Created CameraPathValidator to validate Camera Paths before playing them and uses its static validateCameraPath() method whenever a Camera Path is to be started

Camera Paths can't start if negative movement through time would be required

src/main/java/eu/crushedpixel/replaymod/utils/CameraPathValidator.java

@@ -0,0 +1,41 @@
+package eu.crushedpixel.replaymod.utils;
+
+import eu.crushedpixel.replaymod.ReplayMod;
+import eu.crushedpixel.replaymod.chat.ChatMessageHandler;
+import eu.crushedpixel.replaymod.holders.AdvancedPosition;
+import eu.crushedpixel.replaymod.holders.Keyframe;
+import eu.crushedpixel.replaymod.holders.TimestampValue;
+import eu.crushedpixel.replaymod.interpolation.KeyframeList;
+import net.minecraft.client.resources.I18n;
+
+public class CameraPathValidator {
+
+    public static class InvalidCameraPathException extends Exception {
+        public InvalidCameraPathException(String message) {
+            super(message);
+        }
+
+        @Override
+        public String getLocalizedMessage() {
+            return I18n.format(getMessage());
+        }
+
+        public void printToChat() {
+            ReplayMod.chatMessageHandler.addLocalizedChatMessage(getMessage(), ChatMessageHandler.ChatMessageType.WARNING);
+        }
+    }
+
+    public static void validateCameraPath(KeyframeList<AdvancedPosition> positionKeyframes, KeyframeList<TimestampValue> timeKeyframes)
+            throws InvalidCameraPathException {
+
+        if(positionKeyframes.size() < 2 || timeKeyframes.size() < 2) {
+            throw new InvalidCameraPathException("replaymod.chat.morekeyframes");
+        }
+
+        int previousTimestamp = -1;
+        for(Keyframe<TimestampValue> timeKeyframe : timeKeyframes) {
+            if(timeKeyframe.getValue().asInt() < previousTimestamp) throw new InvalidCameraPathException("replaymod.chat.negativetime");
+            previousTimestamp = timeKeyframe.getValue().asInt();
+        }
+    }
+}