fix: withdraw/deposit converts from BZZ (10^16 base units) (#66)

* refactor: added toBZZbaseUnit function

* feat: added utility for attesting value is BZZ convertible to base units

* fix: conversion from 15 to 16 decimal places, added unsafe versions

* refactor: withdraw modal uses the safe conversion from BZZ

* refactor: added BigNumber and Token class to handle BZZ digits correctly

* refactor: extract deposit and withdraw functionality into single modal

* test: added tests for Token

* chore: removed unused component

* chore: addressed PR review, token decimal is now integer 0-18

* chore: added comment to clarify the value restriction on token amount

src/utils/index.ts

@@ -0,0 +1,48 @@
+import { BigNumber } from 'bignumber.js'
+
+/**
+ * @deprecated Should be removed in favour of Token class
+ */
+const BZZ_BASE_UNIT = 1e16
+
+/**
+ * Convert from base units of BZZ token to BZZ
+ * @deprecated This should only be used for displaying values, it's unsafe and should be replaced with Token class
+ *
+ * @param amount Amount in base units of BZZ token
+ *
+ * @returns amount in BZZ
+ */
+export const fromBZZbaseUnit = (amount: number): number => {
+  return amount / BZZ_BASE_UNIT
+}
+
+/**
+ * Test if value is an integer
+ *
+ * @param value Value to be tested if it is an integer
+ *
+ * @returns True if the passed in value is integer
+ */
+export function isInteger(value: unknown): value is BigNumber | bigint {
+  return (BigNumber.isBigNumber(value) && value.isInteger()) || typeof value === 'bigint'
+}
+
+/**
+ *Convert value into a BigNumber if not already
+ *
+ * @param value Value to be converted
+ *
+ * @throws {TypeError} if the value is not convertible to a BigNumber
+ *
+ * @returns BigNumber - but it may still be NaN or Infinite
+ */
+export function makeBigNumber(value: BigNumber | bigint | string): BigNumber | never {
+  if (BigNumber.isBigNumber(value)) return value
+
+  if (typeof value === 'string') return new BigNumber(value)
+
+  if (typeof value === 'bigint') return new BigNumber(value.toString())
+
+  throw new TypeError('Not a BigNumber or BigNumber convertible value')
+}