Basic Docker syncer configuration

First version of Docker config to search for all available videos and
sync them to bind mounted folder at /home/appuser/Tablo. Some hacks to
enable functioning in Synology DSM 7.2's Container Manager. Assumes that
Tablo directory has already been configured with a command like:

> ./tut.py config --discover

Tested it locally in MacOS with Tablo mounted shared folder:

> docker build -t pvulgaris/tut-syncer:arm64 .
> docker run --name tut-syncer --mount type=bind,source=/Volumes/video/Tablo,target=/home/appuser/Tablo pvulgaris/tut-syncer:arm64

Then build amd64 version for upload to Docker Hub and use on DS224+:

> docker buildx build -t pvulgaris/tut-syncer:amd64 --platform linux/amd64 .

Finally, use the DSM api to setup a job with Task Scheduler as described
in https://www.reddit.com/r/synology/comments/10wkxuc/restart_docker_container/

Author: pvulgaris

Dockerfile

@@ -14,20 +14,31 @@ ENV PYTHONDONTWRITEBYTECODE=1
 # the application crashes without emitting any logs due to buffering.
 ENV PYTHONUNBUFFERED=1
 
+# Install ffmpeg libraries needed to transcode Tablo video files.
+RUN apt-get update && apt-get install -y ffmpeg
+
 WORKDIR /app
 
 # Create a non-privileged user that the app will run under.
 # See https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#user
-ARG UID=10001
+# Default Synology DSM first uid. See comments below for more context.
+# TODO: Make uid and gid easier to configure parameters.
+ARG UID=1026
 RUN adduser \
     --disabled-password \
     --gecos "" \
-    --home "/nonexistent" \
     --shell "/sbin/nologin" \
-    --no-create-home \
     --uid "${UID}" \
     appuser
 
+# GID hacks for Synology DSM. Try as best we can to replicate DSM's default
+# primary ("100(users)") and secondary group membership ("101(administrators)")
+# to overcome permission issues with writing to a bind mounted folder, while
+# still being somewhat platform agnostic. Example of the issue:
+# https://www.reddit.com/r/synology/comments/s1arg0/synology_and_docker_permission_problem/
+RUN usermod -g users appuser
+RUN adduser appuser `cat /etc/group | grep ":101:" | cut -d':' -f1`
+
 # Download dependencies as a separate step to take advantage of Docker's caching.
 # Leverage a cache mount to /root/.cache/pip to speed up subsequent builds.
 # Leverage a bind mount to requirements.txt to avoid having to copy them into
@@ -42,8 +53,14 @@ USER appuser
 # Copy the source code into the container.
 COPY . .
 
-# Expose the port that the application listens on.
-EXPOSE 8000
+# Build the shows db.
+# TODO: Run this separately for now.
+# RUN python3 tut.py config --discover
 
-# Run the application.
-CMD python3 tut.py
+# Check if ~/Tablo directory is mounted. Ideally this is run before each tut.py
+# command (or tut.py is modified to not implicitly create a ~/Tablo directory)
+# so that we don't accidentally sync shows into the container.
+# TODO: Also check we have the right read/write permissions.
+# Then sync all shows.
+CMD if [ ! -d "/home/appuser/Tablo" ]; then echo "/home/appuser/Tablo not mounted." && exit 1; fi; \
+  python3 tut.py library --build && python3 tut.py -L search | python3 tut.py copy