Add an events TrimCommand

Events can be trimmed by size, or to a specific event.  The size option
is useful for cron jobs.

Change-Id: I7eea3b3ecb417012413d79c49df61463fbfaaca2

src/main/java/com/googlesource/gerrit/plugins/events/SshModule.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/events/SshModule.java b/src/main/java/com/googlesource/gerrit/plugins/events/SshModule.java
index 7eb00c9..ee7f167 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/events/SshModule.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/events/SshModule.java
@@ -20,5 +20,6 @@
   @Override
   protected void configureCommands() {
     command(StreamEvents.class);
+    command(TrimCommand.class);
   }
 }

src/main/java/com/googlesource/gerrit/plugins/events/TrimCommand.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/events/TrimCommand.java b/src/main/java/com/googlesource/gerrit/plugins/events/TrimCommand.java
new file mode 100644
index 0000000..ecf5a16
--- /dev/null
+++ b/src/main/java/com/googlesource/gerrit/plugins/events/TrimCommand.java
@@ -0,0 +1,55 @@
+// Copyright (C) 2016 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.googlesource.gerrit.plugins.events;
+
+import com.google.gerrit.common.data.GlobalCapability;
+import com.google.gerrit.extensions.annotations.RequiresCapability;
+import com.google.gerrit.sshd.CommandMetaData;
+import com.google.gerrit.sshd.SshCommand;
+import com.google.inject.Inject;
+import org.kohsuke.args4j.Option;
+
+@RequiresCapability(GlobalCapability.ADMINISTRATE_SERVER)
+@CommandMetaData(
+  name = "trim",
+  descr = "Trim old events up to and including trim-id from EventStore"
+)
+final class TrimCommand extends SshCommand {
+  @Option(
+    name = "--trim-id",
+    metaVar = "TRIM_ID",
+    usage = "Trim old events up to and including trim-id from EventStore"
+  )
+  protected long trim = -1;
+
+  @Option(name = "--size", metaVar = "SIZE", usage = "Trim and keep SIZE events")
+  protected long size = -1;
+
+  protected final EventStore store;
+
+  @Inject
+  TrimCommand(EventStore store) {
+    this.store = store;
+  }
+
+  public void run() throws Exception {
+    if (trim != -1) {
+      store.trim(trim);
+    }
+    if (size != -1) {
+      store.trim(store.getHead() - size);
+    }
+  }
+}

src/main/resources/Documentation/cmd-trim.md

diff --git a/src/main/resources/Documentation/cmd-trim.md b/src/main/resources/Documentation/cmd-trim.md
new file mode 100644
index 0000000..35ab609
--- /dev/null
+++ b/src/main/resources/Documentation/cmd-trim.md
@@ -0,0 +1,41 @@
+@PLUGIN@ trim
+=============
+
+NAME
+----
+@PLUGIN@ trim - Trim old events up from EventStore
+
+SYNOPSIS
+--------
+```
+ssh -p @SSH_PORT@ @SSH_HOST@ @PLUGIN@ trim
+   [--id] <TRIM_ID>
+   [--size] <SIZE>
+```
+
+DESCRIPTION
+-----------
+
+Provides a mechanism to trim older events from the event store.
+
+OPTIONS
+-----------
+**--trim-id**
+
+: event id to trim up to and including
+
+**--size**
+
+: trim and keep up to size events
+
+Note: if both the --trim-id and --size options are specified, both trim
+operations will be performed.
+
+ACCESS
+------
+Any user who has administrate server capabilities and has configured an SSH key.
+
+SCRIPTING
+---------
+This command is intended to be used in scripts, perhaps to be called by a
+cron job.