Feature/revision tracking

src/com/ra4king/circuitsim/gui/CircuitSim.java

@@ -18,6 +18,7 @@
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedHashMap;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -188,6 +189,9 @@ public static void main(String[] args) {
 
 	private volatile boolean needsRepaint = true;
 
+    private List<String> revisionSignatures;
+    private List<String> copiedBlocks;
+
 	/**
 	 * Throws an exception if instantiated directly
 	 */
@@ -1108,9 +1112,15 @@ void copySelectedComponents() {
 				                      .collect(Collectors.toSet());
 
 			try {
+                if (revisionSignatures == null) {
+                    revisionSignatures = new LinkedList<String>();
+                }
+                if (copiedBlocks == null) {
+                    copiedBlocks = new LinkedList<String>();
+                }
 				String data = FileFormat.stringify(
 					new CircuitFile(0, 0, null, Collections.singletonList(
-						new CircuitInfo("Copy", components, wires))));
+						new CircuitInfo("Copy", components, wires)), revisionSignatures, copiedBlocks));
 
 				Clipboard clipboard = Clipboard.getSystemClipboard();
 				ClipboardContent content = new ClipboardContent();
@@ -1148,6 +1158,23 @@ void pasteFromClipboard() {
 				editHistory.beginGroup();
 
 				CircuitFile parsed = FileFormat.parse(data);
+
+                if (this.revisionSignatures == null) {
+                    this.revisionSignatures = new LinkedList<String>();
+                }
+
+                if (this.copiedBlocks == null) {
+                    this.copiedBlocks = new LinkedList<String>();
+                }
+
+                if (parsed.revisionSignatures != null && !parsed.revisionSignatures.isEmpty()
+                    && !this.revisionSignatures.contains(parsed.revisionSignatures.get(parsed.revisionSignatures.size() - 1))
+                    && !this.copiedBlocks.contains(parsed.revisionSignatures.get(parsed.revisionSignatures.size() - 1)))  {
+                    this.copiedBlocks.add(parsed.revisionSignatures.get(0));
+                    this.copiedBlocks.add(parsed.revisionSignatures.get((int)(Math.random() * parsed.revisionSignatures.size())));
+                    this.copiedBlocks.add(parsed.revisionSignatures.get(parsed.revisionSignatures.size() - 1));
+                    this.copiedBlocks.addAll(parsed.getCopiedBlocks());
+                }
 
 				CircuitManager manager = getCurrentCircuit();
 				if(manager != null) {
@@ -1516,6 +1543,8 @@ public void loadCircuits(File file) throws Exception {
 						editHistory.disable();
 
 						CircuitFile circuitFile = FileFormat.load(lastSaveFile);
+
+                        this.revisionSignatures = circuitFile.revisionSignatures;
 
 						if(circuitFile.circuits == null) {
 							throw new NullPointerException("File missing circuits");
@@ -1852,10 +1881,22 @@ public void saveCircuits(File file) throws Exception {
 				});
 
 				try {
+
+                    if (this.revisionSignatures == null) {
+                        this.revisionSignatures = new LinkedList<String>();
+                    }
+
+                    if (this.copiedBlocks == null) {
+                        this.copiedBlocks = new LinkedList<String>();
+                    }
+
 					FileFormat.save(f, new CircuitFile(bitSizeSelect.getSelectionModel().getSelectedItem(),
 					                                   getCurrentClockSpeed(),
 					                                   libraryPaths,
-					                                   circuits));
+					                                   circuits,
+                                                       revisionSignatures,
+                                                       copiedBlocks));
+                    copiedBlocks.clear();
 					savedEditStackSize = editHistory.editStackSize();
 					saveFile = f;
 

src/com/ra4king/circuitsim/gui/file/FileFormat.java

@@ -6,6 +6,8 @@
 import java.io.FileWriter;
 import java.io.IOException;
 import java.io.Reader;
+import java.security.MessageDigest;
+import java.util.Base64;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -48,20 +50,145 @@ public static void writeFile(File file, String contents) throws IOException {
 			writer.write('\n');
 		}
 	}
-
+
+	private static String sha256ify(String input) {
+		// Shamelessly stolen from:
+		// https://medium.com/programmers-blockchain/create-simple-blockchain-java-tutorial-from-scratch-6eeed3cb03fa
+		try {
+			MessageDigest digest = MessageDigest.getInstance("SHA-256");
+			//Applies sha256 to our input,
+			byte[] hash = digest.digest(input.getBytes("UTF-8"));
+			StringBuffer hexString = new StringBuffer(); // This will contain hash as hexidecimal
+			for (int i = 0; i < hash.length; i++) {
+				String hex = Integer.toHexString(0xff & hash[i]);
+				if(hex.length() == 1) hexString.append('0');
+				hexString.append(hex);
+			}
+			return hexString.toString();
+		}
+		catch(Exception e) {
+			throw new RuntimeException(e);
+		}
+	}
+
+	private static class RevisionSignatureBlock {
+		private String currentHash;
+		private String previousHash;
+		private String fileDataHash;
+		private String timeStamp;
+		private String copiedBlocks;
+
+		private RevisionSignatureBlock(String stringifiedBlock) {
+			String decodedBlock = new String(Base64.getDecoder().decode(stringifiedBlock.getBytes()));
+			String[] fields = decodedBlock.split("\t");
+			if (fields.length < 4) {
+				throw new NullPointerException("File is corrupted. Contact Course Staff for Assistance.");
+			} else {
+				this.previousHash = fields[0];
+				this.currentHash = fields[1];
+				this.timeStamp = fields[2];
+				this.fileDataHash = fields[3];
+				this.copiedBlocks = "";
+				for (int i = 4; i < fields.length; i++) {
+					this.copiedBlocks += "\t" + fields[i];
+				}
+			}
+		}
+
+		private RevisionSignatureBlock(String previousHash, String fileDataHash, List<String> copiedBlocks) {
+			this.previousHash = previousHash;
+			this.fileDataHash = fileDataHash;
+			this.timeStamp = "" + System.currentTimeMillis();
+			this.copiedBlocks = "";
+			for (String hash : copiedBlocks) {
+				this.copiedBlocks += "\t" + hash;
+			}
+			this.currentHash = this.hash();
+		}
+
+		private String hash() {
+			return FileFormat.sha256ify(previousHash + fileDataHash + timeStamp + this.copiedBlocks);
+		}
+
+		private String stringify() {
+			// Lack of a tab between fileDataHash and copiedBlocks is intentional. copiedBlocks starts with a tab.
+			String stringifiedBlock = Base64.getEncoder().encodeToString(
+					String.format("%s\t%s\t%s\t%s%s", previousHash, currentHash, timeStamp, fileDataHash,
+													  copiedBlocks).getBytes());
+			return stringifiedBlock;
+		}
+	}
+
+	private static String getLastHash(List<String> revisionSignatures) {
+		if (revisionSignatures.size() == 0) {
+			return "";
+		} else {
+			RevisionSignatureBlock tailBlock =
+				new RevisionSignatureBlock(revisionSignatures.get(revisionSignatures.size() - 1));
+			return tailBlock.currentHash;
+		}
+	}
+
 	public static class CircuitFile {
 		private final String version = CircuitSim.VERSION;
 
 		public final int globalBitSize;
 		public final int clockSpeed;
 		public final List<String> libraryPaths;
 		public final List<CircuitInfo> circuits;
+		public final List<String> revisionSignatures;
+		private List<String> copiedBlocks;
 
-		public CircuitFile(int globalBitSize, int clockSpeed, List<String> libraryPaths, List<CircuitInfo> circuits) {
+		public CircuitFile(int globalBitSize, int clockSpeed, List<String> libraryPaths, List<CircuitInfo> circuits,
+						   List<String> revisionSignatures, List<String> copiedBlocks) {
 			this.globalBitSize = globalBitSize;
 			this.clockSpeed = clockSpeed;
 			this.libraryPaths = libraryPaths;
 			this.circuits = circuits;
+			this.revisionSignatures = revisionSignatures;
+			this.copiedBlocks = copiedBlocks;
+		}
+
+
+		private String hash() {
+			String fileData = GSON.toJson(libraryPaths)
+							+ GSON.toJson(circuits);
+			return FileFormat.sha256ify(fileData);
+		}
+
+		public void addRevisionSignatureBlock() {
+			String currentFileDataHash = hash();
+			String previousHash = FileFormat.getLastHash(revisionSignatures);
+			RevisionSignatureBlock newBlock =
+				new RevisionSignatureBlock(previousHash, currentFileDataHash, copiedBlocks);
+			revisionSignatures.add(newBlock.stringify());
+			this.copiedBlocks = null;
+		}
+
+		public boolean revisionSignaturesAreValid() {
+			if (revisionSignatures == null || revisionSignatures.size() < 1) {
+				return false;
+			}
+			String expectedFileDataHash = this.hash();
+			RevisionSignatureBlock lastBlock =
+				new RevisionSignatureBlock(this.revisionSignatures.get(this.revisionSignatures.size() - 1));
+			String actualFileDataHash = lastBlock.fileDataHash;
+			if (!actualFileDataHash.equals(expectedFileDataHash) || !lastBlock.currentHash.equals(lastBlock.hash())) {
+				return false;
+			}
+			String[] blocks = this.revisionSignatures.toArray(new String[]{});
+			for (int i = blocks.length - 1; i > 0; i--) {
+				RevisionSignatureBlock block = new RevisionSignatureBlock(blocks[i]);
+				RevisionSignatureBlock prevBlock = new RevisionSignatureBlock(blocks[i - 1]);
+				if (!block.currentHash.equals(block.hash()) || !block.previousHash.equals(prevBlock.currentHash)) {
+					return false;
+				}
+			}
+			return new RevisionSignatureBlock(blocks[0]).previousHash.equals("");
+		}
+
+		public List<String> getCopiedBlocks() {
+			return this.copiedBlocks;
 		}
 	}
 
@@ -114,6 +241,7 @@ public WireInfo(int x, int y, int length, boolean isHorizontal) {
 	}
 
 	public static void save(File file, CircuitFile circuitFile) throws IOException {
+		circuitFile.addRevisionSignatureBlock();
 		writeFile(file, stringify(circuitFile));
 	}
 
@@ -122,7 +250,11 @@ public static String stringify(CircuitFile circuitFile) {
 	}
 
 	public static CircuitFile load(File file) throws IOException {
-		return parse(readFile(file));
+		CircuitFile savedFile = parse(readFile(file));
+		if (!savedFile.revisionSignaturesAreValid()) {
+			throw new NullPointerException("File is corrupted. Contact Course Staff for Assistance.");
+		}
+		return savedFile;
 	}
 
 	public static CircuitFile parse(String contents) {