const PRECEDENCE = {
  "#": 0, // Precedence 0 should be ignored!
  "=": 1,
  "<":7, "<=":7, ">":7, ">=":7, "==":7, "!=":7,
  "+": 10, "-": 10,
  "*": 20, "/": 20
};

function TokenStream(input){
  var pos = 0;

  function peek(off){
    off = off || 0;
    return (pos+off < input.length) ? input[pos+off] : 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 > 0 && pos < input.length) ? (input[pos-1].line !== input[pos].line) : true;
  }

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

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

  function getPos(){return pos;}

  return {
    peek: peek,
    next: next,
    line: line,
    col: col,
    pos: getPos,
    eol: eol,
    eof, eof,
    die: die
  };
}
// var stream = null;
// var SKIPEOL = false;


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




class Parser{
  constructor(pof){
    if (typeof(pof) !== 'function')
      throw new TypeError("Expected op code parsing function.");
    this.__stream = null;
    this.__SKIPEOL = false;
    this.__output = null;
    this.__PCLabel = "__PC__";
    this.parseOpCode = pof(this);
  }

  set tokens(t){
    this.__stream = new TokenStream(t);
    this.__output = null;
    this.__SKIPEOL = false;
  }
  get stream(){return this.__stream;}

  get PCLabel(){return this.__PCLabel;}
  set PCLabel(pcl){
    if (typeof(pcl) !== 'string' || pcl === "")
      throw new TypeError("PC Label must be a non-zero-length string.");
    this.__PCLabel = pcl;
  }
 

  isPunc(ch){
    return isTokenType(this.stream, "punc", ch);
  }

  isOpCode(ch){
    return isTokenType(this.stream, "opcode", ch);
  }

  isLabel(ch){
    return isTokenType(this.stream, "label", ch);
  }

  isDirective(ch){
    return isTokenType(this.stream, "directive", ch);
  }

  isOp(ch){
    return isTokenType(this.stream, "op", ch);
  }


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


  skipDirective(ch){
    if (!this.isDirective(ch))
      this.stream.die("Unexpected directive '" + ch + "'.");
    this.stream.next();
  }


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

  parseByteDirective(){
    let line = this.stream.line();
    let col = this.stream.col();
    this.stream.next();
    return {
      type: "directive",
      op: ".byte",
      args: this.parseDelimited(null, null,
        ",",
        this.parseExpression.bind(this)
      ),
      line: line,
      col: col
    }
  }


  parseElseIfDirective(){
    this.skipDirective(".elif");
    let cond = this.parseExpression();
    this.skipDirective(".then");
    let then = this.parseBlock([".else", ".elif", ".endif"]);
    let f = {
      type: "directive",
      op: "if",
      cond: cond,
      then: then
    }
    if (this.isDirective(".elif")){
      f["else"] = this.parseElseIfDirective();
    } else if (this.isDirective(".else")){
      this.skipDirective(".else");
      f["else"] = this.parseBlock([".endif"]);
    } else if(!this.isDirective(".endif")){
      this.stream.die("Expected '.endif' Directive.");
    }
    return f;
  }


  parseIfDirective(){
    this.skipDirective(".if");
    let cond = this.parseExpression();
    this.skipDirective(".then");
    let then = this.parseBlock([".elif", ".else", ".endif"]);
    let f = {
      type: "directive",
      op: "if",
      cond: cond,
      then: then
    };
    if (this.isDirective(".elif")){
      f["else"] = this.parseElseIfDirective();  
    } else if (this.isDirective(".else")){
      this.skipDirective(".else");
      f["else"] = this.parseBlock([".endif"]);
    }
    this.skipDirective(".endif");
    return f;
  }

  parseLabel(t){
    if (!this.stream.eof()){
      let ct = this.stream.peek();
      if (ct.type === "opcode" && t.col === t.val.length){
        this.__SKIPEOL = true;
        return {
          type: "assign",
          op: "=",
          left: t,
          right: this.__PCLabel, // To designate "current program counter".
          line: t.line,
          col: t.col
        }
      }
    }
    return t;
  }

  parseTempLabel(){
    let isEOL = this.stream.eol();
    this.stream.next();
    if (isEOL){
      this.__SKIPEOL = true;
      return {
        type:"temp-label",
        val:-1, // Value of -1 means "set new temp label"
        line:this.stream.line(),
        col:this.stream.col()
      };
    }
    let t = this.stream.next();
    if (t.type === "number"){
      t.type = "temp-label";
      return t;
    }
    this.stream.die("Temp label missing index. New temp labels must be defined at the start of the line.");
  }

  parseAtom(){
    if (this.isPunc("(")){
      this.stream.next();
      let exp = this.parseExpression();
      if (this.isPunc(")")){
        this.stream.next();
        return exp;
      }
    } else if (this.isPunc(":")){
      return this.parseTempLabel();
    } else if (this.isOpCode()){
      return this.parseOpCode();
    } else if (this.isDirective(".if")){
      return this.parseIfDirective();
    } else if (this.isDirective(".bytes")){
      return this.parseByteDirective();
    }

    let tok = this.stream.next();
    if (tok.type === "number" || tok.type === "string"){ 
      return tok;
    } else if (tok.type === "label"){
      return this.parseLabel(tok);
    }
    this.stream.die("Unexpected token {type:" + tok.type + ", val:'" + tok.val + "'}.");
  }


  parseExpression(){
    return this.maybeCall((function(){
      return this.maybeBinary(this.parseAtom(), 0);
    }).bind(this));
  }

  parseCall(func){
    return {
      type: "call",
      func: func,
      args: this.parseDelimited(
        "(", ")",
        ",",
        this.parseExpression.bind(this)
      )
    };
  }

  maybeCall(expr){
    expr = expr();
    return (this.isOp("(")) ? this.parseCall(expr) : expr;
  }

  maybeBinary(left, pres){
    let tok = this.isOp();
    if (tok){
      let cpres = PRECEDENCE[tok.val];
      if (cpres > pres){
        this.stream.next();
        return this.maybeBinary({
          type: (tok.val === "=") ? "assign" : "binary",
          op: tok.val,
          left: left,
          right: this.maybeBinary(this.parseAtom(), cpres),
          line: tok.line,
          col: tok.col
        }, pres);
      }
    }
    return left;
  }


  parseBlock(bed){
    let line = this.stream.line();
    let col = this.stream.col();
    let exp = [];
    let isBlockEnd = (t) => {
      return (bed && t.type === 'directive' && bed.indexOf(t.val) >= 0);
    }
    while (!this.stream.eof()){
      if (isBlockEnd(this.stream.peek()))
        break;
      exp.push(this.parseExpression());
      if (!this.stream.eol()){
        if (!this.__SKIPEOL)
          this.stream.die("Expected End of Line.");
        this.__SKIPEOL = false;
      }
    }
    return {
      type: "block",
      expressions: exp,
      line: line,
      col: col
    };
  }

  /*
  parseProg(){
    let line = this.stream.line();
    let col = this.stream.col();
    return {
      type: "prog",
      block: this.parseBlock(),
      line: line,
      col: col
    };
  }
  */

  parse(tokens){
    if (tokens)
      this.tokens = tokens;

    if (this.__stream !== null){
      if (this.__output === null && this.__stream.pos() === 0)
        this.__output = this.parseBlock();
      return this.__output;
    }
    return null;
  }
}


module.exports = Parser;