How to use jQuery validation to set the search bar to accept only a specific input?

This code does the job (there is p instead of a)

jQuery(function(){
        jQuery(".search-submit").click(function(){
        jQuery(".error").hide();
        var hasError = false;
        var searchReg = /^[p0-9]+$/;
        var searchVal = jQuery(".search-field").val();
            var searchLen = searchVal.length;
            var num1 = ['1','2','3','4','5','6','7','8','9'];
            var num0 = ['0','1','2','3','4','5','6','7','8','9'];
        if(searchLen < 3) {
            jQuery(".search-field").after('<span class="error">Enter at least 3 characters.</span>');
            hasError = true;
        } else if(searchLen > 7) {
                  jQuery(".search-field").after('<span class="error">Enter no more than 7 characters.</span>');
            hasError = true;
        } else if(num1.indexOf(searchVal.charAt(0)) == -1) {
                  jQuery(".search-field").after('<span class="error">First character has to be a digit between 1 and 9.</span>');
            hasError = true;
            } else if(num0.indexOf(searchVal.charAt(searchLen-1)) == -1) {
                  jQuery(".search-field").after('<span class="error">Last character has to be a digit between 0 and 9.</span>');
            hasError = true;
            } else if(!searchVal.includes('p')) {
                  jQuery(".search-field").after('<span class="error">You have to enter the character "p".</span>');
            hasError = true;
            } else if((searchVal.match(/p/g) || []).length > 1) {
                  jQuery(".search-field").after('<span class="error">Enter only 1 character "p".</span>');
            hasError = true;
            } else if(!searchReg.test(searchVal)) {
            jQuery(".search-field").after('<span class="error">Enter only digits and one "p" character.</span>');
            hasError = true;
        } else if(searchVal.split('p')[0].length > 3 || searchVal.split('p')[1].length > 3) {
                  jQuery(".search-field").after('<span class="error">Exercise and page have to be numbers between 1 and 999.</span>');
            hasError = true;
            } else if(searchVal.charAt(searchVal.indexOf('p')+1) == '0') {
                  jQuery(".search-field").after('<span class="error">Page first digit cannot be 0.</span>');
            hasError = true;
            }
        if(hasError == true) {return false;}
    });
});