simpleFileState.ts

import {ObjectStoreInjectable} from "./objectStore.injectable";
import {Container} from "aurelia-dependency-injection";
import {HeadObjectOutput} from "aws-sdk/clients/s3";

export class SimpleFileState<T> {
    private _assetId: string;
    private _store: ObjectStoreInjectable;
    public state: FileState<T>;
    private _inFlight: boolean = false;

    constructor(private _container: Container) {
    }

    public configure(assetId: string): SimpleFileState<T> {
        this._assetId = assetId;
        return this;
    }

    public async init() {
        console.log('SimpleFileState::init');
        this._store = this._container.get(ObjectStoreInjectable);
        await this._touch();
    }

    private async _touch(): Promise<void> {
        console.log('SimpleFileState::touch');
        const existingState: HeadObjectOutput = await this._store.hasKey(this._assetId);
        if (existingState) {
            console.log('SimpleFileState::touch::assetId', this._assetId);
            this.state = await this._store.getObjectByJsonKey(this._assetId);
            console.log('Initial file state set to: ', this.state);
        } else {
            this.state = { entities: [] };
            await this._store.putObject(JSON.stringify(this.state), this._assetId, {}, 'application/json');
            console.log('New initial file state created!');
        }
    }

    private async ensureAtomic(handle: () => Promise<void>) {
        if (this._inFlight) {
            throw new Error("race condition encountered");
        } else {
            this._inFlight = true;
            await handle()
            this._inFlight = false;
        }
    }

    public async persist(): Promise<void> {
       await this.ensureAtomic(async () => {
           const str: string = JSON.stringify(this.state);
           const type: string = 'application/json';
           const response: string = await this._store.putObject(str, this._assetId, {}, type);
           console.log('Object Store updated on: persist()', response);
       });
    }
}

export interface FileState<T> { entities: T[];  }