#include "lexer.h"
#include <cstdlib>
#include <cstring>
#include <cctype>

/*
 * Return the next lexical element in the string s.
 *  Passing NULL into s, will cause the lexer to read the next element out
 *  of the last string passed in.
 */
LexicalElement
nextElement(char *s) {
  static char *ptr = 0x00;
  LexicalElement result;
  
  //handle pointer reset
  if(s)
    ptr=s;

  //check for the end of the string
  if(!ptr || !*ptr) {
    goto EOS_REACHED;
  }

  //skip white space
  while(*ptr && isspace(*ptr)) ptr++;

  //check for the null terminator
  if(!*ptr) {
    goto EOS_REACHED;
  }

  //handle parens
  if(*ptr == '(') {
    result.type=LPAREN;
    result.value.c = '(';
    ptr++;
  } else if(*ptr == ')') {
    result.type=RPAREN;
    result.value.c = ')';
    ptr++;
  } else if(strchr("*+-/", *ptr)) {
    result.type = OPERATOR;
    result.value.c=*ptr;
    ptr++;
  } else if(isdigit(*ptr) || *ptr=='.') {
    //extract number
    char *end, *begin;
    char *buf;

    //find the end
    begin=ptr;
    ptr++;
    while(isdigit(*ptr) || *ptr=='.') ptr++;
    buf = strndup(begin, end-begin);

    //set up the result
    result.type  = NUMBER;
    result.value.num = atof(buf);

    //get rid of the duped string
    free(buf);
  }  else {
    result.type = ERROR;
    ptr++;
  }

  return result;
  
  //screw Dijkstra, praise Knuth!
  EOS_REACHED:
  result.type=EOS;
  return result;
}