From 6b6066fe1edbfd6a94930ec6cd2ecdd23e4537e7 Mon Sep 17 00:00:00 2001
From: pinpong <o.nitzschke@gmail.com>
Date: Thu, 1 Dec 2016 21:07:29 +0100
Subject: [PATCH] implemented toTrytes and toStrings

---
 src/main/java/jota/utils/TrytesConverter.java | 92 +++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 src/main/java/jota/utils/TrytesConverter.java

diff --git a/src/main/java/jota/utils/TrytesConverter.java b/src/main/java/jota/utils/TrytesConverter.java
new file mode 100644
index 0000000..3f90cbd
--- /dev/null
+++ b/src/main/java/jota/utils/TrytesConverter.java
@@ -0,0 +1,92 @@
+package jota.utils;
+
+/**
+ * Created by pinpong on 01.12.16.
+ */
+public class TrytesConverter {
+
+    private static final String TRYTE_ALPHABET = "9ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+
+    /**
+     * Conversion of ascii encoded bytes to trytes.
+     * Input is a string (can be stringified JSON object), return value is Trytes
+     * <p>
+     * How the conversion works:
+     * 2 Trytes === 1 Byte
+     * There are a total of 27 different tryte values: 9ABCDEFGHIJKLMNOPQRSTUVWXYZ
+     * <p>
+     * 1. We get the decimal value of an individual ASCII character
+     * 2. From the decimal value, we then derive the two tryte values by basically calculating the tryte equivalent (e.g. 100 === 19 + 3 * 27)
+     * a. The first tryte value is the decimal value modulo 27 (27 trytes)
+     * b. The second value is the remainder (decimal value - first value), divided by 27
+     * 3. The two values returned from Step 2. are then input as indices into the available values list ('9ABCDEFGHIJKLMNOPQRSTUVWXYZ') to get the correct tryte value
+     * <p>
+     * EXAMPLES
+     * Lets say we want to convert the ASCII character "Z".
+     * 1. 'Z' has a decimal value of 90.
+     * 2. 90 can be represented as 9 + 3 * 27. To make it simpler:
+     * a. First value: 90 modulo 27 is 9. This is now our first value
+     * b. Second value: (90 - 9) / 27 is 3. This is our second value.
+     * 3. Our two values are now 9 and 3. To get the tryte value now we simply insert it as indices into '9ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+     * a. The first tryte value is '9ABCDEFGHIJKLMNOPQRSTUVWXYZ'[9] === "I"
+     * b. The second tryte value is '9ABCDEFGHIJKLMNOPQRSTUVWXYZ'[3] === "C"
+     * Our tryte pair is "IC"
+     * <p>
+     * RESULT:
+     * The ASCII char "Z" is represented as "IC" in trytes.
+     */
+
+    public static String toTrytes(String inputString) {
+
+        String trytes = "";
+
+        for (int i = 0; i < inputString.length(); i++) {
+
+            char asciiValue = inputString.charAt(i);
+
+            // If not recognizable ASCII character, replace with space
+            if (asciiValue > 255) {
+                asciiValue = 32;
+            }
+
+            int firstValue = asciiValue % 27;
+            int secondValue = (asciiValue - firstValue) / 27;
+
+            String trytesValue = String.valueOf(TRYTE_ALPHABET.charAt(firstValue) + String.valueOf(TRYTE_ALPHABET.charAt(secondValue)));
+
+            trytes += trytesValue;
+        }
+
+        return trytes;
+    }
+
+    /**
+     * Trytes to bytes
+     * Reverse operation from the byteToTrytes function in send.js
+     * 2 Trytes == 1 Byte
+     * We assume that the trytes are a JSON encoded object thus for our encoding:
+     * First character = {
+     * Last character = }
+     * Everything after that is 9's padding
+     */
+
+    public static String toString(String inputTrytes) {
+
+        String string = "";
+
+        for (int i = 0; i < inputTrytes.length(); i += 2) {
+            // get a trytes pair
+
+            int firstValue = TRYTE_ALPHABET.indexOf(inputTrytes.charAt(i));
+            int secondValue = TRYTE_ALPHABET.indexOf(inputTrytes.charAt(i + 1));
+
+            int decimalValue = firstValue + secondValue * 27;
+
+            String character = Character.toString((char) decimalValue);
+
+            string += character;
+        }
+
+        return string;
+    }
+}