/**
 * @param {string} str
 * @return {number}
 */

const numeric = /^[0-9]+$/;

var myAtoi = function(str) {
  let value = 0;
  let number = "";
  
  if (str === null || str === ""){
    return value;
  }
  
  let validNumber = true;
  let positive = true;
  let startParsing = false;
  
  for (let i = 0; i < str.length; ++i){
    
    let isSpace = /\s/.test(str.charAt(i));
    let isNegative = (str.charAt(i) === '-');
    let isPositive = (str.charAt(i) === '+');
    let isNumeric = (numeric.test(str.charAt(i)));
    
    let validChar = (isSpace || isNegative || isPositive || isNumeric);
    
    if (validChar){
      if (isNegative){
        if (startParsing){
          break;
        }
        positive = false;
        startParsing = true;
      }
      
      if (isPositive){
        if (startParsing){
          break;
        }
        positive = true;
        startParsing = true;
      }
      
      if (isSpace){
        if (startParsing){
          break;
        }
      }
      
      if (isNumeric){
        number += str.charAt(i);
        startParsing = true;
      }
    } else {
      if (!startParsing){
        validNumber = false;
      }
      break;
    }
  }
  
  if (validNumber){
    
    if (number.length === 0){
      return 0;
    }
  
    let output = parseInt(number, 10);
    
    if (output >= 2147483648){
      if (positive){
        output = 2147483647;
      } else {
       output = 2147483648; 
      }
    }
    
    if (!positive){
      output *= -1;
    }

    return output;
  } else {
    return 0;
  }
};