#!/bin/bash
# vim: set syntax=sh:
set -e

# sshok is a simple tool for managing a user's SSH configuration, allowing for a simpler and saner
# way of storing large SSH configuration sets.
#
# Just put any groups of settings inside $SSH_CONFIG_DIR (defaults to $HOME/.ssh/config) and use
# this script instead of `ssh` to perform any SSH task.
#
# This script will take any files inside $SSH_CONFIG_DIR and concatenate them into $SSH_CONFIG_FILE
# so that the SSH configuration can be split into different files for easier management. This
# script can be thought of as an SSH wrapper, which first determines whether the configuration file
# needs to be updated, updates it (according to what has been determined) and then runs the
# original ssh command with any argument provided to this script.
#
# Every time this script determines it needs to update the $SSH_CONFIG_FILE, it will backup the
# current configuration first and then overwrite the file. Backups have two levels: a first one,
# thought for quick restores which only keeps the last configuration in a file stored alongside
# the $SSH_CONFIG_FILE and suffixed with ".bak", and a second one which is thought for keeping a
# larger log of the different versions of the configuration file, which will back up every version
# of the $SSH_CONFIG_FILE to $BACKUPS_DIR, suffixing each version with the timestamp of the moment
# when the backup was made. This means that if anything should go wrong, a previous version of the
# configuration could be restored.
#
# This file is intended to work as a self-documented script, so please do read the comments in it
# as they aim at guiding anyone looking at it.

# The following variables indicate where are located the source files and the target configuration
# file, and can be overridden by setting their values in environment variables before running
# this script. This is a pretty simple way of allowing the customization of the scripts' default
# behavior.
#
# For instance, the script could be run like follows to store the resulting configuration file in
# an alternative location if your SSH installation differs from the standard one, or if you would
# like to test the outcome of running this script, or even if you would like to generate an SSH
# config file to share with your SO:
#
#   $ SSH_CONFIG_FILE=/tmp/my_ssh_config sshok
SSH_DIR=${SSH_DIR:-$HOME/.ssh}
SSH_CONFIG_DIR=${SSH_CONFIG_DIR:-$SSH_DIR/config.d}
SSH_CONFIG_FILE=${SSH_CONFIG_FILE:-$SSH_DIR/config}
BACKUPS_DIR=${BACKUPS_DIR:-/tmp/sshok}
UNWANTED_FILES_PATTERN="# vim:"
# Sometimes you need to share configuration files with different, unrelated groups thus creating
# the need to more than a single config directory. For instance, working on 2 different projects
# with people unrelated between them -- imagine two directories, "job1" and "job2", one for each
# project:
# SSH_CONFIG_DIRS="$HOME/job1 $HOME/job2 ${SSH_CONFIG_DIR}"
# The default value for SSH_CONFIG_DIRS is $SSH_CONFIG_DIR.
SSH_CONFIG_DIRS="${SSH_CONFIG_DIRS:-$SSH_CONFIG_DIR}"


# Get the filename with the most recently mtime from the path passed in the first argument. $1 is
# expected to exist.
newest_file_in() {
  if [ -e $1 ]; then
    stat=$(determine_stat_variation $1)
    if [ $stat = "-c" ]; then
      find -L $SSH_CONFIG_DIRS -type f -print0 | xargs -0 stat -c '%Y %n' | sort -rn | head -1 | cut -d' ' -f2
    else
      find -L $SSH_CONFIG_DIRS -type f -print0 | xargs -0 stat -f '%m %N' | sort -rn | head -1 | cut -d' ' -f2
    fi
  fi
}

# Determine which arguments stat can handle. This is due to a difference in the expected args for
# that command between Linux and OS X.
determine_stat_variation() {
  set +e
  stat -c %Y $1 >/dev/null 2>&1
  if [ $? -eq 0 ]; then
    # Linux' stat
    echo "-c"
  else
    # OS X/BSD's stat
    echo "-f"
  fi
  set -e
}

# Backs up the file passed in the first argument to a file named {name}.{current_timestmap} inside
# the path passed in as second argument, and to {name}.bak (the latter will overwrite any existing
# backup).
backup_config() {
  if [ -f $1 ]; then
    cp $1 "$BACKUPS_DIR/$(basename $1).$(date +%s)"
    cp -f $1{,.bak}
  fi
}

# Print to stdout the configuration resulting from the concatenation of every file in the path
# passed in the first argument.
generate_config() {
  echo -e "#\n# This file was autogenerated from $1 on $(date +%FT%T)\n#\n"
  for dir in $SSH_CONFIG_DIRS; do
	for file in $dir/*; do
    		echo "# From $file"
    		cat $file | grep -v "$UNWANTED_FILES_PATTERN"
  	done
  done	
}

# First, make sure the $SSH_CONFIG_DIR directory exists and if it doesn't copy the current
# $SSH_CONFIG_FILE to it. By doing that we won't overwrite the existing configuration by accident
# on the first run.
if [ ! -d $SSH_CONFIG_DIR ]; then
  mkdir -p $SSH_CONFIG_DIR 
  if [ -f $SSH_CONFIG_FILE ]; then   
  	cp $SSH_CONFIG_FILE $SSH_CONFIG_DIR/original
  else
  	echo -e "#\n# This file was autogenerated from $1 on $(date +%FT%T)\n#\n" > $SSH_CONFIG_FILE
  fi
fi



if [ ! -d $BACKUPS_DIR ]; then
  mkdir -p $BACKUPS_DIR
fi

# Only if the autogenerated config file is older than the source ones inside the $SSH_CONFIG_DIR,
# regenerate the configuration on $SSH_CONFIG_FILE.
if [ ! -e $SSH_CONFIG_FILE ] || [ $(newest_file_in $SSH_CONFIG_DIR) -nt $SSH_CONFIG_FILE ]; then
  # Backup current config...
  backup_config $SSH_CONFIG_FILE $BACKUPS_DIR
  # ...and then generate the new one
  generate_config $SSH_CONFIG_DIRS > $SSH_CONFIG_FILE
fi

# Finally, run ssh with any arguments passed to this script
ssh $@