#!/bin/bash -eu

function log_progress () {
  if declare -F setup_progress > /dev/null
  then
    setup_progress "create-backingfiles: $1"
    return
  fi
  echo "create-backingfiles: $1"
}

log_progress "starting"

CAM_SIZE="$1"
MUSIC_SIZE="$2"
# strip trailing slash that shell autocomplete might have added
BACKINGFILES_MOUNTPOINT="${3/%\//}"

log_progress "cam: $CAM_SIZE, music: $MUSIC_SIZE, mountpoint: $BACKINGFILES_MOUNTPOINT"

G_MASS_STORAGE_CONF_FILE_NAME=/etc/modprobe.d/g_mass_storage.conf

function first_partition_offset () {
  local filename="$1"
  local size_in_bytes
  local size_in_sectors
  local sector_size
  local partition_start_sector

  size_in_bytes=$(sfdisk -l -o Size -q --bytes "$1" | tail -1)
  size_in_sectors=$(sfdisk -l -o Sectors -q "$1" | tail -1)
  sector_size=$(( size_in_bytes / size_in_sectors ))
  partition_start_sector=$(sfdisk -l -o Start -q "$1" | tail -1)

  echo $(( partition_start_sector * sector_size ))
}

# Note that this uses powers-of-two rather than the powers-of-ten that are
# generally used to market storage.
function dehumanize () {
  echo $(($(echo "$1" | sed 's/GB/G/;s/MB/M/;s/KB/K/;s/G/*1024M/;s/M/*1024K/;s/K/*1024/')))
}

function is_percent() {
  echo "$1" | grep '%' > /dev/null
}

available_space () {
  freespace=$(df --output=avail --block-size=1K "$BACKINGFILES_MOUNTPOINT/" | tail -n 1)
  # leave 6 GB of free space for filesystem bookkeeping and snapshotting
  # (in kilobytes so 6M KB)
  # TODO: investigate whether this value can be smaller in general, or
  # when SMB access is not enabled.
  padding=$(dehumanize "6M")
  echo $((freespace-padding))
}

function calc_size () {
  local requestedsize="$1"
  local availablesize
  availablesize="$(available_space)"
  if [ "$availablesize" -lt 0 ]
  then
    echo "0"
    return
  fi
  if is_percent "$requestedsize"
  then
    local percent=${requestedsize//%/}
    requestedsize="$(( availablesize * percent / 100 ))"
  else
    requestedsize="$(( $(dehumanize $requestedsize) / 1024 ))"
  fi
  if [ "$requestedsize" -gt "$availablesize" ]
  then
    requestedsize="$availablesize"
  fi
  echo "$requestedsize"
}

function add_drive () {
  local name="$1"
  local label="$2"
  local size="$3"
  local filename="$4"

  log_progress "Allocating ${size}K for $filename..."
  fallocate -l "$size"K "$filename"
  echo "type=c" | sfdisk "$filename" > /dev/null

  local partition_offset
  partition_offset=$(first_partition_offset "$filename")

  loopdev=$(losetup -o "$partition_offset" -f --show "$filename")
  log_progress "Creating filesystem with label '$label'"
  mkfs.vfat "$loopdev" -F 32 -n "$label"
  losetup -d "$loopdev"

  local mountpoint=/mnt/"$name"

  if [ ! -e "$mountpoint" ]
  then
    mkdir "$mountpoint"
  fi
  sed -i "\@^$filename .*@d" /etc/fstab
  echo "$filename $mountpoint vfat utf8,noauto,users,umask=000,offset=$partition_offset 0 0" >> /etc/fstab
  log_progress "updated /etc/fstab for $mountpoint"
}

function create_default_entries () {
  mount /mnt/cam
  mkdir /mnt/cam/TeslaCam
  mkdir /mnt/cam/TeslaTrackMode
  touch /mnt/cam/.metadata_never_index
  umount /mnt/cam
  if [ -e /mnt/music ]
  then
    mount /mnt/music
    touch /mnt/music/.metadata_never_index
    umount /mnt/music
  fi
}

CAM_DISK_FILE_NAME="$BACKINGFILES_MOUNTPOINT/cam_disk.bin"
MUSIC_DISK_FILE_NAME="$BACKINGFILES_MOUNTPOINT/music_disk.bin"

# delete existing files, because fallocate doesn't shrink files, and
# because they interfere with the percentage-of-free-space calculation
if [ -t 0 ]
then
  read -r -p 'Delete snapshots and recreate recording and music drives? (yes/cancel)' answer
  case ${answer:0:1} in
    y|Y )
    ;;
    * )
      log_progress "aborting"
      exit
    ;;
  esac
fi
killall archiveloop || true
modprobe -r g_mass_storage
umount -d /mnt/cam || true
umount -d /mnt/music || true
umount -d /backingfiles/snapshots/snap*/mnt || true
rm -f "$CAM_DISK_FILE_NAME"
rm -f "$MUSIC_DISK_FILE_NAME"
rm -rf "$BACKINGFILES_MOUNTPOINT/snapshots"

CAM_DISK_SIZE="$(calc_size "$CAM_SIZE")"
MUSIC_DISK_SIZE="$(calc_size "$MUSIC_SIZE")"

add_drive "cam" "CAM" "$CAM_DISK_SIZE" "$CAM_DISK_FILE_NAME"
log_progress "created camera backing file"

REMAINING_SPACE="$(available_space)"

if [ "$CAM_SIZE" = "100%" ]
then
  MUSIC_DISK_SIZE=0
elif [ "$MUSIC_DISK_SIZE" -gt "$REMAINING_SPACE" ]
then
  MUSIC_DISK_SIZE="$REMAINING_SPACE"
fi

if [ "$REMAINING_SPACE" -ge 1024 ] && [ "$MUSIC_DISK_SIZE" -gt 0 ]
then
  add_drive "music" "MUSIC" "$MUSIC_DISK_SIZE" "$MUSIC_DISK_FILE_NAME"
  log_progress "created music backing file"
  echo "options g_mass_storage file=$MUSIC_DISK_FILE_NAME,$CAM_DISK_FILE_NAME removable=1,1 ro=0,0 stall=0 iSerialNumber=123456" > "$G_MASS_STORAGE_CONF_FILE_NAME"
else
  echo "options g_mass_storage file=$CAM_DISK_FILE_NAME removable=1 ro=0 stall=0 iSerialNumber=123456" > "$G_MASS_STORAGE_CONF_FILE_NAME"
fi

create_default_entries
log_progress "done"