import { loadConfig } from "@smithy/node-config-provider";
import { Endpoint } from "@smithy/types";
import { parseUrl } from "@smithy/url-parser";

import { Endpoint as InstanceMetadataEndpoint } from "../config/Endpoint";
import { CONFIG_ENDPOINT_NAME, ENDPOINT_CONFIG_OPTIONS, ENV_ENDPOINT_NAME } from "../config/EndpointConfigOptions";
import { EndpointMode } from "../config/EndpointMode";
import {
  CONFIG_ENDPOINT_MODE_NAME,
  ENDPOINT_MODE_CONFIG_OPTIONS,
  ENV_ENDPOINT_MODE_NAME,
} from "../config/EndpointModeConfigOptions";

/**
 * Returns the host to use for instance metadata service call.
 *
 * The host is read from endpoint which can be set either in
 * {@link ENV_ENDPOINT_NAME} environment variable or {@link CONFIG_ENDPOINT_NAME}
 * configuration property.
 *
 * If endpoint is not set, then endpoint mode is read either from
 * {@link ENV_ENDPOINT_MODE_NAME} environment variable or {@link CONFIG_ENDPOINT_MODE_NAME}
 * configuration property. If endpoint mode is not set, then default endpoint mode
 * {@link EndpointMode.IPv4} is used.
 *
 * If endpoint mode is set to {@link EndpointMode.IPv4}, then the host is {@link Endpoint.IPv4}.
 * If endpoint mode is set to {@link EndpointMode.IPv6}, then the host is {@link Endpoint.IPv6}.
 *
 * @returns Host to use for instance metadata service call.
 *
 * @internal
 */
export const getInstanceMetadataEndpoint = async (): Promise<Endpoint> =>
  parseUrl((await getFromEndpointConfig()) || (await getFromEndpointModeConfig()));

const getFromEndpointConfig = async (): Promise<string | undefined> => loadConfig(ENDPOINT_CONFIG_OPTIONS)();

const getFromEndpointModeConfig = async (): Promise<string> => {
  const endpointMode = await loadConfig(ENDPOINT_MODE_CONFIG_OPTIONS)();
  switch (endpointMode) {
    case EndpointMode.IPv4:
      return InstanceMetadataEndpoint.IPv4;
    case EndpointMode.IPv6:
      return InstanceMetadataEndpoint.IPv6;
    default:
      throw new Error(`Unsupported endpoint mode: ${endpointMode}.` + ` Select from ${Object.values(EndpointMode)}`);
  }
};