docker: merge config from example on boot

docker-entrypoint.sh

@@ -9,6 +9,7 @@ BUNDLED_EXAMPLE_PATH="${INSTALL_DIR}/config.yaml.example"
 RUNTIME_USER="${USER:-repeater}"
 RUNTIME_UID="${PUID:-unknown}"
 RUNTIME_GID="${PGID:-unknown}"
+YQ_CMD="${YQ_CMD:-/usr/local/bin/yq}"
 
 mkdir -p "${CONFIG_DIR}"
 
@@ -22,6 +23,52 @@ copy_or_die() {
     fi
 }
 
+merge_config_from_example() {
+    config_path="$1"
+
+    if [ ! -f "${config_path}" ] || [ ! -f "${EXAMPLE_PATH}" ]; then
+        return 0
+    fi
+
+    if [ ! -x "${YQ_CMD}" ] || ! "${YQ_CMD}" --version 2>&1 | grep -q "mikefarah/yq"; then
+        echo "Skipping config merge: mikefarah yq is not available at ${YQ_CMD}." >&2
+        return 0
+    fi
+
+    tmpdir="$(mktemp -d)"
+    stripped_user="${tmpdir}/config.stripped.yaml"
+    merged_config="${tmpdir}/config.merged.yaml"
+
+    cleanup_merge() {
+        rm -rf "${tmpdir}"
+    }
+    trap cleanup_merge EXIT HUP INT TERM
+
+    # Keep only the example's comments to avoid comment duplication across upgrades.
+    "${YQ_CMD}" eval '... comments=""' "${config_path}" > "${stripped_user}" 2>/dev/null || cp "${config_path}" "${stripped_user}"
+
+    if ! "${YQ_CMD}" eval-all '. as $item ireduce ({}; . * $item)' "${EXAMPLE_PATH}" "${stripped_user}" > "${merged_config}" 2>/dev/null; then
+        echo "Failed to merge ${config_path} with ${EXAMPLE_PATH}; keeping the existing config." >&2
+        cleanup_merge
+        trap - EXIT HUP INT TERM
+        return 0
+    fi
+
+    if ! "${YQ_CMD}" eval '.' "${merged_config}" >/dev/null 2>&1; then
+        echo "Merged config for ${config_path} is invalid; keeping the existing config." >&2
+        cleanup_merge
+        trap - EXIT HUP INT TERM
+        return 0
+    fi
+
+    if ! cmp -s "${config_path}" "${merged_config}"; then
+        copy_or_die "${merged_config}" "${config_path}"
+    fi
+
+    cleanup_merge
+    trap - EXIT HUP INT TERM
+}
+
 if [ ! -f "${EXAMPLE_PATH}" ] && [ -f "${BUNDLED_EXAMPLE_PATH}" ]; then
     copy_or_die "${BUNDLED_EXAMPLE_PATH}" "${EXAMPLE_PATH}"
 fi
@@ -35,4 +82,6 @@ elif [ ! -s "${CONFIG_PATH}" ] && [ -f "${EXAMPLE_PATH}" ]; then
     copy_or_die "${EXAMPLE_PATH}" "${CONFIG_PATH}"
 fi
 
+merge_config_from_example "${CONFIG_PATH}"
+
 exec python3 -m repeater.main --config "${CONFIG_PATH}"