From 446d5f23062dd965c0b0409819c0d274a570fa79 Mon Sep 17 00:00:00 2001
From: Hubert Tylkowski <hubert.tylkowski@gmail.com>
Date: Wed, 20 Jun 2018 01:06:07 +0200
Subject: [PATCH] decode added!

---
 Zadanie-03/src/com/tylkowski/crc/CrcTask.java | 61 ++++++++++++++++---
 Zadanie-03/src/com/tylkowski/crc/Main.java    |  1 +
 2 files changed, 53 insertions(+), 9 deletions(-)

diff --git a/Zadanie-03/src/com/tylkowski/crc/CrcTask.java b/Zadanie-03/src/com/tylkowski/crc/CrcTask.java
index 57d2e59..b6c9df4 100644
--- a/Zadanie-03/src/com/tylkowski/crc/CrcTask.java
+++ b/Zadanie-03/src/com/tylkowski/crc/CrcTask.java
@@ -53,7 +53,7 @@ class CrcTask {
                 }
                 short[] remainder = calcXOR(piece, polyGenerator);
                 remainder = removeUnecessaryZeros(remainder);
-                createMessageFromRemainderAndPartFromOldMessage(remainder, remainder.length);
+                messageAsShortArray = createMessageFromRemainderAndPartFromOldMessage(remainder, messageAsShortArray);
             }
 
 
@@ -61,12 +61,13 @@ class CrcTask {
 
     }
 
-    private void createMessageFromRemainderAndPartFromOldMessage(short[] remainder, int length) {
-        short[] tempArr = new short[remainder.length + messageAsShortArray.length - polyGenerator.length];
-        System.arraycopy(remainder, 0, tempArr, 0, length);
+    private short[] createMessageFromRemainderAndPartFromOldMessage(short[] remainder, short[] msg) {
+        short[] tempArr = new short[remainder.length + msg.length - polyGenerator.length];
+        System.arraycopy(remainder, 0, tempArr, 0, remainder.length);
         int diff = polyGenerator.length - remainder.length;
-        System.arraycopy(messageAsShortArray, length + diff, tempArr, length, messageAsShortArray.length - diff - length);
-        messageAsShortArray = tempArr;
+        System.arraycopy(msg, remainder.length + diff, tempArr, remainder.length, msg.length - diff - remainder.length);
+        msg = tempArr;
+        return msg;
     }
 
     private short[] removeUnecessaryZeros(short[] remainder) {
@@ -151,15 +152,57 @@ class CrcTask {
         polyGenerator[16] = 1;
     }
 
-    private void swapPolynomialValues() {
+    private short[] swapPolynomialValues(short[] poly) {
         for (int i = 0; i < polyGenerator.length - 1; i++) {
-            messageAsShortArray[i] = (short) ((messageAsShortArray[i] + 1) % 2);
+            poly[i] = (short) ((poly[i] + 1) % 2);
         }
+        return poly;
     }
 
     String encode() {
         convertMessageToBinaryShortArray();
-        swapPolynomialValues();
+        messageAsShortArray = swapPolynomialValues(messageAsShortArray);
         return rawMessage + generateFCS();
     }
+
+    boolean decode(String encodedString) {
+        encodedString = fillPolyTo8(encodedString);
+        short[] encodedShortArray = convertBinaryStringToShortArray(encodedString);
+        encodedShortArray = swapPolynomialValues(encodedShortArray);
+        while (true) {
+            if (shortArrayContains(encodedShortArray, 1)) {
+                return true;
+            }
+
+            if (encodedShortArray[0] == 0) {
+                encodedShortArray = Arrays.copyOfRange(encodedShortArray, 1, encodedShortArray.length);
+            } else {
+                short[] piece = Arrays.copyOfRange(encodedShortArray, 0, Math.min(polyGenerator.length, encodedShortArray.length));
+                if (piece.length < polyGenerator.length) {
+                    return false;
+                }
+
+                short[] remainder = calcXOR(piece, polyGenerator);
+                remainder = removeUnecessaryZeros(remainder);
+                encodedShortArray = createMessageFromRemainderAndPartFromOldMessage(remainder, encodedShortArray);
+            }
+        }
+    }
+
+    private boolean shortArrayContains(short[] encodedShortArray, int value) {
+        for (short item : encodedShortArray) {
+            if (item == value) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private String fillPolyTo8(String encodedString) {
+        StringBuilder stringBuilder = new StringBuilder(encodedString);
+        while (stringBuilder.length() % 8 != 0) {
+            stringBuilder.insert(0, "0");
+        }
+        return stringBuilder.toString();
+    }
 }
diff --git a/Zadanie-03/src/com/tylkowski/crc/Main.java b/Zadanie-03/src/com/tylkowski/crc/Main.java
index 3cc07b8..77f226e 100644
--- a/Zadanie-03/src/com/tylkowski/crc/Main.java
+++ b/Zadanie-03/src/com/tylkowski/crc/Main.java
@@ -5,6 +5,7 @@ public class Main {
     public static void main(String[] args) {
         CrcTask crcTask = new CrcTask(toBinary(args[0]), args[0]);
         System.out.println(crcTask.encode());
+        System.out.println(crcTask.decode(toBinary(crcTask.encode())));
     }
 
     private static String toBinary(String s) {