Update Dockerfile to use opam 2

A big difference with the previous Dockerfile is that this container
holds the new learn-ocaml program, not the full web-app: it should be
run with a local exercises repository.

This could be used as base for a container including the exercises
though, possibly using Docker multi-stage.

Build the image using `make docker-image`

Dockerfile

@@ -1,23 +1,26 @@
-FROM ocaml/opam
-
-RUN cd /home/opam/opam-repository && git pull
-
-RUN opam config exec -- opam update
+FROM ocaml/opam2-staging:alpine
+LABEL Description="learn-ocaml running container" Vendor="OCamlPro" Version="0.1"
 
 WORKDIR learn-ocaml
 
-COPY src/opam src/opam
-COPY scripts/install-opam-deps.sh scripts/install-opam-deps.sh 
-COPY Makefile Makefile
+COPY learn-ocaml.opam .
+RUN sudo chown opam:nogroup learn-ocaml.opam
 
-RUN opam config exec -- make build-deps
-
-COPY . .
+ENV OPAMYES true
+RUN opam switch 4.05
+RUN opam pin learn-ocaml . -n
+RUN opam depext learn-ocaml
+RUN opam install . --deps-only --locked
 
+ADD . .
 RUN sudo chown -R opam:nogroup .
 
-RUN opam config exec -- make REPO_DIR=exercises_repository
+RUN opam install .
+
+ARG port=8080
+ENV port=${port}
 
-EXPOSE 9090
+EXPOSE $port
 
-CMD ["/home/opam/learn-ocaml/learnocaml-simple-server.byte", "-port", "9090" ]
+CMD ["build","serve"]
+ENTRYPOINT ["/bin/bash","-c","opam exec -- learn-ocaml --sync-dir=/sync --repo=/repository --port=${port} \"$@\""]

Makefile

@@ -79,6 +79,13 @@ update-%-translation: translations/%.pot
 opaminstall: build learn-ocaml.install
 	@opam-installer --prefix `opam var prefix` learn-ocaml.install
 
+docker-image: Dockerfile learn-ocaml.opam
+	@rm -rf docker
+	@git clone . docker
+	@cp Dockerfile docker
+	@docker build -t learn-ocaml docker
+	@echo "Use with 'docker run --rm -v \$$PWD/sync:/sync -v \$$PWD:/repository -p PORT:8080 learn-ocaml -- ARGS'"
+
 clean:
 	@ocp-build clean
 	-rm -f translations/$*.pot