script.js

class MinHeap {
	constructor() {
		this.heap_array = [];
	}
	size() {
		return this.heap_array.length;
	}
	empty() {
		return (this.size() === 0);
	}
	push(value) {
		this.heap_array.push(value);
		this.up_heapify();
	}
	up_heapify() {
		var current_index = this.size() - 1;
		while (current_index > 0) {
			var current_element = this.heap_array[current_index];
			var parent_index = Math.trunc((current_index - 1) / 2);
			var parent_element = this.heap_array[parent_index];

			if (parent_element[0] < current_element[0]) {
				break;
			}
			else {
				this.heap_array[parent_index] = current_element;
				this.heap_array[current_index] = parent_element;
				current_index = parent_index;
			}
		}
	}
	top() {
		return this.heap_array[0];
	}
	pop() {
		if (this.empty() == false) {
			var last_index = this.size() - 1;
			this.heap_array[0] = this.heap_array[last_index];
			this.heap_array.pop();
			this.down_heapify();
		}
	}
	down_heapify() {
		var current_index = 0;
		var current_element = this.heap_array[0];
		while (current_index < this.size()) {
			var child_index1 = (current_index * 2) + 1;
			var child_index2 = (current_index * 2) + 2;
			if (child_index1 >= this.size() && child_index2 >= this.size()) {
				break;
			}
			else if (child_index2 >= this.size()) {
				let child_element1 = this.heap_array[child_index1];
				if (current_element[0] < child_element1[0]) {
					break;
				}
				else {
					this.heap_array[child_index1] = current_element;
					this.heap_array[current_index] = child_element1;
					current_index = child_index1;
				}
			}
			else {
				var child_element1 = this.heap_array[child_index1];
				var child_element2 = this.heap_array[child_index2];
				if (current_element[0] < child_element1[0] && current_element[0] < child_element2[0]) {
					break;
				}
				else {
					if (child_element1[0] < child_element2[0]) {
						this.heap_array[child_index1] = current_element;
						this.heap_array[current_index] = child_element1;
						current_index = child_index1;
					}
					else {
						this.heap_array[child_index2] = current_element;
						this.heap_array[current_index] = child_element2;
						current_index = child_index2;
					}
				}
			}
		}
	}
}
class Codec {
	getCodes(node, curr_code) {
		if (typeof (node[1]) === "string") {
			this.codes[node[1]] = curr_code;
			return;
		}
		this.getCodes(node[1][0], curr_code + '0');
		this.getCodes(node[1][1], curr_code + '1');
	}
	make_string(node) {
		if (typeof (node[1]) === "string") {
			return "'" + node[1];
		}
		return '0' + this.make_string(node[1][0]) + '1' + this.make_string(node[1][1]);
	}
	make_tree(tree_string) {
		let node = [];
		if (tree_string[this.index] === "'") {
			this.index++;
			node.push(tree_string[this.index]);
			this.index++;
			return node;
		}
		this.index++;
		node.push(this.make_tree(tree_string));
		this.index++;
		node.push(this.make_tree(tree_string));
		return node;
	}
	encode(data) {
		this.heap = new MinHeap();

		var mp = new Map();
		for (let i = 0; i < data.length; i++) {
			if (mp.has(data[i])) {
				let foo = mp.get(data[i]);
				mp.set(data[i], foo + 1);
			}
			else {
				mp.set(data[i], 1);
			}
		}
		if (mp.size === 0) {
			let final_string = "zer#";
			
			let output_message = "Compression complete and file will be downloaded automatically." + '\n' + "Compression Ratio : " + (data.length / final_string.length).toPrecision(6);
			return [final_string, output_message];
		}

		if (mp.size === 1) {
			let key, value;
			for (let [k, v] of mp) {
				key = k;
				value = v;
			}
			let final_string = "one" + '#' + key + '#' + value.toString();
			let output_message = "Compression complete and file will be downloaded automatically." + '\n' + "Compression Ratio : " + (data.length / final_string.length).toPrecision(6);
			return [final_string, output_message];
		}
		for (let [key, value] of mp) {
			this.heap.push([value, key]);
		}
		while (this.heap.size() >= 2) {
			let min_node1 = this.heap.top();
			this.heap.pop();
			let min_node2 = this.heap.top();
			this.heap.pop();
			this.heap.push([min_node1[0] + min_node2[0], [min_node1, min_node2]]);
		}
		var huffman_tree = this.heap.top();
		this.heap.pop();
		this.codes = {};
		this.getCodes(huffman_tree, "");

		/// convert data into coded data
		let binary_string = "";
		for (let i = 0; i < data.length; i++) {
			binary_string += this.codes[data[i]];
		}
		let padding_length = (8 - (binary_string.length % 8)) % 8;
		for (let i = 0; i < padding_length; i++) {
			binary_string += '0';
		}
		let encoded_data = "";
		for (let i = 0; i < binary_string.length;) {
			let curr_num = 0;
			for (let j = 0; j < 8; j++, i++) {
				curr_num *= 2;
				curr_num += binary_string[i] - '0';
			}
			encoded_data += String.fromCharCode(curr_num);
		}
		let tree_string = this.make_string(huffman_tree);
		let ts_length = tree_string.length;
		let final_string = ts_length.toString() + '#' + padding_length.toString() + '#' + tree_string + encoded_data;
		let output_message = "Compression complete and file will be downloaded automatically." + '\n' + "Compression Ratio : " + (data.length / final_string.length).toPrecision(6);
		return [final_string, output_message];
	}

	decode(data) {
		let k = 0;
		let temp = "";
		while (k < data.length && data[k] != '#') {
			temp += data[k];
			k++;
		}
		if (k == data.length){
			alert("Invalid File! Please submit a valid De-Compressed file");
			location.reload();
			return;
		}
		if (temp === "zer") {
			let decoded_data = "";
			let output_message = "De-Compression complete and file will be downloaded automatically.";
			return [decoded_data, output_message];
		}
		if (temp === "one") {
			data = data.slice(k + 1);
			k = 0;
			temp = "";
			while (data[k] != '#') {
				temp += data[k];
				k++;
			}
			let one_char = temp;
			data = data.slice(k + 1);
			let str_len = parseInt(data);
			let decoded_data = "";
			for (let i = 0; i < str_len; i++) {
				decoded_data += one_char;
			}
			let output_message = "De-Compression complete and file will be downloaded automatically.";
			return [decoded_data, output_message];

		}
		data = data.slice(k + 1);
		let ts_length = parseInt(temp);
		k = 0;
		temp = "";
		while (data[k] != '#') {
			temp += data[k];
			k++;
		}
		data = data.slice(k + 1);
		let padding_length = parseInt(temp);
		temp = "";
		for (k = 0; k < ts_length; k++) {
			temp += data[k];
		}
		data = data.slice(k);
		let tree_string = temp;
		temp = "";
		for (k = 0; k < data.length; k++) {
			temp += data[k];
		}
		let encoded_data = temp;
		this.index = 0;
		var huffman_tree = this.make_tree(tree_string);

		let binary_string = "";
		for (let i = 0; i < encoded_data.length; i++) {
			let curr_num = encoded_data.charCodeAt(i);
			let curr_binary = "";
			for (let j = 7; j >= 0; j--) {
				let foo = curr_num >> j;
				curr_binary = curr_binary + (foo & 1);
			}
			binary_string += curr_binary;
		}
		binary_string = binary_string.slice(0, -padding_length);
		let decoded_data = "";
		let node = huffman_tree;
		for (let i = 0; i < binary_string.length; i++) {
			if (binary_string[i] === '1') {
				node = node[1];
			}
			else {
				node = node[0];
			}

			if (typeof (node[0]) === "string") {
				decoded_data += node[0];
				node = huffman_tree;
			}
		}
		let output_message = "De-Compression complete and file will be downloaded automatically.";
		return [decoded_data, output_message];
	}
}

window.onload = function () {
	decodeBtn = document.getElementById("decode");
	encodeBtn = document.getElementById("encode");
	uploadFile = document.getElementById("uploadfile")
	submitBtn = document.getElementById("submitbtn");
	step1 = document.getElementById("step1");
	step2 = document.getElementById("step2");
	step3 = document.getElementById("step3");
	codecObj = new Codec();

	submitBtn.onclick = function () {
		var uploadedFile = uploadFile.files[0];
		if (uploadedFile === undefined) {
			alert("No file uploaded.\nPlease upload a file and try again");
			return;
		}
		let nameSplit = uploadedFile.name.split('.');
		var extension = nameSplit[nameSplit.length - 1].toLowerCase();
		if (extension != "txt") {
			alert("Invalid file type (." + extension + ") \nPlease upload a valid .txt file and try again");
			return;
		}
		document.getElementById("step1").style.display = "none";
		document.getElementById("step2").style.display = "inline-flex";
		document.getElementById("startagain").style.visibility = "visible";
	}

	encodeBtn.onclick = function () {
		var uploadedFile = uploadFile.files[0];
		if (uploadedFile === undefined) {
			alert("No file uploaded.\nPlease upload a file and try again");
			return;
		}
		console.log(uploadedFile.size);
		if(uploadedFile.size === 0){
			alert("You have uploaded an empty file!\nThe compressed file might be larger in size than the uncompressed file (compression ratio might be smaller than one).\nBetter compression ratios are achieved for larger file sizes!");
		}	
		else if(uploadedFile.size <= 350){
			alert("The uploaded file is very small in size (" + uploadedFile.size +" bytes) !\nThe compressed file might be larger in size than the uncompressed file (compression ratio might be smaller than one).\nBetter compression ratios are achieved for larger file sizes!");
		}
		else if(uploadedFile.size < 1000){
			alert("The uploaded file is small in size (" + uploadedFile.size +" bytes) !\nThe compressed file's size might be larger than expected (compression ratio might be small).\nBetter compression ratios are achieved for larger file sizes!");
		}
		onclickChanges2("Compressing your file ...\n", "Compressed");
		var fileReader = new FileReader();
		fileReader.onload = function (fileLoadedEvent) {
			let text = fileLoadedEvent.target.result;
			let [encodedString, outputMsg] = codecObj.encode(text);
			myDownloadFile(uploadedFile.name.split('.')[0] + "_compressed.txt", encodedString);
			ondownloadChanges(outputMsg);
		}
		fileReader.readAsText(uploadedFile, "UTF-8");
		document.getElementById("step2").style.display = "none";
		document.getElementById("step3").style.display = "inline-flex";
	}

	decodeBtn.onclick = function () {
		console.log("decode onclick");
		var uploadedFile = uploadFile.files[0];
		if (uploadedFile === undefined) {
			alert("No file uploaded.\nPlease upload a file and try again!");
			return;
		}
		onclickChanges2("De-compressing your file ...\n", "De-Compressed");
		var fileReader = new FileReader();
		fileReader.onload = function (fileLoadedEvent) {
			let text = fileLoadedEvent.target.result;
			let [decodedString, outputMsg] = codecObj.decode(text);
			myDownloadFile(uploadedFile.name.split('.')[0] + "_decompressed.txt", decodedString);
			ondownloadChanges(outputMsg);
		}
		fileReader.readAsText(uploadedFile, "UTF-8");
		document.getElementById("step2").style.display = "none";
		document.getElementById("step3").style.display = "inline-flex";
	}

}
function botVoice1(message) {
    const speech = new SpeechSynthesisUtterance();
	if (message==="uplaod"){
		speech.text = "Please select an action to compress or decompress the file";
	}
	speech.volume = 1;
    speech.rate = 0.75;
    speech.pitch = 1;
    window.speechSynthesis.speak(speech);
  
}

document.getElementById("submitbtn").addEventListener("click",function(){
  botVoice1("uplaod");
});
function botVoice2(message) {
   const speech = new SpeechSynthesisUtterance();
	if (message==="uplaod"){
		speech.text = "De-Compression complete and file will be downloaded automatically.";
	}
	speech.volume = 1;
    speech.rate = 0.75;
    speech.pitch = 1;
    window.speechSynthesis.speak(speech);
  
}

document.getElementById("decode").addEventListener("click",function(){
  botVoice2("uplaod");
});
function botVoice3(message) {
    const speech = new SpeechSynthesisUtterance();
	if (message==="uplaod"){
		speech.text = "Succesfully compressed the file and file will be downloaded automatically. ";
	}
	speech.volume = 1;
    speech.rate = 0.75;
    speech.pitch = 1;
    window.speechSynthesis.speak(speech);
  
}

document.getElementById("encode").addEventListener("click",function(){
  botVoice3("uplaod");
});
function onclickChanges2(secMsg, word) {
	decodeBtn.disabled = true;
	encodeBtn.disabled = true;
	step3.innerHTML = "";
	let msg2 = document.createElement("span");
	msg2.className = "text2";
	msg2.innerHTML = secMsg;
	step3.appendChild(msg2);
	let msg3 = document.createElement("span");
	msg3.className = "text2";
	msg3.innerHTML = word + " file will be downloaded automatically!";
	step3.appendChild(msg3);
}

function myDownloadFile(fileName, text) {
	let a = document.createElement('a');
	a.href = "data:application/octet-stream," + encodeURIComponent(text);
	a.download = fileName;
	a.click();
}

function ondownloadChanges(outputMsg) {
	step3.innerHTML = "";
	let img = document.createElement("img");
	img.src = "done.jpg";
	img.id = "doneImg";
	step3.appendChild(img);
	var br = document.createElement("br");
	step3.appendChild(br);
	let msg3 = document.createElement("span");
	msg3.className = "text2";
	msg3.innerHTML = outputMsg;
	step3.appendChild(msg3);
}