feat: add mac import option and help text

src/util/MMKVParser.ts

@@ -0,0 +1,95 @@
+const textDecoder = new TextDecoder('utf-8', { ignoreBOM: true });
+
+export class MMKVParser {
+  private offset = 8;
+  private length: number;
+
+  constructor(private view: DataView) {
+    const payloadLength = view.getUint32(0, true);
+    this.length = 4 + payloadLength;
+  }
+
+  toString() {
+    const offset = this.offset.toString(16).padStart(8, '0');
+    const length = this.length.toString(16).padStart(8, '0');
+    return `<MMKVParser offset=0x${offset} len=0x${length}>`;
+  }
+
+  get eof() {
+    return this.offset >= this.length;
+  }
+
+  peek() {
+    return this.view.getUint8(this.offset);
+  }
+
+  public readByte() {
+    return this.view.getUint8(this.offset++);
+  }
+
+  public readBigInt() {
+    let value = 0n;
+    let shift = 0n;
+
+    let b: number;
+    do {
+      b = this.readByte();
+      value |= BigInt(b & 0x7f) << shift;
+      shift += 7n;
+    } while ((b & 0x80) !== 0);
+
+    return value;
+  }
+
+  public readInt() {
+    const value = this.readBigInt();
+
+    if (value > Number.MAX_SAFE_INTEGER) {
+      throw new Error('Runtime Error: BigInt too large to cast as number');
+    }
+
+    return Number(value);
+  }
+
+  public readBytes(n: number) {
+    const offset = this.offset;
+    const end = offset + n;
+    this.offset = end;
+    return new Uint8Array(this.view.buffer.slice(offset, end));
+  }
+
+  public readString() {
+    // String [
+    //   len: int,
+    //   data: byte[int], # utf-8
+    // ]
+    const strByteLen = this.readInt();
+    const data = this.readBytes(strByteLen);
+    return textDecoder.decode(data).normalize();
+  }
+
+  public readVariantString() {
+    // Container [
+    //   len: int,
+    //   data: variant
+    // ]
+    const containerLen = this.readInt();
+    const newOffset = this.offset + containerLen;
+    const result = this.readString();
+    if (newOffset !== this.offset) {
+      throw new Error('readVariantString failed: offset does not match');
+    }
+    return result;
+  }
+
+  public static toStringMap(view: DataView): Map<string, string> {
+    const mmkv = new MMKVParser(view);
+    const result = new Map<string, string>();
+    while (!mmkv.eof) {
+      const key = mmkv.readString();
+      const value = mmkv.readVariantString();
+      result.set(key, value);
+    }
+    return result;
+  }
+}