/**
 * Repository-resolution variables git reads from the environment.
 *
 * A git hook exports these into every process it runs, and they take
 * precedence over `-C`. A command scoped to a subtree then silently reads
 * whatever the hook's repository points at and reports figures for a tree
 * nobody asked about, which is worse than failing because the output looks
 * ordinary. `GIT_PREFIX` is here for the same reason: it re-anchors a relative
 * pathspec to the directory the hook was invoked from.
 */
const RESOLUTION_VARS = [
  'GIT_DIR',
  'GIT_WORK_TREE',
  'GIT_COMMON_DIR',
  'GIT_INDEX_FILE',
  'GIT_OBJECT_DIRECTORY',
  'GIT_ALTERNATE_OBJECT_DIRECTORIES',
  'GIT_NAMESPACE',
  'GIT_PREFIX',
]

/**
 * Returns the ambient environment with git's repository-resolution variables
 * removed, so `git -C <path>` resolves against `<path>` and nothing else.
 *
 * Read per call rather than captured at module load. A long-lived process can
 * have these set after import, and a snapshot would then hand git the very
 * variables this exists to strip.
 */
export function gitEnv(): Record<string, string> {
  return Object.fromEntries(
    Object.entries(process.env).filter(
      ([key, value]) => value !== undefined && !RESOLUTION_VARS.includes(key),
    ),
  ) as Record<string, string>
}