/** Throws if you pass anything other than a string of length >= 1 
 * @param   String of alphabets. Case insensitive "aBc" === "abc"
 * @returns Boolean true/false
 */


function alphabetSubsequence(str) {
  if (typeof str !== "string" || !str.length) {
    throw new Error("Invalid input");
  }
  const lowerCaseStr = str.toLowerCase();
  const lastIndex = str.length - 1;
  
  for (let i = 0; i < lastIndex; i++) {
    const thisCharCode = lowerCaseStr.charCodeAt(i);
    const nextCharCode = lowerCaseStr.charCodeAt(i + 1);
    if (nextCharCode <= thisCharCode) {
      return false;
    }
    if (thisCharCode < 97 || 122 < thisCharCode) {
      return false;
    }
  }

  const lastCharCode = lowerCaseStr[lastIndex];
  return !(lastCharCode < 97 || lastCharCode > 122);
}




/**
* Test Suite 
*/
describe('alphabetSubsequence()', () => {
    it('returns false when it has duplicate letters', () => {
        // arrange
        const str = 'effg';
        
        // act
        const result = alphabetSubsequence(str);

        // log
        console.log("result 1: ", result);
        
        // assert
        expect(result).toBe(false);
    });

    it('returns false when NOT in ascending a - z order', () => {
        // arrange
        const str = 'cdce';
        
        // act
        const result = alphabetSubsequence(str);

        // log
        console.log("result 2: ", result);
        
        // assert
        expect(result).toBe(false);
    });
    
    it('returns true whenno duplicates and is ascending a - z order ', () => {
        // arrange
        const str = 'ace';
        
        // act
        const result = alphabetSubsequence(str);

        // log
        console.log("result 3: ", result);
        
        // assert
        expect(result).toBe(true);
    });
});