squid-js/src/keeper/EventHandler.ts

import { ContractEvent } from "./ContractEvent"
import ContractBase from "./contracts/ContractBase"

import { Instantiable, InstantiableConfig } from "../Instantiable.abstract"

export class EventHandler extends Instantiable {

    get count() {
        return this.events.size
    }
    private events = new Set<(blockNumber) => void>()
    private lastBlock: number
    private interval = 200
    private polling: boolean = false
    private lastTimeout: NodeJS.Timeout

    constructor(config: InstantiableConfig) {
        super()
        this.setInstanceConfig(config)
    }

    public subscribe(callback: (blockNumber: number) => void) {
        this.events.add(callback)
        this.checkBlock()

        return {
            unsubscribe: () => this.unsubscribe(callback),
        }
    }

    public unsubscribe(callback: (blockNumber: number) => void) {
        this.events.delete(callback)
        if (!this.count) {
            clearTimeout(this.lastTimeout)
            delete this.lastBlock
            this.polling = false
        }
    }

    public getEvent(contract: ContractBase, eventName: string, filter: {[key: string]: any}) {
        return new ContractEvent(this, contract, eventName, filter)
    }

    private async checkBlock(isInterval?: boolean, n = 0) {
        const blockNumber = await this.web3.eth.getBlockNumber()

        if ((this.polling && !isInterval) || !this.count) {
            return
        }
        this.polling = true

        if (!this.lastBlock) {
            this.lastBlock = blockNumber
        }

        if (this.lastBlock !== blockNumber) {
            this.events.forEach((fn) => fn(this.lastBlock + 1))
            this.lastBlock = blockNumber
        }
        this.lastTimeout = setTimeout(() => this.checkBlock(true, n++), this.interval)
    }
}