#!/bin/sh
#
# Copyright (C) 2013 Justin Edward Muniz <jmuniz@freebsd.org>
#
# Licensed under the GNU General Public License Version 2
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# Function: List and select from possible PackageKit backends
#
# There are three arguments that can be provided to this script:
#   Instruction: mandatory; can be either 'list' or 'set'
#   Backend Name: mandatory for 'set' instruction; a string that identifies the backend to use
#   Prefix: optional; if included, must be a valid prefix to the PackageKit installation path

# Determine if the prefix being used is an accurate PackageKit installation prefix
verifyPrefix() {
  # Make sure that the necessary configuration file exists given the prefix
  if [ ! -e "${PK_PREFIX}etc/PackageKit/PackageKit.conf" ]; then
    # Let the user know that the file was not found
    echo "Could not find PackageKit.conf, please check your prefix"
    # Advise user on usage
    printUsage
  fi
# End verifyPrefix
}

# Store either a provided or default installation prefix for later operations
setPrefix() {
  # Establish the default prefix
  PK_PREFIX="/usr/local/"
  # If there are three arguments, the last argument must be the prefix
  if [ $# -eq 3 ]; then
    # Assign the third argument to be the prefix
    PK_PREFIX="$3"
  # If there are two arguments and the instruction is "list" the last argument must be the prefix
  elif [ $# -eq 2 -a "$1" == "list" ]; then
    # Assign the second argument to be the prefix
    PK_PREFIX="$2"
  fi
  # The prefix must end in a slash (/) in order to be well-formed, test to see if the slash is missing
  # Evaluate the prefix to determine if it is well-formed
  case "${PK_PREFIX}" in
    # If the prefix ends with a slash
    *"/")
      # Do nothing, because the prefix appears to be well-formed
      ;;
    # For all other cases
    *)
      # Concatenate the slash onto the end of the prefix
      PK_PREFIX="${PK_PREFIX}/"
      ;; 
  esac
  # Make sure that the prefix provided is correct
  verifyPrefix
# End setPrefix
}

# Create a list consisting of backend options, each occupying one line and surrounded by spaces
generateBackendList() {
  # Until this is developed further, hardcode the option set
  PK_BACKENDS=" ports "$'\n'" pkgng "$'\n'" dummy "
# End generateBackendList
}

# Present the user with a list of available backends
listBackends() {
  # Make sure that the user has requested the backend list
  if [ "$1" == "list" ]; then
    # Generate a list of backends, demarcated by newlines
    generateBackendList
    # Print a header to describe the following data
    echo "Available PackageKit backends:"
    # Print the list of backends
    echo "${PK_BACKENDS}"
  fi
# End listBackends
}

# Configure PackageKit to use the chosen backend
setBackend() {
  # Make sure that the user wants to select the backend
  if [ "$1" == "set" ]; then
    # Generate the new-line demarcated list of backends
    generateBackendList
    # Determine if the backend provided is valid, each option is surrounded by spaces
    case "${PK_BACKENDS}" in
      # If the provided backend is valid
      *" $2 "*) 
        # Ask PackageKit to quietly close as soon as it can
        gdbus call --system --dest org.freedesktop.PackageKit --object-path /org/freedesktop/PackageKit --method org.freedesktop.PackageKit.SuggestDaemonQuit >/dev/null
        # Find the first instance of "DefaultBackend" in the configuration file and edit it
        sed -i .old "s/DefaultBackend=.*/DefaultBackend=$2/" ${PK_PREFIX}etc/PackageKit/PackageKit.conf
        # Sync the disks to make sure the configuration file is updated
        sync
        # Silently start PackageKit
        pkcon >/dev/null
        # Inform the user of success
        echo "PackageKit is now using the $2 backend"
        ;;
      # The default case is true if the provided backend name is not on the list of available backends
      *)
        # Notify the user of their mistake
        echo "The backend provided was not found, please check your entry"
        # Share usage advice with the user
        printUsage
        ;;
    esac
  fi
# End setBackend
}

# Explain to the user how to use this script, then exit
printUsage() {
  # Print the instructions to the user in an easily readable way
  echo "pk-setter is used to select the PackageKit backend"
  echo "usage: pk-setter status [prefix]"
  echo "       pk-setter list [prefix]"
  echo "       pk-setter set [backend] [prefix]"
  echo "note:  prefix is optional and defaults to \"/usr/local/\","
  echo "       and refers to the installation prefix of PackageKit"
  # Returns to the shell with error code
  exit 1
# End printUsage
}

# Notify the user of the current default back end, then exit
showStatus() {
  if [ "$1" == "status" ]; then
    # Load the variables from the configuration file; ignore errors, not a well-formed file 
    . ${PK_PREFIX}etc/PackageKit/PackageKit.conf 2>/dev/null
    # Notify the user of the current default back end by printing the DefaultBackend variable
    echo "PackageKit is currently using the $DefaultBackend back end"
  fi
# End showStatus
}

# Beginning of execution

# Make sure there is an appropriate number of arguments
if [ $# -eq 1 -o $# -eq 2 -o $# -eq 3 ]; then
  if [ "$1" == "list" -o "$1" == "set" -o "$1" == "status" ]; then
    # Determine if there is a user defined prefix, save the prefix for later
    setPrefix $*
    # List the current default back end if that is the action to do
    showStatus $*
    # If the user wants a list of backends then print it
    listBackends $*
    # Change the current backend if the user wants to 
    setBackend $*
    # Return to the shell with success
    exit 0
  fi
fi
# Let the user know how to use this script
printUsage

# End of execution