post-checkout

#!/bin/sh

# --- Command line
previous_head="$1"
new_head="$2"
branch_checkout="$3"

# --- Constants
separator="/"
master_branch="master"
main_backup="_backup"
database_name="db/beanstack_development"
# --- Functions

database_exists () {
  name=${1:0:63}
  return  `psql -U postgres -lqtA | cut -d\| -f1 | grep -qFx "$name"`
}

kill_connections() {
  psql -U postgres -c "SELECT pg_terminate_backend(pg_stat_activity.pid) FROM pg_stat_activity WHERE pg_stat_activity.datname = '$database_name' AND pid <> pg_backend_pid();" > /dev/null
}

duplicate_database_to() {
  name=${1:0:63}
  echo "Creating $name from $database_name"
  createdb -T $database_name $name
}

drop_database() {
  name=${1:0:63}
  echo "Deleting existing $name"
  dropdb -U postgres "$name"
}

rename_database() {
  old_name=${1:0:63}
  new_name=${2:0:63}
  psql -U postgres -c "SET standard_conforming_strings=on;" -q -b
  psql -U postgres -c "ALTER DATABASE \"$old_name\" RENAME TO \"$new_name\";" -q -e
  psql -U postgres -c "SET standard_conforming_strings=off;" -q -b
}

alias branch_name='git name-rev --name-only'

# --- Variables
previous_branch=`branch_name $previous_head`
new_branch=`git branch | grep -e "^*" | cut -d' ' -f 2`
old_database=$database_name$separator$previous_branch
new_database=$database_name$separator$new_branch
main_backup=$database_name$main_backup
# --- Script

if [ $branch_checkout -eq 0 ]; then
  exit 0 # Exit script if it is not a branch change
fi

echo "Switching from $previous_branch to $new_branch"
echo "Killing existing connections to $database_name"
kill_connections # We need to kill all the connections or the commands here will fail

if ! database_exists $main_backup; then
  echo "Creating a main_backup, if something goes wrong you can manually restore from this backup."
  duplicate_database_to $main_backup # We should always have a master backup
fi

if [ "$previous_branch" == "$new_branch" ]; then
  exit 0 # We didn't change branch, so lets just exit
fi

if database_exists $old_database; then
  # We need to remove old backups if they exists (they shouldn't most of the times) but
  # sometime when we didn't had changes in the branch when we created another one, so a
  # backup for the parent branch is created instead of one for the new branch, this is
  # to delete that wrong backup.
  drop_database $old_database
fi

if database_exists $new_database; then
  # When a backup for the new branch already exists
  # If there is already a backup for the branch we are checking to, lets just rename the active database to create a new backup
  rename_database $database_name $old_database
  # and then lets rename the existing backup to the active database name
  rename_database $new_database $database_name
else
  # If the branch we are checking to doesn't have a backup let's just copy the db to still have an active database
  duplicate_database_to $old_database
fi