Adding b64 and json decoder and encoder functions (#829)

docs/scarpet/language/FunctionsAndControlFlow.md

@@ -267,6 +267,7 @@ but like everywhere else, doing that sounds like a bad idea.
   - `io_exception`: This is the parent for any exception that occurs due to an error handling external data.
     - `nbt_error`: Incorrect input/output NBT file.
     - `json_error`: Incorrect input/output JSON data.
+    - `b64_error`: Incorrect input/output b64 (base 64) string
   - `user_exception`: Exception thrown by default with `throw` function.
   
 Synopsis:

docs/scarpet/language/LoopsAndHigherOrderFunctions.md

@@ -146,3 +146,12 @@ it will be used from now on as a new value for the accumulator.
 reduce([1,2,3,4],_a+_,0)  => 10
 reduce([1,2,3,4],_a*_,1)  => 24
 </pre>
+
+### `encode_b64(string)`, `decode_b64(string)`
+
+Encode or decode a string from b64, throwing a `b64_error` exception if it's invalid
+
+### `encode_json(value)`, `decode_json(string)`
+
+Encodes a value as a json string, and decodes a json string as a valid value, throwing a `json_error` exception if it 
+doesn't parse properly

src/main/java/carpet/script/exception/Throwables.java

@@ -27,6 +27,7 @@ public class Throwables {
     public static final Throwables IO_EXCEPTION          = register("io_exception", THROWN_EXCEPTION_TYPE);
     public static final Throwables NBT_ERROR             = register("nbt_error", IO_EXCEPTION);
     public static final Throwables JSON_ERROR            = register("json_error", IO_EXCEPTION);
+    public static final Throwables B64_ERROR             = register("b64_error", IO_EXCEPTION);
     public static final Throwables USER_DEFINED          = register("user_exception", THROWN_EXCEPTION_TYPE);
 
     /**

src/main/java/carpet/script/language/DataStructures.java

@@ -4,6 +4,9 @@ import carpet.script.Context;
 import carpet.script.Expression;
 import carpet.script.LazyValue;
 import carpet.script.exception.InternalExpressionException;
+import carpet.script.exception.ThrowStatement;
+import carpet.script.exception.Throwables;
+import carpet.script.utils.ScarpetJsonDeserializer;
 import carpet.script.value.ContainerValueInterface;
 import carpet.script.value.LContainerValue;
 import carpet.script.value.LazyListValue;
@@ -12,8 +15,12 @@ import carpet.script.value.MapValue;
 import carpet.script.value.NumericValue;
 import carpet.script.value.StringValue;
 import carpet.script.value.Value;
+import com.google.gson.JsonParseException;
+import com.google.gson.JsonParser;
 
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
+import java.util.Base64;
 import java.util.Collections;
 import java.util.List;
 import java.util.stream.Collectors;
@@ -320,5 +327,23 @@ public class DataStructures {
             Value ret = new NumericValue(((ContainerValueInterface) container).delete(lv.get(lv.size()-1).evalValue(c)));
             return (cc, tt) -> ret;
         });
+
+        expression.addUnaryFunction("encode_b64", v -> StringValue.of(Base64.getEncoder().encodeToString(v.getString().getBytes())));
+        expression.addUnaryFunction("decode_b64", v -> {
+            try {
+                return StringValue.of(new String(Base64.getDecoder().decode(v.getString()), StandardCharsets.ISO_8859_1));//using this charset cos it's the one used in decoding function
+            } catch (IllegalArgumentException iae){
+                throw new ThrowStatement("Invalid b64 string: " + v.getString(), Throwables.B64_ERROR);
+            }
+        });
+
+        expression.addUnaryFunction("encode_json", v -> StringValue.of(v.toJson().toString()));
+        expression.addUnaryFunction("decode_json", v -> {
+            try {
+                return new ScarpetJsonDeserializer().deserialize(new JsonParser().parse(v.getString()), null, null);
+            } catch (JsonParseException jpe){
+                throw new ThrowStatement("Invalid json string: " + v.getString(), Throwables.JSON_ERROR);
+            }
+        });
     }
 }