1 files changed, 64 insertions, 0 deletions
diff --git a/app/scripts/controllers/transactions/lib/tx-state-history-helper.js b/app/scripts/controllers/transactions/lib/tx-state-history-helper.js
new file mode 100644
index 000000000..7a57e3cb5
--- /dev/null
+++ b/app/scripts/controllers/transactions/lib/tx-state-history-helper.js
@@ -0,0 +1,64 @@
+const jsonDiffer = require('fast-json-patch')
+const clone = require('clone')
+/** @module*/
+module.exports = {
+  generateHistoryEntry,
+  replayHistory,
+  snapshotFromTxMeta,
+  migrateFromSnapshotsToDiffs,
+}
+
+/**
+  converts non-initial history entries into diffs
+  @param longHistory {array}
+  @returns {array}
+*/
+function migrateFromSnapshotsToDiffs (longHistory) {
+  return (
+    longHistory
+    // convert non-initial history entries into diffs
+    .map((entry, index) => {
+      if (index === 0) return entry
+      return generateHistoryEntry(longHistory[index - 1], entry)
+    })
+  )
+}
+
+/**
+  generates an array of history objects sense the previous state.
+  The object has the keys opp(the operation preformed),
+  path(the key and if a nested object then each key will be seperated with a `/`)
+  value
+  with the first entry having the note
+  @param previousState {object} - the previous state of the object
+  @param newState {object} - the update object
+  @param note {string} - a optional note for the state change
+  @reurns {array}
+*/
+function generateHistoryEntry (previousState, newState, note) {
+  const entry = jsonDiffer.compare(previousState, newState)
+  // Add a note to the first op, since it breaks if we append it to the entry
+  if (note && entry[0]) entry[0].note = note
+  return entry
+}
+
+/**
+  Recovers previous txMeta state obj
+  @return {object}
+*/
+function replayHistory (_shortHistory) {
+  const shortHistory = clone(_shortHistory)
+  return shortHistory.reduce((val, entry) => jsonDiffer.applyPatch(val, entry).newDocument)
+}
+
+/**
+  @param txMeta {object}
+  @returns {object} a clone object of the txMeta with out history
+*/
+function snapshotFromTxMeta (txMeta) {
+  // create txMeta snapshot for history
+  const snapshot = clone(txMeta)
+  // dont include previous history in this snapshot
+  delete snapshot.history
+  return snapshot
+}