Merge pull request #9 from GSS-Cogs/#4-implement-logger

Author: SarahJohnsonONS

.gitignore

@@ -1 +1,5 @@
-.coverage
+.coverage
+.venv
+.DS_Store
+*.pyc
+.vscode

dpytools/logger/logger.py

@@ -1,2 +1,157 @@
+from typing import Dict, List, Optional, Union
+import structlog
+import traceback
+import json
+from datetime import datetime, timezone
 
-logger = "I will be the logger"
+
+def level_to_severity(level: int) -> int:
+    """
+    Helper to convert logging level to severity, please
+    see: https://github.com/ONSdigital/dp-standards/blob/main/LOGGING_STANDARDS.md#severity-levels
+    """
+    if level > 40:
+        return 0
+    elif level > 30:
+        return 1
+    elif level > 20:
+        return 2
+    else:
+        return 3
+
+
+def create_error_dict(error: Exception) -> List[Dict]:
+    """
+    Take a python Exception and create a sub dict/document
+    matching DP logging standards.
+    """
+
+    # Note: "stack trace" guidance is very go orientated,
+    # this will be fine for now.
+    error_dict = {
+        "message": str(error),
+        "stack_trace": traceback.format_exc().split("\n"),
+    }
+
+    # Listify in keeping with expected DP logging structures
+    return [error_dict]
+
+
+def dp_serializer(event_log, **kw) -> Dict:
+    """
+    Simple serialiser to align structlog defaults
+    with output expected by:
+    https://github.com/ONSdigital/dp-standards/blob/main/LOGGING_STANDARDS.md
+    """
+
+    # Note: literally just avoiding also logging the superfluous top level
+    # "event" key - we just want its contents
+    return json.dumps(event_log["event"], **kw)
+
+
+class DpLogger:
+    def __init__(self, namespace: str, test_mode: bool = False):
+        """
+        Simple python logger to create structured logs in keeping
+        with https://github.com/ONSdigital/dp-standards/blob/main/LOGGING_STANDARDS.md
+
+        namespace: (required) the namespace for the app in question
+        test_mode: FOR USAGE DURING TESTING ONLY, makes logging statements return their structured logs.
+        """
+        structlog.configure(
+            processors=[structlog.processors.JSONRenderer(dp_serializer)]
+        )
+        self._logger = structlog.stdlib.get_logger()
+        self.namespace = namespace
+        self.test_mode = test_mode
+
+    def _log(
+        self,
+        event,
+        level,
+        error: Optional[List] = None,
+        data: Optional[Dict] = None,
+        raw: str = None,
+    ):
+        log_entry = self._create_log_entry(event, level, data, error, raw)
+        self._logger.log(level, log_entry)
+
+        if self.test_mode:
+            return log_entry
+
+    def _create_log_entry(self, event, level, data, error, raw) -> Dict:
+        log_entry = {
+            "created_at": datetime.now(timezone.utc).isoformat(),
+            "namespace": self.namespace,
+            "event": event,
+            "trace_id": "not-implemented",
+            "span_id": "not-implemented",
+            "severity": level_to_severity(level),
+            "data": data if data is not None else {},
+        }
+
+        if error:
+            log_entry["errors"] = create_error_dict(error)
+
+        if raw:
+            log_entry["raw"] = raw
+
+        return log_entry
+
+    def debug(self, event: str, raw: str = None, data: Dict = None):
+        """
+        Log at the debug level.
+
+        event: the thing that's happened, a simple short english statement
+        raw  : a raw string of any log messages captured for a third party library
+        data : arbitrary key-value pairs that may be of use in providing context
+        """
+        self._log(event, 10, raw=raw, data=data)
+
+    def info(self, event: str, raw: str = None, data: Dict = None):
+        """
+        Log at the info level.
+
+        event: the thing that's happened, a simple short english statement
+        raw  : a raw string of any log messages captured for a third party library
+        data : arbitrary key-value pairs that may be of use in providing context
+        """
+        self._log(event, 20, raw=raw, data=data)
+
+    def warning(self, event: str, raw: str = None, data: Dict = None):
+        """
+        Log at the warning level.
+
+        event: the thing that's happened, a simple short english statement
+        raw  : a raw string of any log messages captured for a third party library
+        data : arbitrary key-value pairs that may be of use in providing context
+        """
+        self._log(event, 30, raw=raw, data=data)
+
+    def error(self, event: str, error: Exception, raw: str = None, data: Dict = None):
+        """
+        Log at the error level.
+
+        event: the thing that's happened, a simple short english statement
+        error: a caught python Exceotion
+        raw  : a raw string of any log messages captured for a third party library
+        data : arbitrary key-value pairs that may be of use in providing context
+        """
+        self._log(event, 40, error=error, raw=raw, data=data)
+
+    def critical(
+        self, event: str, error: Exception, raw: str = None, data: Dict = None
+    ):
+        """
+        IMPORTANT: You should only be logging at the critical level during
+        application failure, i.e if you're app is not in this process of falling
+        over you should not be logging a critical.
+
+        Log at the critical level.
+
+        event: the thing that's happened, a simple short english statement
+        error: a caught python Exceotion
+        raw  : a raw string of any log messages captured for a third party library
+        data : arbitrary key-value pairs that may be of use in providing context
+        """
+        self._log(event, 50, error=error, raw=raw, data=data)