From 8ee334716e5580eb6e159b13c32202c6e37fd21a Mon Sep 17 00:00:00 2001
From: Henry Kupty <hkupty@gmail.com>
Date: Sat, 23 Mar 2024 21:35:52 +0100
Subject: [PATCH] feat: Introduce `penna.api.audit`

This should allow for better logging in exceptional cases without the
need for the proper logging infrastructure. Since the logger won't be
available during runtime, we should use this as a direct means of
notifying stdout of important events.
---
 penna-api/src/main/java/module-info.java      |  1 +
 .../src/main/java/penna/api/audit/Logger.java | 32 ++++++++++++
 .../java/penna/api/audit/PseudoLogger.java    | 22 +++++++++
 .../api/audit/internal/StdoutLogger.java      | 49 +++++++++++++++++++
 4 files changed, 104 insertions(+)
 create mode 100644 penna-api/src/main/java/penna/api/audit/Logger.java
 create mode 100644 penna-api/src/main/java/penna/api/audit/PseudoLogger.java
 create mode 100644 penna-api/src/main/java/penna/api/audit/internal/StdoutLogger.java

diff --git a/penna-api/src/main/java/module-info.java b/penna-api/src/main/java/module-info.java
index 6d4edfc0..01398327 100644
--- a/penna-api/src/main/java/module-info.java
+++ b/penna-api/src/main/java/module-info.java
@@ -13,4 +13,5 @@
 
     exports penna.api.models;
     exports penna.api.config;
+    exports penna.api.audit;
 }
\ No newline at end of file
diff --git a/penna-api/src/main/java/penna/api/audit/Logger.java b/penna-api/src/main/java/penna/api/audit/Logger.java
new file mode 100644
index 00000000..caf999ff
--- /dev/null
+++ b/penna-api/src/main/java/penna/api/audit/Logger.java
@@ -0,0 +1,32 @@
+package penna.api.audit;
+
+import penna.api.audit.internal.StdoutLogger;
+
+/**
+ * This class provides static methods for the logger to report back, specially during initialization.
+ * It is supposed to be as simple as possible and as minimally used as possible.
+ */
+public class Logger {
+    private Logger() {}
+    private static final PseudoLogger impl = new StdoutLogger();
+
+    /**
+     * Reports through the underlying logger some important event. To be used sparingly.
+     * @param level The target level.
+     * @param event The message to be printed.
+     */
+    public static void report(String level, String event) {
+        impl.report(level, event);
+    }
+
+    /**
+     * Reports an error, usually in the form of an {@link Exception}. To be used sparingly, in situations
+     * where the logger malfunctions and needs to explain upstream why it didn't work.
+     * @param level The target level.
+     * @param event The message to be printed.
+     * @param throwable The exception or error that caused the report.
+     */
+    public static void reportError(String level, String event, Throwable throwable) {
+        impl.reportError(level, event, throwable);
+    }
+}
diff --git a/penna-api/src/main/java/penna/api/audit/PseudoLogger.java b/penna-api/src/main/java/penna/api/audit/PseudoLogger.java
new file mode 100644
index 00000000..c639dc99
--- /dev/null
+++ b/penna-api/src/main/java/penna/api/audit/PseudoLogger.java
@@ -0,0 +1,22 @@
+package penna.api.audit;
+
+/**
+ * This is the internal logging mechanism, so we can still log important messages if something fails on initialization.
+ */
+public interface PseudoLogger {
+    /**
+     * This method should be used to notify an event;
+     * @param level How critical this event is;
+     * @param event The event as a short string;
+     */
+    void report(String level, String event);
+
+
+    /**
+     * This method should be used to notify a failure or an exception, handled or not;
+     * @param level How critical is the situation
+     * @param event The event as a short string;
+     * @param throwable The error that happened
+     */
+    void reportError(String level, String event, Throwable throwable);
+}
diff --git a/penna-api/src/main/java/penna/api/audit/internal/StdoutLogger.java b/penna-api/src/main/java/penna/api/audit/internal/StdoutLogger.java
new file mode 100644
index 00000000..a2b767e4
--- /dev/null
+++ b/penna-api/src/main/java/penna/api/audit/internal/StdoutLogger.java
@@ -0,0 +1,49 @@
+package penna.api.audit.internal;
+
+import penna.api.audit.PseudoLogger;
+
+/**
+ * Simple string-concat based logger just to print important messages to stdout.
+ * See {@link PseudoLogger} for more information.
+ */
+public class StdoutLogger implements PseudoLogger {
+    private final String version = StdoutLogger.class.getPackage().getImplementationVersion();
+
+    /**
+     * Builds an audit logger instance.
+     * See {@link PseudoLogger} for more information.
+     */
+    public StdoutLogger() {}
+
+    @Override
+    public void report(String level, String event) {
+        String sb = "{\"logger\":\"penna.api.audit.Logger\",\"level\":\"" +
+                level +
+                "\",\"message\":\"" +
+                event +
+                "\",\"pennaVersion\":\"" +
+                version +
+                "\"}";
+        System.out.println(sb);
+    }
+
+    @Override
+    public void reportError(String level, String event, Throwable throwable) {
+        StringBuilder sb = new StringBuilder();
+        sb.append("{\"logger\":\"penna.api.audit.Logger\",\"level\":\"");
+        sb.append(level);
+        sb.append("\",\"message\":\"");
+        sb.append(event);
+        sb.append("\",\"error\":\"");
+        sb.append(throwable.getMessage());
+        sb.append("\",\"stacktrace\":\"");
+        for (StackTraceElement stackTraceElement : throwable.getStackTrace()) {
+            sb.append(stackTraceElement.toString());
+            sb.append("\\n");
+        }
+        sb.append("\",\"pennaVersion\":\"");
+        sb.append(version);
+        sb.append("\"}");
+        System.out.println(sb);
+    }
+}