import path from "node:path";
import {
  isUsableModulesDirectoryPath,
  MODULES_DIRECTORY_INVALID_MESSAGE,
  ModuleDiscoveryError,
} from "./discovery.js";

/** The host environment variable that selects the installed-modules directory (ADR 0048). */
export const MODULES_DIRECTORY_ENVIRONMENT_VARIABLE = "EKKLESIA_MODULES_DIR";

export interface ResolveModulesDirectoryOptions {
  /** The raw configured value, exactly as the host environment supplied it; `undefined` when the
   * variable is unset. */
  readonly configured: string | undefined;
  /** Where the platform itself is installed. Only consulted for the development default. */
  readonly repositoryRoot: string;
}

/** Spreads directly into `ModuleDiscoveryOptions`, so every consumer discovers through the same
 * selection, including whether a missing directory is an error. */
export interface ModulesDirectorySelection {
  readonly modulesDirectory: string;
  readonly modulesDirectoryRequired: boolean;
}

/**
 * The one place an installation's modules directory is chosen (ADR 0048).
 *
 * - Unset: `<repositoryRoot>/modules`, the development checkout's own directory. A checkout without
 *   one has no modules, exactly as before.
 * - Set: an absolute path, normalized and used as given — never resolved against the repository or
 *   the working directory — and required to exist when discovery reads it. The shipping image sets
 *   it to `/var/lib/ekklesia/modules`.
 *
 * Anything else throws a `ModuleDiscoveryError` carrying `MODULES_DIRECTORY_INVALID` and a fixed
 * message, so every executable already reports it through the discovery error path it has, and the
 * supplied value never reaches an error, a log, or a report.
 *
 * Nothing here — and nothing that calls it — locates the platform's own files relative to the
 * result: Core's migrations and package metadata live under `repositoryRoot`, wherever modules are.
 */
export function resolveModulesDirectory(
  options: ResolveModulesDirectoryOptions,
): ModulesDirectorySelection {
  if (options.configured === undefined) {
    return Object.freeze({
      modulesDirectory: path.join(options.repositoryRoot, "modules"),
      modulesDirectoryRequired: false,
    });
  }
  if (!isUsableModulesDirectoryPath(options.configured)) {
    throw new ModuleDiscoveryError([
      {
        code: "MODULES_DIRECTORY_INVALID",
        message: MODULES_DIRECTORY_INVALID_MESSAGE,
        moduleDirectory: ".",
      },
    ]);
  }
  const normalized = path.normalize(options.configured);
  return Object.freeze({
    modulesDirectory:
      normalized.length > 1 && normalized.endsWith(path.sep) ? normalized.slice(0, -1) : normalized,
    modulesDirectoryRequired: true,
  });
}