Fixes: #156 - Base64 encode and decode algorithms

DIRECTORY.md

@@ -5,6 +5,9 @@
 ## Backtracking
   * [Open Knight Tour](https://github.com/TheAlgorithms/Dart/blob/master/backtracking/open_knight_tour.dart)
 
+## Ciphers
+  * [Base64 Encoding](https://github.com/TheAlgorithms/Dart/blob/master/ciphers/base64_encoding.dart)
+
 ## Conversions
   * [Binary To Decimal](https://github.com/TheAlgorithms/Dart/blob/master/conversions/binary_to_decimal.dart)
   * [Binary To Hexadecimal](https://github.com/TheAlgorithms/Dart/blob/master/conversions/binary_to_hexadecimal.dart)

ciphers/base64_encoding.dart

@@ -0,0 +1,119 @@
+import 'dart:math';
+import 'dart:typed_data';
+
+import 'package:test/test.dart';
+
+const B64_CHARSET =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+String base64Encode(Uint8List data) {
+  String binaryStream = '';
+  data.forEach((byte) {
+    binaryStream += byte.toRadixString(2).padLeft(8, '0');
+  });
+
+  bool paddingNeeded = binaryStream.length % 6 != 0;
+
+  String padding = '';
+  if (paddingNeeded) {
+    // The padding that will be added later
+    padding = '=' * ((6 - binaryStream.length % 6) / 2).floor();
+    // Append binary_stream with arbitrary binary digits (0's by default) to make its length a multiple of 6
+    binaryStream += '0' * (6 - binaryStream.length % 6);
+  }
+
+  // Encode every 6 binary digits to their corresponding Base64 character
+  String base64EncodedData = '';
+  for (int i = 0; i < binaryStream.length; i = i + 6) {
+    base64EncodedData +=
+        B64_CHARSET[int.parse(binaryStream.substring(i, i + 6), radix: 2)];
+  }
+  return base64EncodedData + padding;
+}
+
+Uint8List base64Decode(String data) {
+  List<String> splittedData = data.split('');
+  int padding = splittedData.where((c) => c == '=').length;
+
+  // Check if the encoded string contains non base64 characters
+  if (splittedData
+      .sublist(0, splittedData.length - padding)
+      .any((c) => !B64_CHARSET.contains(c))) {
+    throw Exception('Invalid base64 character(s) found.');
+  }
+
+  // Check the padding
+  if (data.length % 4 != 0 || padding >= 3) {
+    throw Exception('Incorrect padding.');
+  }
+
+  // Remove padding
+  splittedData = splittedData.sublist(0, splittedData.length - padding);
+
+  String binaryStream = '';
+  splittedData.forEach((c) {
+    binaryStream += B64_CHARSET.indexOf(c).toRadixString(2).padLeft(6, '0');
+  });
+
+  if (padding > 0) {
+    binaryStream = binaryStream.substring(0, binaryStream.length - padding * 2);
+  }
+
+  List<int> base64DecodedData = [];
+  for (int i = 0; i < binaryStream.length; i = i + 8) {
+    int end = min(i + 8, binaryStream.length);
+    base64DecodedData.add(int.parse(binaryStream.substring(i, end), radix: 2));
+  }
+
+  return Uint8List.fromList(base64DecodedData);
+}
+
+void main() {
+  Uint8List convertStringToUint8List(String input) {
+    return Uint8List.fromList(input.codeUnits);
+  }
+
+  test(('base64Encode: Hello World'), () {
+    Uint8List data = convertStringToUint8List('Hello World');
+    expect(base64Encode(data), 'SGVsbG8gV29ybGQ=');
+  });
+
+  test(('base64Decode: SGVsbG8gV29ybGQ= (aka Hello World)'), () {
+    expect(base64Decode('SGVsbG8gV29ybGQ='),
+        convertStringToUint8List('Hello World'));
+  });
+
+  test(('base64Encode and base64Decode'), () {
+    const LOREM_IPSUM = [
+      'lorem',
+      'ipsum',
+      'dolor',
+      'sit',
+      'amet',
+      'consectetur',
+      'adipiscing',
+      'elit',
+      'curabitur',
+      'vel',
+      'hendrerit',
+      'libero',
+      'eleifend',
+      'blandit',
+      'nunc',
+      'ornare',
+      'odio',
+      'ut',
+      'orci',
+      'gravida',
+      'imperdiet',
+      'nullam',
+      'purus',
+      'lacinia',
+    ];
+
+    for (var word in LOREM_IPSUM) {
+      Uint8List sutAsUint8List = convertStringToUint8List(word);
+      expect(base64Decode(base64Encode(sutAsUint8List)), sutAsUint8List);
+    }
+  });
+}