post-checkout.sh

#! /bin/bash

PREV_HEAD=$1
HEAD=$2
BRANCH_CHECKOUT=$3

# Skip the hook if the checkout is not a branch checkout.
[ "$BRANCH_CHECKOUT" = 1 ] || exit 0

# Tells wether a file has been modified between 'PREV_HEAD' and 'HEAD'.
was_modified() {
  ! git diff-tree -r --quiet --diff-filter=M $PREV_HEAD $HEAD -- $1
}

# Runs a command in the background.
# If the command fails, its output is written to the provided path.
run_in_background() {
  command="$1"
  log_path="$2"
  (
    if ! output=$(eval "$command" 2>&1); then
      [ -z "$log_path" ] || echo "$output" > $log_path
    fi &
  )
}

if was_modified Gemfile.lock && was_modified db/structure.sql; then
  echo 'Running `bundle && rake:db migrate` in the background...'
  run_in_background 'bundle && rake db:migrate && git checkout db/structure.sql' db-migrate-error.log
elif was_modified Gemfile.lock; then
  echo 'Running `bundle` in the background...'
  run_in_background 'bundle' bundle-error.log
elif was_modified db/structure.sql; then
  echo 'Running `rake:db migrate` in the background...'
  run_in_background 'rake db:migrate && git checkout db/structure.sql' db-migrate-error.log
fi

if was_modified yarn.lock; then
  echo 'Running `yarn` in the background...'
  # TODO: use --mutex
  run_in_background 'yarn --no-emoji'
fi