = stream.peek();
  if (t !== null && t.type === type){
    if (!val || t.val === val)
      return true;
  }
  return false;
}

function isPunc(ch){
  return isTokenType("punc", ch);
}

function isOpCode(ch){
  return isTokenType("opcode", ch);
}

function isLabel(ch){
  return isTokenType("label", ch);
}

function isDirective(ch){
  return isTokenType("directive", ch);
}

function isOp(ch){
  return isTokenType("op", ch);
}


function skipPunc(ch){
  if (isPunc(ch)){
    stream.next();
  } else {
    stream.die("Unexpected punctuation '" + ch + "'.");
  }
}


parseDelimited(s,e,d,parser){
  let toEOL = (s === null || e === null);
  let a = [];
  let first = true;
  if (!toEOL){skipPunc(s);}
  while (!stream.eof() && ((!toEOL && isPunc(e)) || (toEOL && !stream.eol()))){
    if (first){
      first = false;
    } else {skipPunk(d);}
    a.push(parser());
  }
  if (!toEOL){skipPunc(e);}
  return a;
}


parseOpCode(){
  let val = stream.next();
  let mode = 0; // Guess between absolute and zero page.
  let args = []; // TODO: Finish figuring out how to get the argument list!
  if (isOp("#")){
    stream.next();
    mode = 1; // Immediate
  } else if (isPunc("(")){
    mode = 2; // Indirect
    // TODO: Use parseDelimited()
  }
  return {
    type: "opcode",
    val: val,
    args: args,
    mode: mode
  };
}

parseAtom(){
  if (isPunc("(")){
    stream.next();
    let exp = parseExpression();
    if (isPunc(")")){
      stream.next();
      return exp;
    }
  } else if (isOpCode()){
    return parseOpCode();
  }
}


parse(tokens){
  let p = {
    type: "prog",
    expressions: [];
  };
  stream = TokenStream(tokens);
  while (!stream.eof()){
    p.expressions.push(parseExpression());
  }
  stream = null;
  return p;
}


module.exports = Object.freeze({
  parse: parse
});