From f9f8c4cceb087549fca1a786de403f555d14b09b Mon Sep 17 00:00:00 2001
From: Josh Hawkins <32435876+hawkeye217@users.noreply.github.com>
Date: Thu, 18 Sep 2025 07:51:03 -0500
Subject: [PATCH] implement replacement rules for cleaning up and normalizing
 plates

---
 frigate/config/classification.py              | 11 ++++++++++
 .../common/license_plate/mixin.py             | 21 +++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/frigate/config/classification.py b/frigate/config/classification.py
index 63e89421c..98e0db046 100644
--- a/frigate/config/classification.py
+++ b/frigate/config/classification.py
@@ -217,6 +217,13 @@ class CameraFaceRecognitionConfig(FrigateBaseModel):
     model_config = ConfigDict(extra="forbid", protected_namespaces=())
 
 
+class ReplaceRule(FrigateBaseModel):
+    pattern: str = Field(..., title="Regex pattern to match.")
+    replacement: str = Field(
+        ..., title="Replacement string (supports backrefs like '\\1')."
+    )
+
+
 class LicensePlateRecognitionConfig(FrigateBaseModel):
     enabled: bool = Field(default=False, title="Enable license plate recognition.")
     model_size: str = Field(
@@ -269,6 +276,10 @@ class LicensePlateRecognitionConfig(FrigateBaseModel):
         title="The device key to use for LPR.",
         description="This is an override, to target a specific device. See https://onnxruntime.ai/docs/execution-providers/ for more information",
     )
+    replace_rules: List[ReplaceRule] = Field(
+        default_factory=list,
+        title="List of regex replacement rules for normalizing detected plates. Each rule has 'pattern' and 'replacement'.",
+    )
 
 
 class CameraLicensePlateRecognitionConfig(FrigateBaseModel):
diff --git a/frigate/data_processing/common/license_plate/mixin.py b/frigate/data_processing/common/license_plate/mixin.py
index 83019efc3..d2083afec 100644
--- a/frigate/data_processing/common/license_plate/mixin.py
+++ b/frigate/data_processing/common/license_plate/mixin.py
@@ -360,6 +360,27 @@ class LicensePlateProcessingMixin:
                 conf for conf_list in qualifying_confidences for conf in conf_list
             ]
 
+            # Apply replace rules to combined_plate if configured
+            original_combined = combined_plate
+            if self.lpr_config.replace_rules:
+                for rule in self.lpr_config.replace_rules:
+                    try:
+                        pattern = getattr(rule, "pattern", "")
+                        replacement = getattr(rule, "replacement", "")
+                        if pattern:
+                            combined_plate = re.sub(
+                                pattern, replacement, combined_plate
+                            )
+                    except re.error as e:
+                        logger.warning(
+                            f"{camera}: Invalid regex in replace_rules '{pattern}': {e}"
+                        )
+
+            if combined_plate != original_combined:
+                logger.debug(
+                    f"{camera}: Rules applied: '{original_combined}' -> '{combined_plate}'"
+                )
+
             # Compute the combined area for qualifying boxes
             qualifying_boxes = [boxes[i] for i in qualifying_indices]
             qualifying_plate_images = [