[4sem] isaip01 done

4sem/isaip/01/PlayfairCypher/Models/PlayfairCrypto.cs

@@ -0,0 +1,161 @@
+// ReSharper disable StringLiteralTypo
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace PlayfairCypher.Models {
+    public class PlayfairCrypto {
+        private static readonly HashSet<char> EnAlphabet = new("ABCDEFGHIKLMNOPQRSTUVWXYZ");
+    
+        public string Encrypt(string keyword, string text) {
+            var keyTable = GenerateTable(keyword);
+            var pairs = FormPairs(text);
+
+            var data = new StringBuilder(32);
+            
+            foreach (var pair in pairs) {
+                var idx1 = FindCharIndex(ref keyTable, pair[0]);
+                var idx2 = FindCharIndex(ref keyTable, pair[1]);
+
+                var x1 = idx1 / 5;  // x for rows
+                var y1 = idx1 % 5;  // and y for cols
+                var x2 = idx2 / 5;
+                var y2 = idx2 % 5;
+
+                char c1, c2;
+                if (y1 == y2) {
+                    c1 = keyTable[WrapIndex(x1 + 1), y1];
+                    c2 = keyTable[WrapIndex(x2 + 1), y1];
+                }
+                else if (x1 == x2) {
+                    c1 = keyTable[x1, WrapIndex(y1 + 1)];
+                    c2 = keyTable[x1, WrapIndex(y2 + 1)];
+                }
+                else {
+                    c1 = keyTable[x1, y2];
+                    c2 = keyTable[x2, y1];
+                }
+                
+                data.Append(c1).Append(c2);
+            }
+
+            return data.ToString();
+        }
+    
+        public string Decrypt(string keyword, string text) {
+            var keyTable = GenerateTable(keyword);
+            var pairs = FormPairs(text);
+
+            var data = new StringBuilder(32);
+            
+            foreach (var pair in pairs) {
+                var idx1 = FindCharIndex(ref keyTable, pair[0]);
+                var idx2 = FindCharIndex(ref keyTable, pair[1]);
+
+                var x1 = idx1 / 5;  // x for rows
+                var y1 = idx1 % 5;  // and y for cols
+                var x2 = idx2 / 5;
+                var y2 = idx2 % 5;
+
+                char c1, c2;
+                if (y1 == y2) {
+                    c1 = keyTable[WrapIndex(x1 - 1), y1];
+                    c2 = keyTable[WrapIndex(x2 - 1), y1];
+                }
+                else if (x1 == x2) {
+                    c1 = keyTable[x1, WrapIndex(y1 - 1)];
+                    c2 = keyTable[x1, WrapIndex(y2 - 1)];
+                }
+                else {
+                    c1 = keyTable[x1, y2];
+                    c2 = keyTable[x2, y1];
+                }
+                
+                data.Append(c1).Append(c2);
+            }
+
+            return data.ToString();
+        }
+
+        private char[,] GenerateTable(string keyword) {
+            char[,] table = new char[5,5];
+
+            keyword = ClearKeyword(keyword);
+            for (var i = 0; i < keyword.Length; i++) {
+                table[i / 5,i % 5] = keyword[i];
+            }
+
+            var kwcSet = new HashSet<char>(keyword);
+            var autoAlphabet = EnAlphabet.Except(kwcSet).ToList();
+            for (var i = keyword.Length; i < 25; i++) {
+                table[i / 5,i % 5] = autoAlphabet[i-keyword.Length];
+            }
+
+            return table;
+        }
+
+        private static string ClearKeyword(string keyword) {
+            string data = "";
+
+            keyword = keyword.Replace("J", "I");
+            foreach (var kwc in keyword) {
+                if (!EnAlphabet.Contains(kwc) || kwc == ' ' || data.Contains(kwc)) {
+                    continue;
+                }
+
+                data += kwc;
+            }
+
+            return data;
+        }
+
+        private static int FindCharIndex(ref char[,] table, char c) {
+            for (var i = 0; i < 25; i++) {
+                if (table[i / 5, i % 5] == c) {
+                    return i;
+                }
+            }
+
+            throw new ArgumentOutOfRangeException($"Character '{c}' not fount in table");
+        }
+
+        private static List<string> FormPairs(string text) {
+            List<string> data = new ();
+
+            text = text.Replace("J", "I");
+            var cc = text[0];
+            for (var i = 1; i < text.Length; i++) {
+                if (cc != '\0' && !EnAlphabet.Contains(cc)) {
+                    cc = '\0';
+                }
+                if (cc == '\0') {
+                    cc = text[i];
+                }
+                else if (cc == text[i]) {
+                    data.Add("" + cc + "X");
+                    cc = text[i];
+                }
+                else {
+                    data.Add("" + cc + text[i]);
+                    cc = '\0';
+                }
+            }
+
+            if (cc != '\0') {
+                data.Add("" + cc + "X");
+            }
+            
+            return data;
+        }
+
+        private static int WrapIndex(int idx) {
+            if (idx < 0) {
+                idx += 5;
+            }
+
+            return idx % 5;
+        }
+    }
+}