#!/bin/bash

function osxiso() {

  local app # path for "Install OS X <version>.app"

  function usage() {
    cat <<EOF

    Create a bootable ISO of OS X / macOS, from the installation app file.

    Usage:

      $ ${0##*/} <Sierra|"El Capitan"|Yosemite|Mavericks>

EOF
    exit 1
  }

  function build() {
    local temp="$PWD/temp"
    local dist="$PWD/dist"
    local iso="$dist/$1.iso"
    local app_mount="/Volumes/install_app"
    local build_mount="/Volumes/install_build"
    local base_mount="/Volumes/OS X Base System"

    function detach_mounts() {
      echo "Attempting to detach mounts"

      # Unmount the installer image
      [[ ! -d  "$app_mount" ]] || hdiutil detach "$app_mount"

      # Unmount the sparse bundle
      [[ ! -d  "$base_mount" ]] || hdiutil detach "$base_mount"
    }

    function cleanup() {
      detach_mounts

      # Remove temp directory
      rm -rf "$temp"
    }

    function abort() {
      printf "\nCommand returned with error, aborting ...\n\n"
      exit 2
    }

    trap cleanup EXIT
    trap abort ERR

    # Attempt cleanup of any previous attempts
    cleanup

    # Prepare to do work
    mkdir -p "$temp"
    mkdir -p "$dist"

    # Mount the installer image
    hdiutil attach "$app/Contents/SharedSupport/InstallESD.dmg" -noverify -nobrowse -mountpoint "$app_mount"

    # Create a blank ISO of 7316MB with a Single Partition
    hdiutil create -o "$temp/$1.cdr" -size 7316m -layout SPUD -fs HFS+J

    # Mount the blank ISO
    hdiutil attach "$temp/$1.cdr.dmg" -noverify -nobrowse -mountpoint "$build_mount"

    # Restore the Base System into the blank ISO
    asr restore -source "$app_mount/BaseSystem.dmg" -target "$build_mount" -noprompt -noverify -erase

    # Remove Package link and replace with actual files
    rm "$base_mount/System/Installation/Packages"
    cp -rp "$app_mount/Packages" "$base_mount/System/Installation/"

    # Copy "$1" installer dependencies
    cp -rp "$app_mount/BaseSystem.chunklist" "$base_mount/BaseSystem.chunklist"
    cp -rp "$app_mount/BaseSystem.dmg" "$base_mount/BaseSystem.dmg"

    # Detach mounts
    detach_mounts

    # Convert the sparse bundle to ISO/CD master
    hdiutil convert "$temp/$1.cdr.dmg" -format UDTO -o "$temp/$1.iso"

    # Rename the ISO and move it to the distribution "dist" dir
    mv "$temp/$1.iso.cdr" "$iso"

    cleanup

    printf "\n========== FINISHED ==========\n\n"
    printf "ISO is located at '%s'\n\n" "$iso"
  }

  # Verify OS X Version
  [[ $# -ne 0 ]] || usage
  local versions=(
    Yosemite
    Mavericks
    "El Capitan"
    Sierra
  )
  for version in "${versions[@]}"; do
    if [[ "$1" = "$version" ]]; then
      if [[ "$1" = "Sierra" ]]; then
      	app="/Applications/Install macOS $1.app"
      else
      	app="/Applications/Install OS X $1.app"
      fi

      if [[ ! -e "$app" ]]; then
        cat <<EOF

  Missing: $app

  * You can install it with the App Store

EOF
        exit 1
      fi

      # Do Work
      build "$1"
      exit $?
    fi
  done

  # Invalid version provided
  usage
}

## Export or run
if [[ ${BASH_SOURCE[0]} != $0 ]]; then
  export -f osxiso
else
  osxiso "$@"
fi