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Merge pull request #50 from ncthbrt/persistence-query
Persistence query
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,147 @@ | ||
| const { PersistedSnapshot } = require('./persistence-engine'); | ||
| const { applyOrThrowIfStopped } = require('../system-map'); | ||
| const id = x => x; | ||
|
|
||
| class PersistentQuery { | ||
| constructor (system, f, key, persistenceEngine, { snapshotKey, snapshotEvery, cacheDuration, snapshotEncoder = id, snapshotDecoder = id, encoder = id, decoder = id } = {}) { | ||
| if (!key) { | ||
| throw new Error('Persistence key required'); | ||
| } | ||
| if (typeof (key) !== 'string') { | ||
| throw new Error('Persistence key must be a string'); | ||
| } | ||
| this.persistenceEngine = persistenceEngine; | ||
|
|
||
| this.clearCache(); | ||
| this.proxy = new Proxy(() => {}, { | ||
| apply: () => { | ||
| if (!this.promise) { | ||
| this.promise = this.query(); | ||
| } else { | ||
| this.resetTimeout(); | ||
| } | ||
| return this.promise; | ||
| } | ||
| }); | ||
| this.f = f; | ||
| this.key = key; | ||
| this.snapshotKey = snapshotKey; | ||
| if (!snapshotKey) { | ||
| this.latestSnapshot = () => { this.snapshotRestored = true; return Promise.resolve(); }; | ||
| } else if (typeof (snapshotKey) !== 'string') { | ||
| throw new Error('snapshotKey must be of type string'); | ||
| } | ||
| this.snapshotDecoder = snapshotDecoder; | ||
| this.snapshotEncoder = snapshotEncoder; | ||
| this.decoder = decoder; | ||
| this.encoder = encoder; | ||
| this.promise = undefined; | ||
|
|
||
| if (!snapshotEvery) { | ||
| this.takeSnapshot = () => Promise.resolve(); | ||
| this.snapshotEvery = Number.POSITIVE_INFINITY; | ||
| } else if (typeof (snapshotEvery) !== 'number') { | ||
| throw new Error('snapshotEvery should be specified as a number. The value indicates how many messages are persisted between snapshots'); | ||
| } else if (!snapshotKey) { | ||
| throw new Error('snapshotKey must be specified in order to enable snapshotting'); | ||
| } else { | ||
| this.snapshotEvery = snapshotEvery; | ||
| this.messagesToNextSnapshot = snapshotEvery; | ||
| } | ||
| if (!cacheDuration) { | ||
| this.setTimeout = () => {}; | ||
| } else if (typeof (cacheDuration) !== 'number') { | ||
| throw new Error('cacheDuration should be specified as a number in milliseconds'); | ||
| } else { | ||
| this.cacheDuration = PersistentQuery.getSafeTimeout(cacheDuration); | ||
| this.setTimeout(); | ||
| } | ||
| } | ||
|
|
||
| clearCache () { | ||
| this.state = undefined; | ||
| this.sequenceNumber = 0; | ||
| this.messagesToNextSnapshot = undefined; | ||
| this.snapshotRestored = false; | ||
| } | ||
|
|
||
| static getSafeTimeout (timeoutDuration) { | ||
| timeoutDuration = timeoutDuration | 0; | ||
| const MAX_TIMEOUT = 2147483647; | ||
| return Math.min(MAX_TIMEOUT, timeoutDuration); | ||
| } | ||
|
|
||
| setTimeout () { | ||
| this.timeout = setTimeout(() => this.clearCache(), this.cacheDuration); | ||
| } | ||
|
|
||
| clearTimeout () { | ||
| clearTimeout(this.timeout); | ||
| } | ||
|
|
||
| resetTimeout () { | ||
| this.clearTimeout(); | ||
| this.setTimeout(); | ||
| } | ||
|
|
||
| async takeSnapshot () { | ||
| if (this.messagesToNextSnapshot <= 0) { | ||
| const snapshotState = this.snapshotEncoder(this.state); | ||
| const sequenceNumber = this.sequenceNumber; | ||
| const key = this.snapshotKey; | ||
| try { | ||
| const snapshot = new PersistedSnapshot(snapshotState, sequenceNumber, key); | ||
| await this.persistenceEngine.takeSnapshot(snapshot); | ||
| this.messagesToNextSnapshot = this.snapshotEvery; | ||
| } catch (e) { | ||
| console.error(`Failed to take snapshot ${e}`); | ||
| } | ||
| } | ||
| } | ||
|
|
||
| async latestSnapshot () { | ||
| if (!this.snapshotRestored) { | ||
| const snapshot = await this.persistenceEngine.latestSnapshot(this.snapshotKey); | ||
| if (snapshot) { | ||
| this.state = this.snapshotDecoder(snapshot.data); | ||
| this.sequenceNumber = snapshot.sequenceNumber; | ||
| } | ||
| this.messagesToNextSnapshot = this.snapshotEvery; | ||
| this.snapshotRestored = true; | ||
| } | ||
| } | ||
|
|
||
| async query () { | ||
| this.clearTimeout(); | ||
| await this.latestSnapshot(); | ||
| let result = await this.persistenceEngine | ||
| .events(this.key, this.sequenceNumber) | ||
| .reduce(async (prev, msg, index) => { | ||
| const [state, prevIndex] = await prev; | ||
| if (msg.isDeleted) { | ||
| return [state, prevIndex, msg.sequenceNumber]; | ||
| } else { | ||
| const decodedMsg = this.decoder(msg.data); | ||
| // Might not be an async function. Using promise.resolve to force it into that form | ||
| const nextState = await Promise.resolve(this.f.call(undefined, state, decodedMsg)); | ||
| return [nextState, index, msg.sequenceNumber]; | ||
| } | ||
| }, Promise.resolve([this.state, 0, this.sequenceNumber])); | ||
| const [state, messageCount, seq] = result; | ||
| this.sequenceNumber = seq; | ||
| this.messagesToNextSnapshot -= messageCount; | ||
| this.state = state; | ||
| this.takeSnapshot(); | ||
| this.promise = undefined; | ||
| this.resetTimeout(); | ||
| return state; | ||
| } | ||
| } | ||
|
|
||
| const persistentQuery = (parent, f, key, properties) => | ||
| applyOrThrowIfStopped( | ||
| parent, | ||
| parent => new PersistentQuery(parent.system, f, key, parent.system.persistenceEngine, properties).proxy | ||
| ); | ||
|
|
||
| module.exports.persistentQuery = persistentQuery; |
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