#!/usr/bin/env bash
# Fetch and unpack a MegaMek release, which is the thing this repository reads
# and deliberately does not contain.
#
#   ./scripts/fetch-megamek.sh 0.51.0
#   ./scripts/fetch-megamek.sh 0.51.0 /somewhere/else
#
# Prints the install path on stdout, so it composes:
#
#   MM_HOME="$(./scripts/fetch-megamek.sh 0.51.0)"
#
# It gets you the unit files, the art and the jar. It does not get you the
# equipment catalogue: that is computed when MegaMek loads, comes out through
# bridge/dump.sh, and needs a container. Every command here that prices a
# design needs both, and says so.
#
# The digest is not optional and not ours to invent. Upstream publishes none,
# so the table below holds digests taken from a fetch that was checked twice,
# and a version that is not in it needs one passed in rather than being
# trusted:
#
#   HELM_MEGAMEK_SHA256=<digest> ./scripts/fetch-megamek.sh 0.52.0
#
# arena pins the same release for the container a match runs in, in its
# versions.env, and the digest here for 0.51.0 is that one. When they differ,
# the match and the library are describing different games.
set -euo pipefail

usage() {
  echo "usage: scripts/fetch-megamek.sh <version> [install-dir]"
}

# Releases this repository has been run against, and the digest of each
# release tarball. Add a line when a version is taken, from a fetch you trust.
sha256_for() {
  case "$1" in
    0.51.0) echo "5d673cdaca0ead0e58d6e74db5b2d1e06bc25ccb5caaf332dad71624f6487b85" ;;
    *) echo "" ;;
  esac
}

version="${1:-}"
if [ -z "$version" ]; then
  usage >&2
  exit 2
fi
if [ "$version" = "-h" ] || [ "$version" = "--help" ]; then
  usage
  exit 0
fi

cache="${XDG_CACHE_HOME:-$HOME/.cache}/helm/megamek"
dest="${2:-$cache/$version}"
mkdir -p "$cache"

# Already unpacked: say where and stop. The tree is 590MB and a release's bytes
# never change, so re-fetching one is only ever wasted time.
if [ -f "$dest/MegaMek.jar" ] && [ -d "$dest/data/mekfiles" ]; then
  echo "already unpacked" >&2
  echo "$dest"
  exit 0
fi

sha256="${HELM_MEGAMEK_SHA256:-$(sha256_for "$version")}"
[ -n "$sha256" ] || {
  echo "no digest known for MegaMek $version." >&2
  echo "  Upstream publishes none, so take one from a fetch you trust and pass it:" >&2
  echo "    HELM_MEGAMEK_SHA256=<digest> $0 $version" >&2
  echo "  then add it to sha256_for() in this script." >&2
  exit 1
}

url="https://github.com/MegaMek/megamek/releases/download/v${version}/MegaMek-${version}.tar.gz"
tarball="$cache/MegaMek-${version}.tar.gz"

# Kept, and checked whether it was kept or fetched. The release is 639MB and
# the check is what makes a cached copy safe to believe.
if [ -f "$tarball" ] && echo "$sha256  $tarball" | sha256sum -c --status -; then
  echo "using $tarball" >&2
else
  echo "fetching $url" >&2
  # A progress meter for a person watching 609MB arrive, and nothing at all
  # when this is a step inside something else.
  quiet=""
  [ -t 2 ] || quiet="-s"
  # To a partial name, moved into place only once the digest checks, so an
  # interrupted download is never mistaken for a release.
  # shellcheck disable=SC2086 # $quiet is one flag or nothing, deliberately
  curl -fSL $quiet --retry 3 --retry-connrefused -o "$tarball.part" "$url"
  if ! echo "$sha256  $tarball.part" | sha256sum -c --status -; then
    rm -f "$tarball.part"
    echo "digest mismatch for MegaMek $version" >&2
    echo "  expected $sha256" >&2
    echo "  refusing to unpack a tarball that is not the pinned release" >&2
    exit 1
  fi
  mv "$tarball.part" "$tarball"
fi

# Upstream's tarball does not spell the version the way the tag does — 0.51.0
# unpacks as MegaMek-0.51.00 — so the directory is found rather than assumed.
staging="$(mktemp -d "$cache/unpack.XXXXXX")"
trap 'rm -rf "$staging"' EXIT
tar -xzf "$tarball" -C "$staging"
root="$(find "$staging" -maxdepth 1 -type d -name 'MegaMek-*' | head -1)"
[ -n "$root" ] || {
  echo "no MegaMek-* directory in the tarball; upstream changed its layout" >&2
  exit 1
}

mkdir -p "$(dirname "$dest")"
rm -rf "$dest"
mv "$root" "$dest"

echo "unpacked MegaMek $version into $dest" >&2
echo >&2
echo "Reading the library needs nothing else:" >&2
echo "  cargo build --release" >&2
echo "  ./target/release/helm art --megamek $dest --out art.json" >&2
echo >&2
echo "Anything that prices a design also needs the equipment catalogue, which" >&2
echo "MegaMek computes at load time. That is what the bridge is for, and it" >&2
echo "runs a JDK in a container:" >&2
echo "  ./bridge/dump.sh $dest /tmp/helm-bridge" >&2
echo "  ./target/release/helm index --megamek $dest --bridge-dir /tmp/helm-bridge --out units.json" >&2
echo "$dest"