import { API } from 'api'
import { Node } from 'node'
import { CustomHTMLElement } from './lib/custom_html_element.mjs'

export class Sync {
	constructor() {//{{{
		this.listeners = []
		this.messagesReceived = []
	}//}}}

	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()

			_mbus.dispatch('SYNC_COUNT', { count: nodeCount })

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

			await this.nodesToServer()
		} finally {
			_mbus.dispatch('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/${oldMax}`)
		return res?.Count
	}//}}}
	async nodesFromServer(oldMax) {//{{{
		const syncStart = Date.now()
		let syncEnd
		let handled = 0
		try {
			let currMax = oldMax
			let offset = 0
			let res = { Continue: false }
			let batch = 0
			do {
				batch++
				res = await API.query('POST', `/sync/from_server/${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

				// Create a single transaction to be used in the chain of
				// this sync. Otherwise it would take more time to create
				// transactions for each node.
				const trx = nodeStore.newTransaction('nodes', 'readwrite')
				const objstore = trx.objectStore('nodes')

				for (const i in res.Nodes) {
					backendNode = new Node(res.Nodes[i], -1)
					await this.handleNode(backendNode, objstore)

					handled++
					if (handled % 100 === 0)
						_mbus.dispatch('SYNC_HANDLED', { handled })
				}

			} while (res.Continue)
			_mbus.dispatch('SYNC_HANDLED', { handled })

			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, objstore) {//{{{
		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, objstore)
				.then(localNode => {
					if (localNode.updated() >= backendNode.updated()) {
						console.debug(`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], objstore)

				})
				.catch(() => {
					// Not found in IndexedDB - OK to just insert since it only exists in backend.
					return nodeStore.add([backendNode], objstore)
				})
		} catch (e) {
			console.error(e)
		} finally {
			//_mbus.dispatch('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.error(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)
				await nodeStore.sendQueue.delete(keys)
				_mbus.dispatch('SYNC_UPLOADED', { count: nodesToSend.length })

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

export class N2SyncProgress extends CustomHTMLElement {
	static {
		this.tmpl = document.createElement('template')
		this.tmpl.innerHTML = `
			<progress data-el="progress" min=0 max=137 value=0></progress>
			<div data-el="count" class="count">0 / 0</div>
		`
	}
	constructor() {//{{{
		super()

		this.reset()
		_mbus.subscribe('SYNC_COUNT', event => this.progressHandler(event))
		_mbus.subscribe('SYNC_HANDLED', event => this.progressHandler(event))
		_mbus.subscribe('SYNC_DONE', event => this.progressHandler(event))
	}//}}}
	reset() {//{{{
		this.state = {
			nodesToSync: 0,
			nodesSynced: 0,
		}
	}//}}}
	progressHandler(event) {//{{{
		const eventData = event.detail.data
		switch (event.type) {
			case 'SYNC_COUNT':
				this.state.nodesToSync = eventData.count
				this.setSyncState(true)
				break

			case 'SYNC_HANDLED':
				this.state.nodesSynced = eventData.handled
				break

			case 'SYNC_DONE':
				// Hides the progress bar.
				this.setSyncState(false)

				// Don't update anything if nothing was synced.
				if (this.state.nodesSynced === 0)
					break

				// Reload the tree nodes to reflect the new/updated nodes.
				window._app.tree.reset()
				break
		}
		this.render()
	}//}}}
	render() {//{{{
		this.elProgress.max = this.state.nodesToSync
		this.elProgress.value = this.state.nodesSynced
		this.elCount.innerText = `${this.state.nodesSynced} / ${this.state.nodesToSync}`
	}//}}}
	setSyncState(state) {// {{{
		if (state)
			this.classList.add('show')
		else
			setTimeout(() => this.classList.remove('show'), 1500)
	}// }}}
}
customElements.define('n2-syncprogress', N2SyncProgress)

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