Precision from contract (#78)

* Test cases for new precision for @tokenAmount #77 * Implement new @tokenAmount logic. Fixes #77
aragon · Sep 18, 2019 · 35a446d · 35a446d
1 parent d49ddba
commit 35a446d
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Showing 3 changed files with 36 additions and 10 deletions.
diff --git a/src/helpers/lib/formatBN.js b/src/helpers/lib/formatBN.js
@@ -4,18 +4,25 @@ export const tenPow = x => (
   (new BN(10)).pow(new BN(x))
 )
 
-export const formatBN = (amount, base, precision) => {
+export const formatBN = (amount, base, precision, fixed = false) => {
   // Inspired by: https://github.com/ethjs/ethjs-unit/blob/35d870eae1c32c652da88837a71e252a63a83ebb/src/index.js#L83
   const baseLength = base.toString().length
 
   const whole = amount.div(base).toString()
   let fraction = amount.mod(base).toString()
   const zeros = '0'.repeat(Math.max(0, baseLength - fraction.length - 1))
-  fraction = `${zeros}${fraction}`.replace(/0+$/, '').slice(0, precision)
 
-  if (fraction === '' || parseInt(fraction, 10) === 0) {
+  fraction = `${zeros}${fraction}`
+
+  if (!fixed) fraction = fraction.replace(/0+$/, '')
+
+  const slicedFraction = fraction.slice(0, precision)
+
+  if (!fixed && (slicedFraction === '' || parseInt(slicedFraction, 10) === 0)) {
     return whole
   }
 
-  return `${whole}.${fraction}`
+  const prefix = (new BN(slicedFraction).eq(new BN(fraction)) || !fixed) ? '' : '~'
+
+  return `${prefix}${whole}.${slicedFraction}`
 }
diff --git a/src/helpers/tokenAmount.js b/src/helpers/tokenAmount.js
@@ -10,11 +10,12 @@ export default (eth) =>
    * @param {string} tokenAddress The address of the token
    * @param {*} amount The absolute amount for the token quantity (wei)
    * @param {bool} showSymbol Whether the token symbol will be printed after the amount
-   * @param {*} [precision=2] The number of decimal places to format to
+   * @param {*} precision The number of decimal places to format to. If set, the precision is always enforced.
    * @return {Promise<radspec/evaluator/TypedValue>}
    */
-  async (tokenAddress, amount, showSymbol = true, precision = 2) => {
+  async (tokenAddress, amount, showSymbol = true, precision) => {
     const amountBn = new BN(amount)
+    const fixed = !!precision
 
     let decimals
     let symbol
@@ -40,7 +41,9 @@ export default (eth) =>
       }
     }
 
-    const formattedAmount = formatBN(amountBn, tenPow(decimals), Number(precision))
+    precision = precision || decimals
+
+    const formattedAmount = formatBN(amountBn, tenPow(decimals), Number(precision), fixed)
 
     return {
       type: 'string',

diff --git a/test/examples/examples.js b/test/examples/examples.js
@@ -110,15 +110,15 @@ const helperCases = [
   [{
     source: 'Balance: `@tokenAmount(token, balance, false, 5)` ANT',
     bindings: { token: address('0x960b236A07cf122663c4303350609A66A7B288C0'), balance: int('647413054595780000000000') }
-  }, 'Balance: 647413.05459 ANT'],
+  }, 'Balance: ~647413.05459 ANT'],
   [{
     source: 'Balance: `@tokenAmount(token, balance, false, 5)` ANT (non-checksummed)',
     bindings: { token: address('0x960b236a07cf122663c4303350609a66a7b288c0'), balance: int('647413054595780000000000') }
-  }, 'Balance: 647413.05459 ANT (non-checksummed)'],
+  }, 'Balance: ~647413.05459 ANT (non-checksummed)'],
   [{
     source: 'Balance: `@tokenAmount(token, balance)`',
     bindings: { token: address(ETH), balance: int('647413054595780000000000') }
-  }, 'Balance: 647413.05 ETH'],
+  }, 'Balance: 647413.05459578 ETH'],
   [{
     source: 'Balance: `@tokenAmount(token, balance)`',
     bindings: { token: address('0x89205A3A3b2A69De6Dbf7f01ED13B2108B2c43e7'), balance: int('10') }
@@ -127,6 +127,22 @@ const helperCases = [
     source: 'Balance: `@tokenAmount(token, balance)`',
     bindings: { token: address('0x89d24a6b4ccb1b6faa2625fe562bdd9a23260359'), balance: int('10000000000000000000') }
   }, 'Balance: 10 DAI'],
+  [{
+    source: 'Balance: `@tokenAmount(token, balance)`',
+    bindings: { token: address('0x89d24a6b4ccb1b6faa2625fe562bdd9a23260359'), balance: int('1000000000000000') }
+  }, 'Balance: 0.001 DAI'],
+  [{
+    source: 'Balance: `@tokenAmount(token, balance)`',
+    bindings: { token: address('0x89d24a6b4ccb1b6faa2625fe562bdd9a23260359'), balance: int('1') }
+  }, 'Balance: 0.000000000000000001 DAI'],
+  [{
+    source: 'Balance: `@tokenAmount(token, balance, true, 3)`',
+    bindings: { token: address('0x89d24a6b4ccb1b6faa2625fe562bdd9a23260359'), balance: int('1000000000000000001') }
+  }, 'Balance: ~1.000 DAI'],
+  [{
+    source: 'Balance: `@tokenAmount(token, balance)`',
+    bindings: { token: address('0x89d24a6b4ccb1b6faa2625fe562bdd9a23260359'), balance: int('1000000000000000001') }
+  }, 'Balance: 1.000000000000000001 DAI'],
   [{
     source: 'Balance: `@tokenAmount(self.token(): address, balance)`',
     bindings: { balance: int('10000000000000000000') },