Merge multiple Git repositories for Advent of Code (AOC) into a single one

merge.sh

#!/bin/bash

# Goal:
# Merge multiple repos into one with a separate subdirectory for each source
# repo and interleaved commit history. Wouldn't work well for repos with a lot
# of merges and parallel history, but should work well for these mostly
# chronological repos.
# 
# Inspired from https://dev.to/detunized/git-fu-merge-multiple-repos-with-linear-history-4kci
# With changes:
# - Use git filter-repo instead

set -euo pipefail

repos="2018:https://github.com/robinst/advent-of-code-2018
2019:https://github.com/robinst/advent-of-code-2019
2020:https://github.com/robinst/advent-of-code-2020
2022:https://github.com/robinst/advent-of-code-2022
2023:https://github.com/robinst/advent-of-code-2023"

# Clone and filter all individual repos
for repo in $repos; do
    path=${repo%%:*}
    url=${repo#*:}
    if [ ! -e "$path" ]; then
        git clone --mirror "$url" "$path"
        (cd "$path" && git filter-repo \
            --to-subdirectory-filter "$path" \
            --message-callback "return b\"$path: \" + message")
    fi
done

rm -rf merged
git init merged
cd merged

# Fetch into merged repo
for repo in $repos; do
    path=${repo%%:*}
    git fetch ../$path HEAD
    git branch $path FETCH_HEAD
done

# Make history linear
for i in $(git log --pretty='%H' --author-date-order --reverse --all); do
    GIT_COMMITTER_DATE=$(git log -1 --pretty='%at' $i) git cherry-pick $i
done

remove-inputs.sh

cd merged

# Remove inputs from merged repository to store in a separate private repository
git filter-repo --invert-paths \
  --path 2019/input \
  --path 2020/input \
  --path 2022/java/src/test/resources \
  --path 2022/swift/Sources/AOC2022/Resources \
  --path 2022/src/test/resources \
  --path-glob '*/input.txt' \
  --force