# The one image a match runs in: a JDK to host MegaMek, and a Python to run the
# bot the host spawns as a subprocess.
#
# There is no JDK on the development machine here and no intention of installing
# one - the sibling repos (helm/bridge, ~/.cache/mul-build) all reach for a
# throwaway container instead. This is that, plus the interpreter the stub bot
# needs, because the bot is a child process of the JVM and has to exist wherever
# the JVM does.
#
# MegaMek itself is NOT in the image. It is mounted at run time from an
# extracted release, so bumping MegaMek does not mean rebuilding this, and so
# this repository ships none of MegaMek's CC BY-NC-SA data.
FROM eclipse-temurin:21-jdk

# python3 only - no pip, no venv. The bot protocol is newline JSON on a pipe and
# the stub bot uses the standard library, so a dependency here would be a
# dependency in every match container forever. A bot that needs more brings its
# own image.
#
# The X11 libraries are for `sds play`, where a person sits at MegaMek's own
# Swing client with the display forwarded to the host's X server. A JDK image
# ships libawt_xawt.so but none of the libraries it links against, so without
# these every AWT call fails with UnsatisfiedLinkError; `ldd` on that file is
# the list. x11-utils is xdpyinfo, which is how `sds play --check-display`
# answers "can this container reach your X server" without starting a match.
# Nothing on the batch path loads any of it - that path still runs with
# -Djava.awt.headless=true and never touches AWT.
#
# xvfb and xauth are for `one --replay`, which has no host display to borrow.
# MegaMek's minimap renderer ends in ImageUtil.createAcceleratedImage(Image),
# which returns null when AWT has no screen device - so every one of its image
# factories hands back null under headless, having drawn the picture correctly
# first. A frame buffer is the smallest thing that makes stock MegaMek code
# work unmodified; the alternative was reflecting into MinimapPanel's private
# drawing methods. A match without --replay still runs headless and never
# starts an X server.
RUN apt-get update \
 && apt-get install --no-install-recommends -y \
      python3 \
      libx11-6 libxext6 libxrender1 libxtst6 libxi6 \
      libfreetype6 fontconfig fonts-dejavu-core \
      x11-utils xvfb xauth \
 && rm -rf /var/lib/apt/lists/*

ENV PYTHONUNBUFFERED=1
WORKDIR /work