name: Check cpp / md pair

on:
  push:
    paths:
      - '*.cpp'
      - '*.md'

permissions:
  contents: read

jobs:
  check-md-header:
    name: Check markdown header
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Validate md first line
        run: |
          set -euo pipefail

          BEFORE="${{ github.event.before }}"
          AFTER="${{ github.event.after }}"

          # 处理新分支第一次 push 的情况（before 为全零）
          if [ "$BEFORE" = "0000000000000000000000000000000000000000" ]; then
            CHANGED_FILES=$(git diff --name-only --diff-filter=ACM 4b825dc642cb6eb9a060e54bf8d69288fbee4904 "$AFTER" || true)
          else
            CHANGED_FILES=$(git diff --name-only --diff-filter=ACM "$BEFORE" "$AFTER" || true)
          fi

          # 筛选出根目录下的 .cpp 文件
          CPP_FILES=$(echo "$CHANGED_FILES" | grep -E '^[^/]+\.cpp$' || true)

          if [ -z "$CPP_FILES" ]; then
            echo "本次 push 没有根目录下的 .cpp 文件变更，跳过检查。"
            exit 0
          fi

          EXIT_CODE=0

          while IFS= read -r cpp_file; do
            [ -z "$cpp_file" ] && continue
            base=$(basename "$cpp_file" .cpp)
            md_file="${base}.md"

            if [ ! -f "$md_file" ]; then
              echo "::error file=${cpp_file}::对应的 Markdown 文件 ${md_file} 不存在"
              EXIT_CODE=1
              continue
            fi

            FIRST_LINE=$(head -n 1 "$md_file")

            # 检查第一行是否匹配 "# <base> 任意内容"
            if ! grep -qE "^# ${base} .*$" <<< "$FIRST_LINE"; then
              echo "::error file=${md_file},line=1::Markdown 第一行格式错误。期望以 '# ${base} ' 开头，实际为: ${FIRST_LINE}"
              EXIT_CODE=1
            else
              echo "✅ ${md_file} 第一行格式正确: ${FIRST_LINE}"
            fi
          done <<< "$CPP_FILES"

          exit $EXIT_CODE