Presentación de diapositivas automática con botón

Podría crear la presentación de diapositivas automática con un javascript. Pero lo quiero no solo manual, sino también control con botones.

Agregué un código de control manual. Entonces la presentación de diapositivas no funcionaba correctamente. Este es el código para la presentación automática de diapositivas. Cómo modificar esto para trabajar con botones.

var slideIndex = 0;
showSlides();

function showSlides() {
    var i;
    var slides = document.getElementsByClassName("mySlides");
    var dots = document.getElementsByClassName("dot");
    for (i = 0; i < slides.length; i++) {
       slides[i].style.display = "none";  
    }
    slideIndex++;
    if (slideIndex> slides.length) {slideIndex = 1}    
    for (i = 0; i < dots.length; i++) {
        dots[i].className = dots[i].className.replace(" active", "");
    }
    slides[slideIndex-1].style.display = "block";  
    dots[slideIndex-1].className += " active";
    setTimeout(showSlides, 8000); // Change image every 8 seconds
}
#slide{
	width:96%;
	}
	
* {
	box-sizing: border-box
}

.mySlides {
	display: none
}

.slideshow-container {
	width: 1200px;
	position: relative;
	margin: -10px;

}
/* Next & previous buttons */
.prev, .next {
	cursor: pointer;
	position: absolute;
	top: 50%;
	width: auto;
	padding: 16px;
	margin-top: -22px;
	color: white;
	font-weight: bold;
	font-size: 18px;
	transition: 0.6s ease;
	border-radius: 0 3px 3px 0;
}
/* Position the "next button" to the right */
.next {
	right: 0;
	border-radius: 3px 0 0 3px;
}
/* On hover, add a black background color with a little bit see-through */
.prev:hover, .next:hover {
	background-color: rgba(0,0,0,0.8);
}
/* Caption text */
.text {
	color: #f2f2f2;
	font-size: 15px;
	padding: 8px 12px;
	position: absolute;
	bottom: 8px;
	width: 100%;
	text-align: center;
}

/* The dots/bullets/indicators */
.dot {
	cursor: pointer;
	height: 13px;
	width: 13px;
	margin: 0 2px;
	background-color: #bbb;
	border-radius: 50%;
	display: inline-block;
	transition: background-color 0.6s ease;
}
.active, .dot:hover {
	background-color: #717171;
}
/* Fading animation */
.fade {
	-webkit-animation-name: fade;
	-webkit-animation-duration: 2s;
	animation-name: fade;
	animation-duration: 2s;
}
@-webkit-keyframes fade {
  from {opacity: .4} 
  to {opacity: 1}
}

@keyframes fade {
  from {opacity: .4} 
  to {opacity: 1}
}

/* On smaller screens, decrease text size */
@media only screen and (max-width: 300px) {
  .text {font-size: 11px}
}
<div id="slide">
  <div class="slideshow-container">
    <div class="mySlides fade"> <img src="../Images/girl.jpg" style="width:100%"> </div>
    <div class="mySlides fade"> <img src="../Images/bride.jpg" style="width:100%"> </div>
    <div class="mySlides fade"> <img src="../Images/academy.jpg" style="width:100%"> </div>
    <div class="mySlides fade"> <img src="../Images/makeup.jpg" style="width:100%"> </div>
    <a class="prev" onclick="plusSlides(-1)">&#10094;</a> <a class="next" onclick="plusSlides(1)">&#10095;</a> </div>
  <br>
  <div style="text-align:center"> 
  <span class="dot" onclick="currentSlide(1)"></span> 
  <span class="dot" onclick="currentSlide(2)"></span> 
  <span class="dot" onclick="currentSlide(3)"></span>
  <span class="dot" onclick="currentSlide(4)"></span>
   </div>

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