import type {
  ReferenceSourceEntry,
  ReferenceSourceFailureCode,
  ReferenceSourceReaderError,
} from "./ReferenceSourceReaderTypes.js";

export const failure = (
  code: ReferenceSourceReaderError["code"],
  message: string,
): ReferenceSourceReaderError => ({
  tag: "reference-source-reader",
  code,
  message,
});

export const cancelled = (): ReferenceSourceReaderError =>
  failure("cancelled", "Reference source traversal cancelled");

export const safeSize = (size: bigint): number | undefined => {
  const value = Number(size);
  return Number.isSafeInteger(value) && value >= 0 ? value : undefined;
};

const FILESYSTEM_ERROR_CODES = new Set([
  "EACCES",
  "EBADF",
  "EEXIST",
  "EIO",
  "EISDIR",
  "ELOOP",
  "EMFILE",
  // A traversed child can exceed the platform's absolute path limit even
  // though the selected root and every component are valid.
  "ENAMETOOLONG",
  "ENFILE",
  "ENOENT",
  "ENOTDIR",
  "ENOSPC",
  "EPERM",
  "EROFS",
]);

/** Preserve actionable operating-system detail while leaving invariants visible. */
export const filesystemFailureDetail = (
  cause: unknown,
  operation: string,
): string | undefined => {
  if (!(cause instanceof Error)) return undefined;
  const code: unknown = Reflect.get(cause, "code");
  if (code === "ENAMETOOLONG")
    return `${operation}: ENAMETOOLONG (entry path exceeds the operating system path limit)`;
  return typeof code === "string" && FILESYSTEM_ERROR_CODES.has(code)
    ? `${operation}: ${cause.message}`
    : undefined;
};

/** Preserve root I/O detail while separating bad selections from access failures. */
export const rootFilesystemFailure = (
  cause: unknown,
  operation: string,
):
  | {
      readonly code: "invalid-root" | "io";
      readonly message: string;
    }
  | undefined => {
  if (!(cause instanceof Error)) return undefined;
  const code: unknown = Reflect.get(cause, "code");
  if (typeof code !== "string" || !FILESYSTEM_ERROR_CODES.has(code))
    return undefined;
  return {
    code: code === "ENOENT" || code === "ENOTDIR" ? "invalid-root" : "io",
    message: `${operation}: ${cause.message}`,
  };
};

export const entryFailure = (
  ...[path, kind, code, message, size]: readonly [
    string,
    Extract<ReferenceSourceEntry, { status: "failed" }>["kind"],
    ReferenceSourceFailureCode,
    string,
    size?: number,
  ]
): ReferenceSourceEntry => ({
  status: "failed",
  kind,
  path,
  code,
  message,
  ...(size === undefined ? {} : { size }),
});