Deduplicate campaign template rendering

src/govoplan_campaign/backend/template_rendering.py

@@ -0,0 +1,55 @@
+from __future__ import annotations
+
+import re
+from collections.abc import Mapping
+from typing import Any
+
+
+_DOLLAR_FIELD_PATTERN = re.compile(r"(?<!\\)\$\{(.*?)(?<!\\)\}")
+_BRACE_FIELD_PATTERN = re.compile(r"(?<!\\)\{\{\s*(.*?)\s*\}\}")
+
+
+def normalize_template_key(raw: str) -> str:
+    key = raw.strip()
+    if key.startswith("fields."):
+        key = key.removeprefix("fields.")
+    elif key.startswith("local."):
+        key = "local::" + key.removeprefix("local.")
+    elif key.startswith("global."):
+        key = "global::" + key.removeprefix("global.")
+
+    if key.startswith("local::") or key.startswith("global::"):
+        return key
+    if key.startswith("local:"):
+        return "local::" + key.removeprefix("local:")
+    if key.startswith("global:"):
+        return "global::" + key.removeprefix("global:")
+    return key
+
+
+def render_template(
+    template: str,
+    values: Mapping[str, Any],
+    *,
+    keep_missing: bool = True,
+) -> str:
+    def replace(match: re.Match[str]) -> str:
+        key = normalize_template_key(match.group(1))
+        if key in values:
+            value = values[key]
+            return "" if value is None else str(value)
+        return match.group(0) if keep_missing else ""
+
+    rendered = _DOLLAR_FIELD_PATTERN.sub(replace, template)
+    rendered = _BRACE_FIELD_PATTERN.sub(replace, rendered)
+    return rendered.replace(r"\${", "${").replace(r"\}", "}")
+
+
+def find_unresolved_placeholders(text: str | None) -> set[str]:
+    if not text:
+        return set()
+    return {
+        normalize_template_key(match.group(1))
+        for pattern in (_DOLLAR_FIELD_PATTERN, _BRACE_FIELD_PATTERN)
+        for match in pattern.finditer(text)
+    }