#!/usr/bin/env bash
# gstack-wtree — print a working-tree CONTENT fingerprint (a git tree hash).
#
# Builds a temp index, stages the full working tree into it (`git add -u` for
# every tracked file, then `git add -A` for the rest, so .gitignore'd scratch
# stays out and UNTRACKED source is included), and prints `git write-tree` of
# that index. An untracked `.bun/` folder at the repository root (Bun's install
# cache, which a test run can create) is left out so a passing run does not
# look like a mid-run edit (GST-421); tracked files under it still count, and a
# tree without that folder (or with it gitignored) hashes exactly as a plain
# `git add -A` would.
# Properties that make this the right staleness fingerprint, vs
# `git rev-parse HEAD^{tree}`:
#
#   - Committing identical content does NOT change the fingerprint, so a
#     record made on a dirty tree stays valid after the exact same content is
#     committed (the /ship Step 5 -> Step 16 case).
#   - Untracked new source files DO change the fingerprint, so "tests passed"
#     can't stay FRESH after a new file appears.
#   - Rebase/amend/squash that preserve content do not change it.
#
# Performance: the temp index is seeded by COPYING the real index (git writes
# it atomically via rename, so the copy is a consistent snapshot). That
# preserves the stat cache, so staging only re-hashes files whose stat
# changed — measured 40x faster than a `read-tree HEAD` seed, which zeroes
# stat data and forces a full re-hash of every tracked file. Both seeds
# produce the identical write-tree hash. Fallback: `read-tree HEAD` when the
# index copy is unavailable (fresh repo, exotic index).
#
# The real repo index is never touched. Run standalone, staged blobs land in
# the object store as unreachable objects and get gc'd like stash churn (the
# CONTENT of untracked, non-ignored files enters .git/objects until gc — the
# same property `git stash -u` has), so `git diff <tree> <tree>` between saved
# snapshots works. With GSTACK_WTREE_OBJECT_DIR set (gstack-review-log, E4),
# new objects go to that private directory instead, with the repository's
# object store as an alternate: the fingerprint works under a read-only .git
# (Codex's sandbox), and the caller owns the directory's lifetime because its
# consumers read the tree afterwards. Exit 1 outside a git repo, in a repo with
# no commits, or when a write fails (one stderr line names the cause) — callers
# treat that as "no fingerprint"; a partial hash is never printed.
set -euo pipefail

TOP=$(git rev-parse --show-toplevel 2>/dev/null) || exit 1
# Resolve the REAL index path BEFORE exporting GIT_INDEX_FILE — with the env
# var set, `git rev-parse --git-path index` returns the temp index itself and
# the stat-cache seed silently self-copies into a dead fast path.
REAL_INDEX=$(git -C "$TOP" rev-parse --git-path index 2>/dev/null || true)
# Same for the object store: the common dir's objects (linked worktrees share
# it), resolved to an absolute path before GIT_OBJECT_DIRECTORY is exported.
REAL_OBJECTS=$(git -C "$TOP" rev-parse --git-path objects 2>/dev/null || true)
OBJ_DIR="${GSTACK_WTREE_OBJECT_DIR:-}"
if [ -n "$OBJ_DIR" ] && [ ! -d "$OBJ_DIR" ]; then
  echo "gstack-wtree: private object directory $OBJ_DIR does not exist" >&2
  exit 1
fi
TMPIDX=$(mktemp "${TMPDIR:-/tmp}/gstack-wtree-XXXXXX" 2>/dev/null) || {
  echo "gstack-wtree: cannot create a temp index under ${TMPDIR:-/tmp}; set TMPDIR to a writable directory" >&2
  exit 1
}
trap 'rm -f "$TMPIDX"' EXIT
trap 'exit 130' INT TERM
export GIT_INDEX_FILE="$TMPIDX"
# Resolve relative --git-path output against the repo root. Git for Windows
# answers in drive-letter form (C:/…) wherever the path is absolute (a linked
# worktree, a submodule, --separate-git-dir); that is absolute too (#3101).
# shellcheck source=bin/gstack-path-spelling.sh
. "$(cd "$(dirname "$0")" && pwd)/gstack-path-spelling.sh"
if [ -n "$REAL_INDEX" ] && ! gstack_path_absolute "$REAL_INDEX"; then REAL_INDEX="$TOP/$REAL_INDEX"; fi
if [ -n "$REAL_OBJECTS" ] && ! gstack_path_absolute "$REAL_OBJECTS"; then REAL_OBJECTS="$TOP/$REAL_OBJECTS"; fi
if [ -n "$OBJ_DIR" ]; then
  export GIT_OBJECT_DIRECTORY="$OBJ_DIR"
  export GIT_ALTERNATE_OBJECT_DIRECTORIES="$REAL_OBJECTS${GIT_ALTERNATE_OBJECT_DIRECTORIES:+:$GIT_ALTERNATE_OBJECT_DIRECTORIES}"
fi
if [ -n "$REAL_INDEX" ] && [ -f "$REAL_INDEX" ] && cp "$REAL_INDEX" "$TMPIDX" 2>/dev/null; then
  # Carry the real index's mtime onto the copy. Git's racy-git protection
  # re-hashes any entry whose cached mtime is not older than the index file
  # itself; `cp` stamps the copy "now", which silently marks every entry
  # non-racy and lets a same-size rewrite in the same second as the original
  # `git add` keep its stale stat-cache entry — the content change vanishes
  # from the fingerprint. touch -r restores the original racy window.
  # #2687 hardening: a FAILED touch silently reopened that exact hole (the
  # copy keeps its "now" stamp). Fall through to the HEAD seed instead —
  # slower, but every entry gets re-hashed, so the fingerprint stays honest.
  if ! touch -r "$REAL_INDEX" "$TMPIDX" 2>/dev/null; then
    rm -f "$TMPIDX" 2>/dev/null || true
    git -C "$TOP" read-tree HEAD 2>/dev/null || exit 1
  fi
else
  git -C "$TOP" read-tree HEAD 2>/dev/null || exit 1
fi
# The exclude is added only when the root .bun/ exists and is not ignored: an
# exclude pathspec naming an ignored path makes `git add -A` exit 1 (GST-449),
# and an ignored .bun/ stays out of a plain `git add -A` anyway. --no-index
# asks the ignore rules alone; without it a tracked file under .bun/ makes git
# call .bun not ignored.
EXCLUDE_BUN=""
if [ -e "$TOP/.bun" ] && ! git -C "$TOP" check-ignore --no-index -q .bun 2>/dev/null; then EXCLUDE_BUN=':(exclude,top).bun'; fi
if ! ERR=$(git -C "$TOP" add -u 2>&1 >/dev/null) || ! ERR=$(git -C "$TOP" add -A -- . ${EXCLUDE_BUN:+"$EXCLUDE_BUN"} 2>&1 >/dev/null); then
  echo "gstack-wtree: cannot stage the working tree: $(printf '%s' "$ERR" | head -1)" >&2
  exit 1
fi
if ! TREE=$(git -C "$TOP" write-tree 2>&1) || ! printf '%s' "$TREE" | grep -Eqx '[0-9a-f]{40}|[0-9a-f]{64}'; then
  echo "gstack-wtree: cannot write the tree: $(printf '%s' "$TREE" | head -1)" >&2
  exit 1
fi
printf '%s\n' "$TREE"