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 }