#!/bin/bash
#
# Save/restore your .git/config files in a central place.
#
# When called as "git-config-save" or "git config-save",
# this scripts traverses a folder looking for all .git/config files
# and makes backups at ~/.config/gitconfigs.
#
# When called as "git-config-restore" or "git config-restore"
# it does the reverse operation: restores all .git/config
# files, replacing the current repository .git/config's by the one
# available from ~/.config/gitconfigs.
#
# Use cases:
#
#   - You work with the repositories in multiple machines and is
#     looking for a way to sync not just the content but also the
#     same repository configuration (user name, remotes, etc).
#
#   - You want to delete working copies of repositories but want
#     to keep each repository configuration for future use. In that
#     case all you have to do is to clone the repository again and
#     run this command inside your working copy.
#
# You may want to put in a schedule job to process all your stuff regularly.
#
# Storage format:
#
#   - Use ~/.config/gitconfigs/ as base.
#   - Repository identifier is determined by it's path in the system.
#     That's the best choice if you have the same repository checked out
#     multiple times and with different configurations.
#   - Repository identifier can also be determined by the first commit ID
#     (not repo URL or any other volatile information). So this
#     script may fail if you're doing improbable stuff like rebasing
#     your repo and removing the initial commit.
#
# How it saves an item:
#
#   - Find all git configurations.
#   - Make a backup at $BASE/$ID/config.$DATE if config differs.
#   - Save the config at $BASE/ID.
#
# How it restore an item:
#
#   - Copy each config from $BASE/ID, if available and if it differs.
#   - Restore always save a timestamped copy at .git/config.$DATE.

# Parameters
BASENAME="`basename $0`"
BASE="$HOME/.config/gitconfigs"
DATE="`date +%Y%m%d%I%M%S`"
FILENAME="gitconfig.saved"
OPTION="$1"
COUNTER="$BASE/counter"
SOMETIMES="20"

# Ensure we have a base and that is minimally safe
mkdir -p  $BASE
chmod 700 $BASE

# Save config from a repository
function git_config_save {
  # Check if we have a config
  if [ ! -e ".git/config" ]; then
    echo "$BASENAME: missing config at `pwd`"
    return
  fi

  # Repository ID
  # https://stackoverflow.com/questions/34874343/how-can-i-uniquely-identify-a-git-repository
  #ID="`git rev-list --parents HEAD | tail -1`"
  ID="$PWD"

  # Display ID
  #echo $ID

  # Create config folder
  mkdir -p $BASE/$ID

  # Make a backup
  if [ -f "$BASE/$ID/$FILENAME" ] && ! diff .git/config $BASE/$ID/$FILENAME &> /dev/null; then
    echo "Differences detected at `pwd`, making a backup..."
    cp $BASE/$ID/$FILENAME $BASE/$ID/$FILENAME.$DATE
  fi

  # Save
  cp .git/config $BASE/$ID/$FILENAME
}

# Restore config tor a repository
function git_config_restore {
  # Check if we have a config
  if [ ! -e ".git/config" ]; then
    echo "$BASENAME: missing config at `pwd`"
    return
  fi

  # Repository ID
  # https://stackoverflow.com/questions/34874343/how-can-i-uniquely-identify-a-git-repository
  #ID="`git rev-list --parents HEAD | tail -1`"
  ID="$PWD"

  # Display ID
  #echo $ID

  # Create config folder
  mkdir -p $BASE/$ID

  # Check if we have a saved config
  if [ ! -f "$BASE/$ID/$FILENAME" ]; then
    echo "No config for `pwd`, skipping"
    return
  fi

  # Make a backup
  if ! diff .git/config $BASE/$ID/$FILENAME &> /dev/null; then
    cp .git/config .git/config.$DATE
  else
    echo "Identical configs for `pwd`, skipping"
    return
  fi

  # Restore
  cp $BASE/$ID/$FILENAME .git/config

  # Tell the user about the backup
  echo "Backup saved at $pwd/.git/config.$DATE"
}

# Check option
if [ ! -z "$OPTION" ] && [ "$OPTION" == "--sometimes" ]; then
  if [ ! -e "$COUNTER" ]; then
    echo 0 > $COUNTER
  fi

  COUNT="`cat $COUNTER`"

  if (($COUNT >= $SOMETIMES)); then
    echo 0 > $COUNTER
  else
    let COUNT++
    echo $COUNT > $COUNTER
    echo "Running only sometimes. This is run ${COUNT} of ${SOMETIMES}, skipping."
    exit 1
  fi
fi

# Process everything we can find
find -type d -name .git | while read repo; do
  # Get absolute folder
  PWD="`cd $repo/.. &> /dev/null && pwd`"

  #echo -n -e "Processing $PWD...\t"
  echo "Processing $PWD..."

  (
  cd $PWD

  if [ "$BASENAME" == "git-config-save" ]; then
    git_config_save
  else
    git_config_restore
  fi
  )
done