1 files changed, 59 insertions, 0 deletions
diff --git a/app/scripts/lib/nonce-tracker.js b/app/scripts/lib/nonce-tracker.js
new file mode 100644
index 000000000..ab2893b10
--- /dev/null
+++ b/app/scripts/lib/nonce-tracker.js
@@ -0,0 +1,59 @@
+const EthQuery = require('eth-query')
+
+class NonceTracker {
+
+  constructor ({ blockTracker, provider, getPendingTransactions }) {
+    this.blockTracker = blockTracker
+    this.ethQuery = new EthQuery(provider)
+    this.getPendingTransactions = getPendingTransactions
+    this.lockMap = {}
+  }
+
+  // releaseLock must be called
+  // releaseLock must be called after adding signed tx to pending transactions (or discarding)
+  async getNonceLock (address) {
+    // await lock free
+    await this.lockMap[address]
+    // take lock
+    const releaseLock = this._takeLock(address)
+    // calculate next nonce
+    // we need to make sure our base count
+    // and pending count are from the same block
+    const currentBlock = await this._getCurrentBlock()
+    const pendingTransactions = this.getPendingTransactions(address)
+    const baseCount = await this._getTxCount(address, currentBlock)
+    const nextNonce = parseInt(baseCount) + pendingTransactions.length
+    // return next nonce and release cb
+    return { nextNonce: nextNonce.toString(16), releaseLock }
+  }
+
+  async _getCurrentBlock () {
+    const currentBlock = this.blockTracker.getCurrentBlock()
+    if (currentBlock) return currentBlock
+    return await Promise((reject, resolve) => {
+      this.blockTracker.once('latest', resolve)
+    })
+  }
+
+  _takeLock (lockId) {
+    let releaseLock = null
+    // create and store lock
+    const lock = new Promise((resolve, reject) => { releaseLock = resolve })
+    this.lockMap[lockId] = lock
+    // setup lock teardown
+    lock.then(() => delete this.lockMap[lockId])
+    return releaseLock
+  }
+
+  async _getTxCount (address, currentBlock) {
+    const blockNumber = currentBlock.number
+    return new Promise((resolve, reject) => {
+      this.ethQuery.getTransactionCount(address, blockNumber, (err, result) => {
+        err ? reject(err) : resolve(result)
+      })
+    })
+  }
+
+}
+
+module.exports = NonceTracker