1 files changed, 41 insertions, 0 deletions
diff --git a/app/scripts/lib/tx-state-history-helper.js b/app/scripts/lib/tx-state-history-helper.js
new file mode 100644
index 000000000..94c7b6792
--- /dev/null
+++ b/app/scripts/lib/tx-state-history-helper.js
@@ -0,0 +1,41 @@
+const jsonDiffer = require('fast-json-patch')
+const clone = require('clone')
+
+module.exports = {
+  generateHistoryEntry,
+  replayHistory,
+  snapshotFromTxMeta,
+  migrateFromSnapshotsToDiffs,
+}
+
+
+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)
+    })
+  )
+}
+
+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
+}
+
+function replayHistory (_shortHistory) {
+  const shortHistory = clone(_shortHistory)
+  return shortHistory.reduce((val, entry) => jsonDiffer.applyPatch(val, entry).newDocument)
+}
+
+function snapshotFromTxMeta (txMeta) {
+  // create txMeta snapshot for history
+  const snapshot = clone(txMeta)
+  // dont include previous history in this snapshot
+  delete snapshot.history
+  return snapshot
+}