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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
op (the operation performed),
path (the key and if a nested object then each key will be seperated with a `/`)
value
with the first entry having the note and a timestamp when the change took place
@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
@returns {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 (entry[0]) {
if (note) entry[0].note = note
entry[0].timestamp = Date.now()
}
return entry
}
/**
Recovers previous txMeta state obj
@returns {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
}
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