Dart : How to check if password contains all required characters

dart.password.check

# Dart: Validate Password

This code snippet shows how to validate a password 
**Requirement** : 
Password should be more than 8 characters long 
It should contain 
at least one Uppercase ( Capital ) letter 
at least one lowercase character 
at least digit and 
special character. 


    void main() {
     	 var p = "ComplextPassword@123";
     	 //will print True if password is complient else false
    	 print(isPasswordCompliant(p));
    }
    
    // Password validation function
    bool isPasswordCompliant(String password)
      {
      	
        bool isComplient = false;
        bool hasUppercase  = false;
        bool hasDigits = false;
        bool hasLowercase = false;
        bool hasSpecialCharacters = false;
        var character='';
        var i=0;
      	print(password);
        if (! password?.isEmpty) {
          	// Check if valid special characters are present
         		hasSpecialCharacters = password.contains(new RegExp(r'[!@#$%^&*(),.?":{}|<>]'));  
            while (i < password.length){
               character = password.substring(i,i+1);
               print(character);
               
               if (isDigit(character , 0)){
                  hasDigits=true;
              }else{
                 	
                  if (character == character.toUpperCase()) {
                      hasUppercase=true;
                  }
                  if (character == character.toLowerCase()){
                      hasLowercase=true;
                  }
              }
              i++;
            }
        }
      	isComplient = hasDigits & hasUppercase & hasLowercase & hasSpecialCharacters;
        return isComplient;
      }
    
      bool isDigit(String s, int idx) =>
        "0".compareTo(s[idx]) <= 0 && "9".compareTo(s[idx]) >= 0;