feat: add safe_render using Jinja2; add tests

app/templates.py

@@ -0,0 +1,43 @@
+import re
+from typing import Any, Dict
+
+import jinja2
+
+# Create a minimal Jinja2 environment for text templates.
+# Use StrictUndefined so missing variables raise exceptions during rendering.
+ENV = jinja2.Environment(
+    undefined=jinja2.StrictUndefined,
+    autoescape=False,
+)
+
+
+def _convert_braced_format_to_jinja(template: str) -> str:
+    """
+    Convert simple `{var}` style placeholders into Jinja `{{ var }}` so legacy templates keep working.
+    This will not touch existing `{{ }}` or `{% %}`.
+    """
+    # Skip conversion if template already contains jinja markers
+    if ("{{" in template) or ("{%" in template):
+        return template
+
+    # Replace single-brace simple identifiers like {a_b} or {a.b} -> {{ a_b }} or {{ a.b }}
+    pattern = re.compile(r'(?<!\{)\{([A-Za-z0-9_\.]+)\}(?!\})')
+    return pattern.sub(r'{{ \1 }}', template)
+
+
+def safe_render(template_str: str, context: Dict[str, Any]) -> str:
+    """
+    Safely render a template string using Jinja2 with StrictUndefined.
+    - Accepts legacy `{var}` placeholders by converting them to Jinja style.
+    - Raises jinja2 exceptions when rendering fails.
+    """
+    if template_str is None:
+        raise ValueError("template_str is None")
+
+    tpl = _convert_braced_format_to_jinja(template_str)
+    jtpl = ENV.from_string(tpl)
+    # Jinja expects normal Python types in context; if context contains Pydantic models,
+    # they should be converted by caller to plain dicts.
+    return jtpl.render(**context)
+
+

tests/test_templates.py

@@ -0,0 +1,19 @@
+import pytest
+
+from app.templates import safe_render
+
+
+def test_safe_render_legacy_and_nested():
+    tpl = "收到{actual_ref_amt}元 by {trans_order_info.remark}"
+    ctx = {"actual_ref_amt": 88.88, "trans_order_info": {"remark": "order123"}}
+    out = safe_render(tpl, ctx)
+    assert "88.88" in out
+    assert "order123" in out
+
+
+def test_safe_render_missing_var_raises():
+    tpl = "Hello {missing_var}"
+    with pytest.raises(Exception):
+        safe_render(tpl, {})
+
+