Crude subdir to repository bridge

subdir-repo-bridge.sh

#!/bin/bash

# For our convenience since this is repeated
github_user="someuser"
our_label="loose-repo-name"

# Our local clone of the parent repo will be configured as a sparse checkout
# to check out only the specified subdir
parent_url=https://github.com/somebody/something.git
parent_branch=master
parent_dir="$HOME/src/${our_label}_parent"
parent_subdir="subdir/Something/"

# The child repo's basic layout is intended to mimic what would happen if
# you checked out the parent repo, copied its subdir to a new location, and
# started a new repo inside that copy.
child_url=git@github.com:$github_user/${our_label}.git
child_dir="$HOME/prj/${our_label}"
child_branch=upstream-master

bq='`'

create_empty_repo () {
	local_dir="$1"
	origin_url="$2"

	git init "$local_dir" &&
	(
		cd "$local_dir" &&
		git remote add origin "$origin_url"
	)
}

create_and_switch_to_branch () {
	local_dir="$1"
	branch="$2"

	(
		cd "$local_dir" &&
		git checkout -b "$branch"
	)
}

switch_to_branch () {
	local_dir="$1"
	branch="$2"

	(
		cd "$local_dir" &&
		git checkout "$branch"
	)
}

add_dir_to_sparse_checkout () {
	local_dir="$1"
	subdir="$2"

	(
		cd "$local_dir" &&
		git config core.sparsecheckout true &&
		echo "$subdir" >> .git/info/sparse-checkout
	)
}

clone_child_repo () {
    # Clone the child repo.
	# This will only work if the repo and branch both already exist.
    git clone -b "$child_branch" "$child_url" "$child_dir"
}

new_child_repo () {
	# Create a new repo for the child.
	# Avoid doing this if the repo and branch already exist.
	create_empty_repo "$child_dir" "$child_url" &&
	create_and_switch_to_branch "$child_dir" "$child_branch"
}

setup_parent_repo () {
	create_empty_repo "$parent_dir" "$parent_url" &&
	add_dir_to_sparse_checkout "$parent_dir" "$parent_subdir"
}


# To be run at least every time the child is updated in the parent
update () {
    # Update the parent repo
	echo "Updating local copy of parent repo" &&
    (
        cd "$parent_dir" &&
		git checkout "$parent_branch" &&
        git pull origin "$parent_branch" &&
        git clean -f -d -x
    ) &&

    # Replace child repo's files with the parent repo
	echo "Copying local parent over local child" &&
	switch_to_branch "$child_dir" "$child_branch" &&
    rsync -avz \
        --exclude README.md \
        --exclude .git \
        --delete "$parent_dir/$parent_subdir" "$child_dir/" &&

    # Think of a commit message
    current_date="`date -u -Iseconds`" &&
    commit_msg="Refreshed from $bq$parent_url$bq @ $bq$current_date$bq" &&

    # Check in and push the changes
    # (If nothing changed, no commit will occur)
	echo "Committing local child" &&
    (
        cd "$child_dir" &&
        git add -A &&
        git commit -m "$commit_msg" &&
		echo "Pushing local child" &&
        git push -u origin "$child_branch"
    )
}


# First run, if the child repo or branch doesn't exist yet remotely
#setup_parent_repo && new_child_repo && update

# First run, if the child repo or branch both exist remotely
#setup_parent_repo && clone_child_repo && update

# Subsequent runs
update