"use strict";

function main(formName) {
	let result = document.getElementById("result");
	let text = document.forms[formName].elements[0].value;
	let letter = document.forms[formName].elements[1].value;
	
	result.textContent = "Результат: " + changeText(text, letter);
}

function changeText(text, letter) { 
    let result = text.split(" ");
	let words = result.filter( elem => matchWord(elem, letter) );
	result.forEach( (elem, index, array) => 
		array[index] = matchWord(elem, letter) ? getWord(words) : elem );
	return result.join(" ");
}

function matchWord(word, letter) {
	return word.charAt(0).toUpperCase() == letter.toUpperCase() 
}

function getWord(words) {
	let index = Math.floor(Math.random() * words.length);
	return words.splice(index, 1);
}