build_monorepo

#!/bin/bash

set -x
set -e

here=$(dirname $(realpath "$0"))

dir="$1"
mirrors="$2"

function incorporate {
    name=$1
    url=$2

    before=$(git log --all --oneline | wc -l)

    git remote add "$name" "$url"
    git config --local "remote.$name.fetch" "+refs/heads/*:refs/heads/$name/*"
    git config --local --add "remote.$name.fetch" "+refs/tags/*:refs/tags/$name/*"
    git fetch --no-tags "$name"
    git remote remove "$name"

    after=$(git log --all --oneline | wc -l)

    newlogs=$((after - before))
    echo "After incorporating $name $newlogs changes."
}

function pushdown {
    name=$1
    branch=$2

    if [ ! -z "$(git show-ref "$branch")" ]; then

        echo "Pushing $branch into $name."

        git switch -c pushdown "$branch"
        dir=$(mktemp -d tmp.XXXX)
        moved_something="false"
        for f in * .*; do
            if [[ "$f" != .git && "$f" != "$dir" && "$f" != "." && "$f" != ".." ]]; then
                git mv "$f" "$dir"
                moved_something="true"
            fi
        done
        if [ "$moved_something" == "true" ]; then
            git mv "$dir" "$name"
        else
            mv "$dir" "$name"
            echo "No files in master branch." > "$name/empty-master.txt"
            git add "$name/empty-master.txt"
        fi
        git commit  --allow-empty -m "Moving $name to subdir."
        git checkout master
        git merge --allow-unrelated-histories -s recursive -X no-renames --no-ff -m "Merging $name to master." pushdown
        git branch -d pushdown

        echo "Done pushing $branch into $name."
        sleep 1
    else
        echo "No branch $branch to merge into master."
        git show-ref | grep "refs/heads/$name"
    fi
}


mkdir -p "$dir"
cd "$dir"
if [ ! -d ".git" ]; then
    git init
    git commit --allow-empty -m "Creating combined repo."
    sleep 1
fi

# Incorporate constituent repos and combine into master branch
ls -d "$here"/"$mirrors"/*.git | sort | while read -r repo; do
    if git --git-dir "$repo" show-ref; then
        name=$(basename "$repo" .git)
        echo "Incorporating $name ..."
        incorporate "$name" "$repo"
        pushdown "$name" "$name"/master
    else
        echo "Skipping empty repo $repo."
    fi
done