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 }