Addresses OpenHistoricalMap/issues#786 by adding a new workflow and a…

…ssociated bash script.

.github/workflows/ohm.upstream-sync.yml

@@ -0,0 +1,20 @@
+name: Upstream Sync
+
+on:
+  schedule:
+    - cron: "20 5,17 * * *"
+  workflow_dispatch:
+
+jobs:
+  upstream-sync:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: ./scripts
+    steps:
+      - name: Check out the repository to the runner
+        uses: actions/checkout@v4
+      - name: Make the script files executable
+        run: chmod +x upstream_sync.sh
+      - name: Run sync script
+        uses: upstream_sync.sh

scripts/upstream_sync.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+
+#
+#
+#
+
+git checkout main
+git branch -D the-sacrifice
+git checkout -b the-sacrifice
+git fetch upstream master
+
+mkdir upstream
+for i in $(git ls-tree upstream/master --name-only); do
+  if [[ $i == *.md ]];then
+    git show upstream/master:$i > upstream/$i
+  fi
+done
+git show upstream/master:LICENSE > upstream/LICENSE
+git add upstream
+git commit -m 'Preserving upstream markdown & text files.'
+
+git merge --no-ff --no-commit upstream/master
+concerns=('js/ide.js' 'js/map.ts')
+for i in $(git diff --name-only --diff-filter=U --relative);do
+  echo "$i"
+  for c in "${concerns[@]}";do
+    echo "$c"
+    if [[ $i != $c ]];then
+      git checkout --theirs -- $i
+      git add $i
+    fi
+  done
+done
+
+iso=$(date -Iminutes)
+git commit -m "Merge upstream ("$iso")."