#!/usr/bin/env bash
# 组合指针不倒退：HEAD 中每个 gitlink（deps/*、modules/*）相对 origin/main
# 只能前进——新 pin 必须以 origin/main 的旧 pin 为祖先。事故原型：PR #682
# 合入了过期分支，其树把五个组件 pin 重置回批次前的值，静默丢掉了 main 上
# batch-1 的组合。
#
# ┌─ 逃生口（须 owner Review）──────────────────────────────────────────────┐
# │ PIN_REGRESSION_SKIP=1  声明这是一次有意的降级：失败改为醒目的 warn 并   │
# │                        退出 0。只用于经组件 owner 审阅的刻意回退，PR   │
# │                        描述须写明原因；不得用来绕过过期分支。         │
# └─────────────────────────────────────────────────────────────────────────┘
#
# 其他开关：
#   PIN_REGRESSION_NO_FETCH=1  旧 pin 在子仓本地缺失时不尝试 fetch（测试/离线用）。
#
# 在当前工作目录所属仓库的顶层运行。origin/main 本地不可解析（浅检出）时只告警、退出 0。
set -euo pipefail
root=$(git rev-parse --show-toplevel)
cd "$root"

base=origin/main
skip=${PIN_REGRESSION_SKIP:-0}

if ! git rev-parse --verify -q "$base^{commit}" >/dev/null; then
  echo "warn: $base is not resolvable locally; pin regression check skipped" >&2
  exit 0
fi

fail=0

declare -A main_pins=()
while read -r mode _typ sha path; do
  [ "$mode" = "160000" ] || continue
  main_pins["$path"]=$sha
done < <(git ls-tree -r "$base")

# 子仓须是独立检出的仓库；未初始化时 git -C 会落到 Dev 自身。
own_repo() {
  local path="$1" top
  top=$(git -C "$path" rev-parse --show-toplevel 2>/dev/null) || return 1
  [ "$top" = "$root/$path" ]
}

has_commit() {
  git -C "$1" cat-file -e "$2^{commit}" 2>/dev/null
}

ensure_commit() {
  local path="$1" sha="$2"
  has_commit "$path" "$sha" && return 0
  [ "${PIN_REGRESSION_NO_FETCH:-0}" = "1" ] && return 1
  git -C "$path" fetch -q origin "$sha" >/dev/null 2>&1 || true
  has_commit "$path" "$sha"
}

regress() {
  if [ "$skip" = "1" ]; then
    echo "warn: PIN_REGRESSION_SKIP=1 — $* (deliberate downgrade; requires owner review)" >&2
  else
    echo "pin: $*" >&2
    fail=1
  fi
}

while read -r mode _typ new path; do
  [ "$mode" = "160000" ] || continue
  old=${main_pins["$path"]:-}
  if [ -z "$old" ]; then
    echo "ok $path (new, not on $base)"
    continue
  fi
  if [ "$old" = "$new" ]; then
    echo "ok $path"
    continue
  fi
  if ! own_repo "$path"; then
    regress "$path is not checked out; cannot verify ${new:0:12} descends from $base ${old:0:12}"
    continue
  fi
  if ! ensure_commit "$path" "$old"; then
    regress "$path $base pin $old is missing locally and could not be fetched; cannot verify no regression"
    continue
  fi
  if ! ensure_commit "$path" "$new"; then
    regress "$path HEAD pin $new is missing locally and could not be fetched; cannot verify no regression"
    continue
  fi
  if git -C "$path" merge-base --is-ancestor "$old" "$new"; then
    echo "ok $path (forward ${old:0:12}..${new:0:12})"
    continue
  fi
  regress "$path moves BACKWARD: $base is ${old:0:12}, HEAD is ${new:0:12} (not a descendant)." \
"This is the PR #682 pattern (a stale branch resetting pins over main): merge $base and re-pin," \
"or set PIN_REGRESSION_SKIP=1 for an owner-reviewed deliberate downgrade"
done < <(git ls-tree -r HEAD)

if [ "$fail" -ne 0 ]; then
  exit 1
fi
echo "pin regression ok"