feat: update SubAccount.formID to handle bigger numbers

packages/ledger-icp/src/account_identifier.spec.ts

@@ -60,6 +60,15 @@ describe("SubAccount", () => {
     expect(SubAccount.fromID(1)).toEqual(SubAccount.fromBytes(bytes));
     bytes[31] = 255;
     expect(SubAccount.fromID(255)).toEqual(SubAccount.fromBytes(bytes));
+
+    // Number 18791 in big endian 32 bytes
+    const numberInBytes = [
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+      0, 0, 0, 0, 0, 73, 103,
+    ];
+    expect(SubAccount.fromID(18791)).toEqual(
+      SubAccount.fromBytes(new Uint8Array(numberInBytes)),
+    );
   });
 
   it("throws an exception if initialized with an ID < 0", () => {
@@ -68,9 +77,9 @@ describe("SubAccount", () => {
     }).toThrow();
   });
 
-  it("throws an exception if initialized with an ID > 255", () => {
+  it("throws an exception if initialized with an ID > max int", () => {
     expect(() => {
-      SubAccount.fromID(256);
+      SubAccount.fromID(Number.MAX_SAFE_INTEGER + 1);
     }).toThrow();
   });
 });

packages/ledger-icp/src/account_identifier.ts

@@ -97,12 +97,18 @@ export class SubAccount {
   }
 
   public static fromID(id: number): SubAccount {
-    if (id < 0 || id > 255) {
-      throw "Subaccount ID must be >= 0 and <= 255";
+    if (id < 0) throw new Error("Number cannot be negative");
+
+    if (id > Number.MAX_SAFE_INTEGER) {
+      throw new Error("Number is too large to fit in 32 bytes.");
     }
 
-    const bytes: Uint8Array = new Uint8Array(32).fill(0);
-    bytes[31] = id;
+    const buffer = Buffer.alloc(32);
+
+    // Using 24 as the offset since BigInt64BE uses 8 bytes
+    buffer.writeBigInt64BE(BigInt(id), 24);
+
+    const bytes = new Uint8Array(buffer);
     return new SubAccount(bytes);
   }