AppConfiguration.ts

import { config, DotenvConfigOutput, DotenvParseOutput } from "dotenv"
import { Err, Ok, Result } from "ts-results"
import Logger from "./logger"

export class AppConfiguration {
  private static instance: AppConfiguration = new AppConfiguration()
  private static requiredEnvVars: ReadonlyArray<string> = [
    "GATEWAY_NS",
    "GOOGLE_API_KEY",
    "GOOGLE_USER_EMAIL",
    "GOOGLE_SERVICE_CLIENT",
    "GOOGLE_EMAIL_PRIVATE_KEY",
    "MONGODB_URI",
  ]

  private static envs = {}

  private constructor() {
    if (AppConfiguration.instance) {
      throw new Error(
        "Error: Instantiation failed: Use AppConfiguration.getInstance() instead of new.",
      )
    }
    AppConfiguration.instance = this
  }

  public static getInstance(): AppConfiguration {
    return AppConfiguration.instance
  }

  private static confirmRequiredEnvsPresent(
    resultToCheck: DotenvConfigOutput,
  ): Result<DotenvParseOutput, Array<string>> {
    const { parsed: envs } = resultToCheck
    const errorMessages: Array<string> = []
    if (envs !== undefined) {
      this.requiredEnvVars.forEach((envVar) => {
        if (!Object.prototype.hasOwnProperty.call(envs, envVar))
          errorMessages.push(`Missing ${envVar} in .env file`)
      })
      if (errorMessages.length === 0) return Ok(envs)
    } else errorMessages.push("Apparently no envs were loaded!")
    return Err(errorMessages)
  }

  public static setEnvVars(): void {
    let result
    if (process.env.NODE_ENV === ("development" || "dev")) {
      result = config()
    } else result = process.env
    Logger.debug(
      `AppConfiguration.setEnvVars config: ${JSON.stringify(result)}`,
    )
    if (!result.error) {
      const checkEnvsResult = this.confirmRequiredEnvsPresent(result)
      if (checkEnvsResult.ok) {
        this.envs = checkEnvsResult.val
      } else {
        throw new Error(
          `Processing envs failed: ${checkEnvsResult.val}`,
        )
      }
    } else throw new Error("Problem reading environment variables")
  }

  public static getEnvVars(): Record<string, unknown> {
    return this.envs
  }
}