implement block timestamp helper functions

src/helpers/blockTime.js

@@ -0,0 +1,23 @@
+import { format } from 'date-fns'
+const MILLISECONDS_IN_A_SECOND = 1000
+
+export default (eth) =>
+  async (blockNumber, showBlock = true, averageBlockTime = 15, formatString = 'yyyy-MM-dd', dateFmtOptions = {}) => {
+    const { number: currentBlock, timestamp: currentTimestamp } = await eth.getBlock('latest')
+    const futureBlock = currentBlock < blockNumber
+    let rawTimestamp
+
+    if (!futureBlock) {
+      rawTimestamp = (await eth.getBlock(blockNumber)).timestamp * MILLISECONDS_IN_A_SECOND
+    } else {
+      const blockDuration = (blockNumber - currentBlock) * averageBlockTime
+      rawTimestamp = (currentTimestamp + blockDuration) * MILLISECONDS_IN_A_SECOND
+    }
+
+    const formattedTime = format(rawTimestamp, formatString, dateFmtOptions)
+
+    return {
+      type: 'string',
+      value: `${formattedTime}${futureBlock ? ' (estimated)' : ''}${showBlock ? ` (block number: ${blockNumber})` : ''}`
+    }
+  }

src/helpers/index.js

@@ -1,31 +1,37 @@
 import HelperManager from './HelperManager'
+import blockTime from './blockTime'
 import echo from './echo'
 import formatDate from './formatDate'
 import fromHex from './fromHex'
 import formatPct from './formatPct'
+import isBlockMined from './isBlockMined'
+import radspec from './radspec'
 import tokenAmount from './tokenAmount'
 import transformTime from './transformTime'
-import radspec from './radspec'
 
 const defaultHelpers = {
+  blockTime,
+  echo,
   formatDate,
-  transformTime,
-  tokenAmount,
   formatPct,
   fromHex,
+  isBlockMined,
   radspec,
-  echo
+  tokenAmount,
+  transformTime
 }
 
 export {
   HelperManager,
   defaultHelpers,
 
+  blockTime,
   echo,
   formatDate,
   formatPct,
   fromHex,
+  isBlockMined,
   radspec,
-  transformTime,
-  tokenAmount
+  tokenAmount,
+  transformTime
 }

src/helpers/isBlockMined.js

@@ -0,0 +1,8 @@
+export default (eth) =>
+  async (blockNumber) => {
+    const { number: currentBlock } = await eth.getBlock('latest')
+    return {
+      type: 'bool',
+      value: currentBlock >= blockNumber
+    }
+  }

test/examples/examples.js

@@ -207,7 +207,19 @@ const helperCases = [
     source: 'Bar `@bar(shift)` foo `@foo(n)`',
     bindings: { shift: bool(true), n: int(7) },
     options: { userHelpers: { bar: () => shift => ({ type: 'string', value: shift ? 'BAR' : 'bar' }), foo: () => n => ({ type: 'number', value: n * 7 }) } }
-  }, 'Bar BAR foo 49']
+  }, 'Bar BAR foo 49'],
+  [{
+    source: 'get a past date: `@blockTime(block, showBlock)`',
+    bindings: { block: int('8765432'), showBlock: bool(false) }
+  }, 'get a past date: 2019-10-18'],
+  [{
+    source: 'get a past date: `@blockTime(block, showBlock)`',
+    bindings: { block: int('8765432'), showBlock: bool(true) }
+  }, 'get a past date: 2019-10-18 (block number: 8765432)'],
+  [{
+    source: 'See if block is mined: `@isBlockMined(block)`',
+    bindings: { block: int('98765430') }
+  }, 'See if block is mined: false']
 ]
 
 const dataDecodeCases = [
@@ -430,3 +442,33 @@ cases.forEach(([input, expected], index) => {
     )
   })
 })
+
+const fuzzyCases = [
+  [{
+    source: 'Get a future date: `@blockTime(block)`',
+    bindings: { block: int('20976543') }
+  }, /^Get a future date: 202\d(?:-\d\d){2} \(estimated\) \(block number: 20976543\)$/],
+  [{
+    source: 'Get a future date without showing block number: `@blockTime(block, false)`',
+    bindings: { block: int('20976543') }
+  }, /^Get a future date without showing block number: 202\d(?:-\d\d){2} \(estimated\)$/]
+]
+
+fuzzyCases.forEach(([input, regExp], index) => {
+  test(`${index} - ${input.source}`, async (t) => {
+    const { userHelpers } = input.options || {}
+    const actual = await evaluateRaw(
+      input.source,
+      input.bindings,
+      {
+        ...input.options,
+        availableHelpers: { ...defaultHelpers, ...userHelpers }
+      }
+    )
+    t.regex(
+      actual,
+      regExp,
+      `Expected "${input.source}" to match "${regExp}", but evaluated to "${actual}"`
+    )
+  })
+})