Read Reviver

I still need to implement `this` calling.

```js
JSON.parse('{ "heya": ["nice", "2342"] }', (key, value) => { console.log(key, value); return Array.isArray(value) && value[0] === "nice" ? BigInt(value[1]) : value });
```

#33

src/read.ts

@@ -16,12 +16,14 @@ export interface ReadOptions {
   rootCheck: boolean;
 }
 
+export type Reviver = (this: any, key: any, value: any) => Tag;
+
 /**
  * Converts an NBT buffer into an NBT object. Accepts an endian type, compression format, and file headers to read the data with.
  * 
  * If a format option isn't specified, the function will attempt reading the data using all options until it either throws or returns successfully.
 */
-export async function read<T extends RootTagLike = RootTag>(data: Uint8Array | ArrayBufferLike | Blob, options: Partial<ReadOptions> = {}): Promise<NBTData<T>> {
+export async function read<T extends RootTagLike = RootTag>(data: Uint8Array | ArrayBufferLike | Blob, options: Partial<ReadOptions> = {}, reviver?: Reviver): Promise<NBTData<T>> {
   if (data instanceof Blob) {
     data = await data.arrayBuffer();
   }
@@ -65,10 +67,10 @@ export async function read<T extends RootTagLike = RootTag>(data: Uint8Array | A
       case reader.hasZlibHeader(): compression = "deflate"; break compression;
     }
     try {
-      return await read<T>(data, { ...options, compression: null });
+      return await read<T>(data, { ...options, compression: null }, reviver);
     } catch (error) {
       try {
-        return await read<T>(data, { ...options, compression: "deflate-raw" });
+        return await read<T>(data, { ...options, compression: "deflate-raw" }, reviver);
       } catch {
         throw error;
       }
@@ -79,13 +81,13 @@ export async function read<T extends RootTagLike = RootTag>(data: Uint8Array | A
 
   if (endian === undefined) {
     try {
-      return await read<T>(data, { ...options, endian: "big" });
+      return await read<T>(data, { ...options, endian: "big" }, reviver);
     } catch (error) {
       try {
-        return await read<T>(data, { ...options, endian: "little" });
+        return await read<T>(data, { ...options, endian: "little" }, reviver);
       } catch {
         try {
-          return await read<T>(data, { ...options, endian: "little-varint" });
+          return await read<T>(data, { ...options, endian: "little-varint" }, reviver);
         } catch {
           throw error;
         }
@@ -97,10 +99,10 @@ export async function read<T extends RootTagLike = RootTag>(data: Uint8Array | A
 
   if (rootName === undefined) {
     try {
-      return await read<T>(data, { ...options, rootName: true });
+      return await read<T>(data, { ...options, rootName: true }, reviver);
     } catch (error) {
       try {
-        return await read<T>(data, { ...options, rootName: false });
+        return await read<T>(data, { ...options, rootName: false }, reviver);
       } catch {
         throw error;
       }
@@ -117,7 +119,7 @@ export async function read<T extends RootTagLike = RootTag>(data: Uint8Array | A
     bedrockLevel = reader.hasBedrockLevelHeader(endian);
   }
 
-  return reader.readRoot<T>({ rootName, endian, compression, bedrockLevel, strict, rootCheck });
+  return reader.readRoot<T>({ rootName, endian, compression, bedrockLevel, strict, rootCheck }, reviver);
 }
 
 class NBTReader {
@@ -157,7 +159,7 @@ class NBTReader {
     }
   }
 
-  async readRoot<T extends RootTagLike = RootTag>({ rootName, endian, compression, bedrockLevel, strict, rootCheck }: ReadOptions): Promise<NBTData<T>> {
+  async readRoot<T extends RootTagLike = RootTag>({ rootName, endian, compression, bedrockLevel, strict, rootCheck }: ReadOptions, reviver: Reviver = (_key, value) => value): Promise<NBTData<T>> {
     if (compression !== null) {
       this.#data = await decompress(this.#data, compression);
       this.#view = new DataView(this.#data.buffer);
@@ -179,7 +181,7 @@ class NBTReader {
       throw new Error(`Expected root name '${rootName}', encountered '${rootNameV}'`);
     }
 
-    const root: T = this.#readTag<T>(type);
+    const root: T = reviver("", this.#readTag<T>(type, reviver)) as T;
 
     if (strict && this.#data.byteLength > this.#byteOffset) {
       const remaining: number = this.#data.byteLength - this.#byteOffset;
@@ -195,9 +197,9 @@ class NBTReader {
     return result;
   }
 
-  #readTag<T extends Tag>(type: TAG): T;
-  #readTag<T extends RootTagLike>(type: TAG): T;
-  #readTag(type: TAG): Tag {
+  #readTag<T extends Tag>(type: TAG, reviver: Reviver): T;
+  #readTag<T extends RootTagLike>(type: TAG, reviver: Reviver): T;
+  #readTag(type: TAG, reviver: Reviver): Tag {
     switch (type) {
       case TAG.END: {
         const remaining: number = this.#data.byteLength - this.#byteOffset;
@@ -211,8 +213,8 @@ class NBTReader {
       case TAG.DOUBLE: return this.#readDouble();
       case TAG.BYTE_ARRAY: return this.#readByteArray();
       case TAG.STRING: return this.#readString();
-      case TAG.LIST: return this.#readList();
-      case TAG.COMPOUND: return this.#readCompound();
+      case TAG.LIST: return this.#readList(reviver);
+      case TAG.COMPOUND: return this.#readCompound(reviver);
       case TAG.INT_ARRAY: return this.#readIntArray();
       case TAG.LONG_ARRAY: return this.#readLongArray();
       default: throw new Error(`Encountered unsupported tag type '${type}' at byte offset ${this.#byteOffset}`);
@@ -363,7 +365,7 @@ class NBTReader {
     return value;
   }
 
-  #readList(): ListTag<Tag> {
+  #readList(reviver: Reviver): ListTag<Tag> {
     const type: TAG = this.#readTagType();
     const length: number = this.#varint ? this.#readVarIntZigZag(true) : this.#readInt(true);
     const value: ListTag<Tag> = [];
@@ -374,19 +376,19 @@ class NBTReader {
       value: type
     });
     for (let i: number = 0; i < length; i++) {
-      const entry: Tag = this.#readTag(type);
+      const entry: Tag = reviver(i, this.#readTag(type, reviver));
       value.push(entry);
     }
     return value;
   }
 
-  #readCompound(): CompoundTag {
+  #readCompound(reviver: Reviver): CompoundTag {
     const value: CompoundTag = {};
     while (true) {
       const type: TAG = this.#readTagType();
       if (type === TAG.END) break;
       const name: string = this.#readString();
-      const entry: Tag = this.#readTag(type);
+      const entry: Tag = reviver(name, this.#readTag(type, reviver));
       value[name] = entry;
     }
     return value;