Add downgrade functionality (contributed script)

contrib/downgrade.sh

@@ -0,0 +1,38 @@
+#!/bin/bash
+
+# Parameter check
+if [ -z "$1" ] || [ -z "$2" ]; then
+    echo "Syntax: $0 <source directory> <data directory>"
+    exit 1
+fi
+
+# Repository check
+if [ ! -d "$1/.git" ]; then
+    echo "This script can only downgrade Headphones installations via Git."
+    exit 1
+fi
+
+# Version file check
+if [ ! -s "$2/version.lock" ]; then
+    echo "Missing the version.lock file in the data folder, or the file is empty. Did you start Headphones at least once?"
+    exit 1
+fi
+
+# Git installation check
+if [ ! -x "$(command -v wget)" ]; then
+    echo "Git is required to downgrade."
+    exit 1
+fi
+
+# Display information
+HASH=$(cat $2/version.lock)
+
+echo "This script will try to downgrade Headphones to the last version that started, version $HASH. Make sure you have a backup of your config file and database, just in case!"
+echo "Press enter to continue, or CTRL + C to quit."
+read
+
+# Downgrade
+cd "$1"
+git reset --hard "$HASH"
+
+echo "All done, Headphones should be downgraded to the last version that started."