Notes2/static/js/sync.mjs

import { API } from 'api'
import { Node } from 'node'
import { h, Component, createRef } from 'preact'
import htm from 'htm'
const html = htm.bind(h)

const SYNC_COUNT = 1
const SYNC_HANDLED = 2
const SYNC_DONE = 3

export class Sync {

	constructor() {//{{{
		this.listeners = []
		this.messagesReceived = []
	}//}}}
	addListener(fn, runMessageQueue) {//{{{
		// Some handlers won't be added until a time after sync messages have been added to the queue.
		// This is an opportunity for the handler to receive the old messages in order.
		if (runMessageQueue)
			for (const msg of this.messagesReceived)
				fn(msg)
		this.listeners.push(fn)
	}//}}}
	pushMessage(msg) {//{{{
		this.messagesReceived.push(msg)
		for (const fn of this.listeners)
			fn(msg)
	}//}}}

	async run() {//{{{
		try {
			let duration = 0 // in ms

			// The latest sync node value is used to retrieve the changes
			// from the backend.
			const state = await nodeStore.getAppState('latest_sync_node')
			const oldMax = (state?.value ? state.value : 0)

			let nodeCount = await this.getNodeCount(oldMax)
			nodeCount += await nodeStore.sendQueue.count()
			const msg = { op: SYNC_COUNT, count: nodeCount }
			this.pushMessage(msg)

			await this.nodesFromServer(oldMax)
				.then(durationNodes => {
					duration = durationNodes // in ms
					console.log(`Total time: ${Math.round(1000 * durationNodes) / 1000}s`)
				})

			await this.nodesToServer()
		} finally {
			this.pushMessage({ op: SYNC_DONE, })
		}
	}//}}}
	async getNodeCount(oldMax) {//{{{
		// Retrieve the amount of values the server will send us.
		const res = await API.query('POST', `/sync/from_server/count/${oldMax}`)
		return res?.Count
	}//}}}
	async nodesFromServer(oldMax) {//{{{
		const syncStart = Date.now()
		let syncEnd
		try {
			let currMax = oldMax
			let offset = 0
			let res = { Continue: false }
			let batch = 0
			do {
				batch++
				res = await API.query('POST', `/sync/from_server/${oldMax}/${offset}`)
				if (res.Nodes.length > 0)
					console.log(`Node sync batch #${batch}`)
				offset += res.Nodes.length
				currMax = Math.max(currMax, res.MaxSeq)

				/* Go through each node and determine if they are older than
				 * the node in IndexedDB. If they are, they are just history
				 * and can be ignored since history is currently not stored
				 * in the browser.
				 *
				 * If the backed node is newer, the local node is stored in
				 * a separate table in IndexedDB to at a later stage in the
				 * sync be preserved in the backend. */

				let backendNode = null
				for (const i in res.Nodes) {
					backendNode = new Node(res.Nodes[i], -1)
					await window._sync.handleNode(backendNode)
				}

			} while (res.Continue)

			nodeStore.setAppState('latest_sync_node', currMax)
		} catch (e) {
			console.log('sync node tree', e)
		} finally {
			syncEnd = Date.now()
			const duration = (syncEnd - syncStart) / 1000
			const count = await nodeStore.nodeCount()
			console.log(`Node sync took ${duration}s`, count)
		}
		return (syncEnd - syncStart)
	}//}}}
	async handleNode(backendNode) {//{{{
		try {
			/* Retrieving the local copy of this node from IndexedDB.
			 * The backend node can be discarded if it is older than
			 * the local copy since it is considered history preserved
			 * in the backend. */
			return nodeStore.get(backendNode.UUID)
				.then(async localNode => {
					if (localNode.updated() >= backendNode.updated()) {
						console.log(`History from backend: ${backendNode.UUID}`)
						return
					}

					/* If the local node hasn't seen unsynchronized change,
					 * it can be replaced without anything else being done
					 * since it is already on the backend server.
					 *
					 * If the local node has seen change, the change is already
					 * placed into the send_queue anyway. */
					return nodeStore.add([backendNode])

				})
				.catch(async () => {
					// Not found in IndexedDB - OK to just insert since it only exists in backend.
					return nodeStore.add([backendNode])
				})
		} catch (e) {
			console.error(e)
		} finally {
			this.pushMessage({ op: SYNC_HANDLED, count: 1 })
		}
	}//}}}
	async nodesToServer() {//{{{
		const BATCH_SIZE = 32
		while (true) {
			try {
				// Send nodes in batches until everything is sent, or an error has occured.
				const nodesToSend = await nodeStore.sendQueue.retrieve(BATCH_SIZE)
				if (nodesToSend.length === 0)
					break
				console.debug(`Sending ${nodesToSend.length} node(s) to server`)

				const request = {
					NodeData: JSON.stringify(nodesToSend),
				}
				const res = await API.query('POST', '/sync/to_server', request)
				if (!res.OK) {
					// TODO - implement better error management here.
					console.log(res)
					alert(res)
					return
				}

				// Nodes are archived on server and can now be deleted from the send queue.
				const keys = nodesToSend.map(node => node.ClientSequence)
				console.log(await nodeStore.sendQueue.delete(keys))
				this.pushMessage({ op: SYNC_HANDLED, count: nodesToSend.length })

			} catch (e) {
				console.trace(e)
				alert(e)
				return
			}
		}
	}//}}}
}

export class SyncProgress extends Component {
	constructor() {//{{{
		super()
		this.state = {
			nodesToSync: 0,
			nodesSynced: 0,
			syncedDone: false,
		}
	}//}}}
	componentDidMount() {//{{{
		window._sync.addListener(msg => this.progressHandler(msg), true)
	}//}}}
	getSnapshotBeforeUpdate(_, prevState) {//{{{
		if (!prevState.syncedDone && this.state.syncedDone)
			setTimeout(() => document.getElementById('sync-progress')?.classList.add('hidden'), 750)
	}//}}}
	progressHandler(msg) {//{{{
		switch (msg.op) {
			case SYNC_COUNT:
				this.setState({ nodesToSync: msg.count })
				break

			case SYNC_HANDLED:
				this.setState({ nodesSynced: this.state.nodesSynced + msg.count })
				break


			case SYNC_DONE:
				this.setState({ syncedDone: true })
				break
		}
	}//}}}
	render(_, { nodesToSync, nodesSynced }) {//{{{
		if (nodesToSync === 0)
			return html`<div id="sync-progress"></div>`

		return html`
			<div id="sync-progress">
				<progress min=0 max=${nodesToSync} value=${nodesSynced}></progress>
				<div class="count">${nodesSynced} / ${nodesToSync}</div>
			</div>
		`
	}//}}}
}