new: [compose-core] provide ``get_healthy_container_ip_for_service`` and ``switch_to_relation_service`` to charms base library

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>

bin/compose-core

@@ -3103,6 +3103,65 @@ get_running_compose_containers() {
 export -f get_running_compose_containers
 
 
+get_healthy_container_ip_for_service () {
+    local service="$1" port="$2" timeout=${3:-60}
+
+    local containers container container_network container_ip
+
+    containers="$(get_running_containers_for_service "$service")"
+
+    if [ -z "$containers" ]; then
+        err "No containers running for service $DARKYELLOW$service$NORMAL."
+        exit 1
+    fi
+
+    ## XXXvlab: taking first container is probably not a good idea
+    container="$(echo "$containers" | head -n 1)"
+
+    ## XXXvlab: taking first ip is probably not a good idea
+    read-0 container_network container_ip < <(get_container_network_ip "$container")
+
+    if [ -z "$container_ip" ]; then
+        err "Can't get container's IP. You should check health of" \
+            "${DARKYELLOW}$service${NORMAL}'s container."
+        exit 1
+    fi
+
+    wait_for_tcp_port "$container_network" "$container_ip:8069" 4 || {
+        err "TCP port of ${DARKYELLOW}$service${NORMAL}'s container doesn't seem open"
+        echo "  Please check that container is healthy. Here are last logs:" >&2
+        docker logs "$container" --tail=10 | prefix "  ${GRAY}|${NORMAL} " >&2
+        exit 1
+    }
+    info "Host/Port ${container_ip}:${port} checked ${GREEN}open${NORMAL}."
+    echo "$container_network:$container_ip"
+}
+export -f get_healthy_container_ip_for_service
+
+
+switch_to_relation_service() {
+    local relation="$1"
+
+    ## XXXvlab: can't get real config here
+    if ! read-0 ts _ _ < <(get_service_relation "$SERVICE_NAME" "$relation"); then
+        err "Couldn't find relation ${DARKCYAN}$relation${NORMAL}."
+        exit 1
+    fi
+
+    export SERVICE_NAME="$ts"
+    export SERVICE_DATASTORE="$DATASTORE/$SERVICE_NAME"
+    DOCKER_BASE_IMAGE=$(service_base_docker_image "$SERVICE_NAME")
+    export DOCKER_BASE_IMAGE
+
+    target_charm=$(get_service_charm "$ts") || exit 1
+    target_charm_path=$(charm.get_dir "$target_charm") || exit 1
+
+    cd "$target_charm_path"
+
+}
+export -f switch_to_relation_service
+
+
 get_volumes_for_container() {
     local container="$1"