import { createSingleton, transformProperties } from "./util.ts";

export const APP_PREFIX = "crupest";
export const APP_NAME = "mailserver";

interface ConfigItemDef {
  env: string;
  description: string;
  default?: string;
}

export const CONFIG_DEFS = {
  awsAccessKeyId: { env: "AWS_USER", description: "aws access key id" },
  awsSecretAccessKey: {
    env: "AWS_PASSWORD",
    description: "aws secret access key",
  },
  awsMailBucket: {
    env: "AWS_MAIL_BUCKET",
    description: "aws s3 bucket saving raw mails",
  },
} as const satisfies Record<string, ConfigItemDef>;

type ConfigDefs = typeof CONFIG_DEFS;
type ConfigKey = keyof ConfigDefs;
type ConfigMap = {
  [K in ConfigKey]: ConfigDefs[K] & { value: string };
};

function resolveAppConfigItem(def: ConfigItemDef): string {
  const envKey =
    `${APP_PREFIX.toUpperCase()}_${APP_NAME.toUpperCase()}_${def.env}`;
  const value = Deno.env.get(envKey);
  if (value != null) return value;
  if (def.default != null) return def.default;
  throw new Error(
    `Required env ${envKey} (${def.description}) is not set.`,
  );
}

export class Config {
  private config = transformProperties(
    CONFIG_DEFS,
    (def) => ({ ...def, value: resolveAppConfigItem(def) }),
  ) as ConfigMap;

  get<K extends ConfigKey>(key: K): ConfigMap[K] {
    return this.config[key];
  }

  getValue(key: ConfigKey): string {
    return this.get(key).value;
  }
}

export const [getConfig, setConfig] = createSingleton<Config>("Config");