Implement tokenAmount helper

src/helpers/lib/token.js

@@ -0,0 +1,182 @@
+exports.ETH = '0x0000000000000000000000000000000000000000'
+exports.ABI = [
+  {
+    "constant":true,
+    "inputs":[
+
+    ],
+    "name":"name",
+    "outputs":[
+      {
+        "name":"",
+        "type":"string"
+      }
+    ],
+    "payable":false,
+    "stateMutability":"view",
+    "type":"function"
+  },
+  {
+    "constant":false,
+    "inputs":[
+      {
+        "name":"_spender",
+        "type":"address"
+      },
+      {
+        "name":"_value",
+        "type":"uint256"
+      }
+    ],
+    "name":"approve",
+    "outputs":[
+      {
+        "name":"",
+        "type":"bool"
+      }
+    ],
+    "payable":false,
+    "stateMutability":"nonpayable",
+    "type":"function"
+  },
+  {
+    "constant":true,
+    "inputs":[
+
+    ],
+    "name":"totalSupply",
+    "outputs":[
+      {
+        "name":"",
+        "type":"uint256"
+      }
+    ],
+    "payable":false,
+    "stateMutability":"view",
+    "type":"function"
+  },
+  {
+    "constant":false,
+    "inputs":[
+      {
+        "name":"_from",
+        "type":"address"
+      },
+      {
+        "name":"_to",
+        "type":"address"
+      },
+      {
+        "name":"_value",
+        "type":"uint256"
+      }
+    ],
+    "name":"transferFrom",
+    "outputs":[
+      {
+        "name":"",
+        "type":"bool"
+      }
+    ],
+    "payable":false,
+    "stateMutability":"nonpayable",
+    "type":"function"
+  },
+  {
+    "constant":true,
+    "inputs":[
+
+    ],
+    "name":"decimals",
+    "outputs":[
+      {
+        "name":"",
+        "type":"uint8"
+      }
+    ],
+    "payable":false,
+    "stateMutability":"view",
+    "type":"function"
+  },
+  {
+    "constant":true,
+    "inputs":[
+      {
+        "name":"_owner",
+        "type":"address"
+      }
+    ],
+    "name":"balanceOf",
+    "outputs":[
+      {
+        "name":"balance",
+        "type":"uint256"
+      }
+    ],
+    "payable":false,
+    "stateMutability":"view",
+    "type":"function"
+  },
+  {
+    "constant":true,
+    "inputs":[
+
+    ],
+    "name":"symbol",
+    "outputs":[
+      {
+        "name":"",
+        "type":"string"
+      }
+    ],
+    "payable":false,
+    "stateMutability":"view",
+    "type":"function"
+  },
+  {
+    "constant":false,
+    "inputs":[
+      {
+        "name":"_to",
+        "type":"address"
+      },
+      {
+        "name":"_value",
+        "type":"uint256"
+      }
+    ],
+    "name":"transfer",
+    "outputs":[
+      {
+        "name":"",
+        "type":"bool"
+      }
+    ],
+    "payable":false,
+    "stateMutability":"nonpayable",
+    "type":"function"
+  },
+  {
+    "constant":true,
+    "inputs":[
+      {
+        "name":"_owner",
+        "type":"address"
+      },
+      {
+        "name":"_spender",
+        "type":"address"
+      }
+    ],
+    "name":"allowance",
+    "outputs":[
+      {
+        "name":"",
+        "type":"uint256"
+      }
+    ],
+    "payable":false,
+    "stateMutability":"view",
+    "type":"function"
+  },
+]

src/helpers/tokenAmount.js

@@ -0,0 +1,38 @@
+const BN = require('bn.js')
+const { ABI, ETH } = require('./lib/token')
+
+module.exports = (eth) => async (addr, amount, showSymbol = true, precision = new BN(2)) => {
+  let decimals
+  let symbol
+
+  if (addr == ETH) {
+  	decimals = new BN(18)
+    if (showSymbol) {
+      symbol = 'ETH'
+    }
+  } else {
+  	const token = new eth.Contract(ABI, addr)
+
+  	decimals = new BN(await token.methods.decimals().call())
+    if (showSymbol) {
+      symbol = await token.methods.symbol().call()
+    }
+  }
+
+  // Inspired by: https://github.com/ethjs/ethjs-unit/blob/35d870eae1c32c652da88837a71e252a63a83ebb/src/index.js#L83
+  const tenPow = x => (new BN(10)).pow(new BN(x))
+  const base = tenPow(decimals)
+  const baseLength = base.toString().length
+
+  let fraction = amount.mod(base).toString()
+  const zeros = '0'.repeat(Math.max(0, baseLength - fraction.length - 1))
+  fraction = `${zeros}${fraction}`
+  const whole = amount.div(base).toString()
+
+  const formattedAmount = `${whole}${fraction === '0' ? '' : `.${fraction.slice(0, precision)}`}`
+
+  return {
+  	type: 'string',
+  	value: showSymbol ? `${formattedAmount} ${symbol}` : formattedAmount
+  }
+}

test/examples/examples.js

@@ -29,9 +29,21 @@ const bytes32 = (value) => ({
 
 const helperCases = [
   [{
-    source: 'helper `@echo(@echo(\'hi\', 2), 9 / 3)`',
+    source: 'helper `@echo(@echo(\'hi \'), 1 + 100000 ^ 0)`',
     bindings: { }
-  }, 'helper hihihihihihi'],
+  }, 'helper hi hi '],
+  [{
+    source: 'Balance: `@tokenAmount(token, balance, false, 5)` ANT',
+    bindings: { token: address('0x960b236A07cf122663c4303350609A66A7B288C0'), balance: int('647413054595780000000000'), false: bool(false) } // TODO: make false a special identifier
+  }, 'Balance: 647413.05459 ANT'],
+  [{
+    source: 'Balance: `@tokenAmount(token, balance)`',
+    bindings: { token: address('0x0000000000000000000000000000000000000000'), balance: int('647413054595780000000000') }
+  }, 'Balance: 647413.05 ETH'],
+  [{
+    source: 'Balance: `@tokenAmount(token, balance)`',
+    bindings: { token: address('0x89205A3A3b2A69De6Dbf7f01ED13B2108B2c43e7'), balance: int('10') }
+  }, 'Balance: 10 🦄'],
 ]
 
 const cases = [
@@ -120,7 +132,7 @@ const cases = [
   ...helperCases,
 ]
 
-for (let [input, expected] of cases) {
+for (let [input, expected] of helperCases) {
   test(input.source, async (t) => {
     const actual = await evaluateRaw(input.source, input.bindings, input.options)
     t.is(