import { readFile } from "node:fs/promises";
import path from "node:path";
import { fileURLToPath } from "node:url";
import type { PermissionRegistry } from "@ekklesia/core/authorization";
import {
  composePlatformPermissionRegistry,
  discoverModules,
  type DiscoveredModule,
} from "@ekklesia/core/modules";

export type PlatformPermissionConfigurationErrorCode = "PLATFORM_PERMISSION_CONFIGURATION_INVALID";

/** Never carries the underlying package.json path, filesystem error, module directory, manifest
 * content, or any other machine detail — a broken repository layout is a startup-time
 * configuration problem, not something to describe in detail to whatever eventually logs it. */
export class PlatformPermissionConfigurationError extends Error {
  readonly code: PlatformPermissionConfigurationErrorCode;

  constructor() {
    super("Module discovery configuration could not be resolved.");
    this.name = "PlatformPermissionConfigurationError";
    this.code = "PLATFORM_PERMISSION_CONFIGURATION_INVALID";
    this.stack = `${this.name}: ${this.message}`;
    Object.freeze(this);
  }
}

/**
 * Resolves the repository root from this compiled/source file's own location, never
 * `process.cwd()` — package-scoped test runs execute with `apps/api` as the working directory,
 * which would silently point discovery at the wrong `modules/` directory. `apps/api/dist/*.js`
 * (compiled) and `apps/api/src/*.ts` (source, under a test runner transforming TypeScript
 * on the fly) sit at the identical depth from the repository root, so the same fixed number of
 * `..` segments resolves correctly in both.
 */
function resolveRepositoryRoot(): string {
  return path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..", "..", "..");
}

interface PackageVersionFile {
  readonly version?: unknown;
}

async function readPackageVersion(packagePath: string): Promise<string> {
  let packageData: PackageVersionFile;
  try {
    packageData = JSON.parse(await readFile(packagePath, "utf8")) as PackageVersionFile;
  } catch {
    throw new PlatformPermissionConfigurationError();
  }
  if (typeof packageData.version !== "string" || packageData.version.trim().length === 0) {
    throw new PlatformPermissionConfigurationError();
  }
  return packageData.version;
}

export interface PrepareStartupModuleInventoryOptions {
  /** Test-only escape hatch: overrides the directory module discovery scans for installed
   * modules. Never set by the executable entry point — production always discovers the real
   * repository's `modules/` directory. Platform and Module SDK versions are always read from the
   * real repository's own `package.json` files regardless of this override. */
  readonly modulesDirectoryOverride?: string;
  /** Test-only escape hatch: supplies an already-discovered module list directly, skipping the
   * filesystem discovery step entirely, while still running the real `composePlatformPermissionRegistry`
   * on it — and, if startup progresses that far, driving module runtime startup with this exact
   * list too. Exists because a genuine exact permission-id collision between two modules is
   * unreachable through real discovery: module ids are unique (discovery itself rejects a
   * duplicate) and every permission id is namespaced by its own module's id, so no two
   * really-discovered modules can ever contribute the same permission id. Proving
   * `PermissionRegistryError`'s own duplicate-rejection behavior in composition, and that startup
   * has created no pool before it runs, requires supplying deliberately conflicting declarations
   * directly. (A module-vs-Core collision, by contrast, *is* reachable through real discovery — a
   * module whose own id is `"core"` — and surfaces as `ModulePermissionCompositionError`, not this
   * case; `modulesDirectoryOverride` with a real fixture is what proves that one.) Never set by the
   * executable entry point.
   */
  readonly discoveredModulesOverride?: readonly DiscoveredModule[];
}

export type ComposeStartupPermissionRegistryOptions = PrepareStartupModuleInventoryOptions;

export interface StartupModuleInventory {
  /** The exact discovered-module list — in discovery order — permission composition ran against.
   * Production startup (`apps/api/src/server.ts`) passes this same list to
   * `startDiscoveredModuleRuntime` rather than letting the module runtime rediscover modules a
   * second time. */
  readonly modules: readonly DiscoveredModule[];
  readonly permissionRegistry: PermissionRegistry;
}

/**
 * Discovers every installed module's manifest exactly once and composes the one immutable platform
 * permission registry (Core's own declarations plus every module's) from that exact discovered
 * list — the production source of truth `apps/api` enforces every request against, and the exact
 * module inventory `startDiscoveredModuleRuntime` starts from. Only manifests are read here; no
 * module server entrypoint is imported or executed, and no module lifecycle hook runs. Read the
 * platform and Module SDK versions only when this function actually executes, never at import
 * time.
 */
export async function prepareStartupModuleInventory(
  options: PrepareStartupModuleInventoryOptions = {},
): Promise<StartupModuleInventory> {
  if (options.discoveredModulesOverride) {
    const modules = options.discoveredModulesOverride;
    return Object.freeze({
      modules,
      permissionRegistry: composePlatformPermissionRegistry(modules),
    });
  }

  const repositoryRoot = resolveRepositoryRoot();
  const [platformVersion, moduleSdkVersion] = await Promise.all([
    readPackageVersion(path.join(repositoryRoot, "package.json")),
    readPackageVersion(path.join(repositoryRoot, "packages/module-sdk/package.json")),
  ]);

  const modules = await discoverModules({
    moduleSdkVersion,
    modulesDirectory: options.modulesDirectoryOverride ?? path.join(repositoryRoot, "modules"),
    platformVersion,
  });

  return Object.freeze({
    modules,
    permissionRegistry: composePlatformPermissionRegistry(modules),
  });
}

/**
 * Compatible wrapper for callers — currently only existing tests — that need this package's
 * composed registry without the discovered module list itself. (Doctor and `modules:validate` are
 * Core-owned and never call into `apps/api` at all; they call Core's own
 * `composePlatformPermissionRegistry` directly over their own already-discovered module list.)
 * Production `startApi` does not call this wrapper: it calls `prepareStartupModuleInventory`
 * directly so it can hand the exact same discovered list to `startDiscoveredModuleRuntime`, rather
 * than discarding it here and rediscovering modules a second time for runtime startup.
 */
export async function composeStartupPermissionRegistry(
  options: ComposeStartupPermissionRegistryOptions = {},
): Promise<PermissionRegistry> {
  const inventory = await prepareStartupModuleInventory(options);
  return inventory.permissionRegistry;
}