#!/usr/bin/env bash
#
# Authors: danb, normalperson
#
# Useful for large-segment playlist manipulation.
#
# Opens the current playlist in an editor and lets the user remove/re-arrange
# (existing) tracks. Track addition is not supported (as there is no good
# interface to do so).

# avoid file name collisions
playlist_orig=`tempfile`
playlist_new=`tempfile`

while :; do
  case "$1" in
    --format)
      mpc_args="--format '$2'"; shift 2;;
    sort)
      sortpl=1; shift;;
    *) break;;
  esac
done

# store the playlist in two files
mpc $mpc_args playlist | tee "$playlist_orig" > "$playlist_new"

# let user edit the new playlist file (use vi by default)
if [ -n "$sortpl" ]; then
  sort -k 2 < "$playlist_orig" > "$playlist_new"
else
  ${EDITOR-"vi"} "$playlist_new"
fi

# insert requested songs into the list, keeping track of song positions
declare -a where_is_track
declare -a what_is_index
while read dest_index src_track
do

  # setup default values in lookup arrays, if applicable
  for i in $dest_index $src_track
  do
    if [ -z "${where_is_track[$i]}" ]
    then
      where_is_track[$i]=$i
    fi
    if [ -z "${what_is_index[$i]}" ]
    then
      what_is_index[$i]=$i
    fi
  done

  # alias the other 2 of {src,dest}_{index,track}
  src_index=${where_is_track[$src_track]}
  dest_track=${what_is_index[$dest_index]}

  # swap tracks, if necessary (avoid the mpc swap command for back compat.)
  if [ $src_index != $dest_index ]
  then

    # swap
    declare offset
    if [ $src_index -lt $dest_index ]
    then
      offset=-1
    else
      offset=1
    fi
    mpc move $src_index $dest_index
    mpc move $(($dest_index + $offset)) $src_index

    # update locations to reflect the swap
    where_is_track[$src_track]=$dest_index
    where_is_track[$dest_track]=$src_index
    what_is_index[$src_index]=$dest_track
    what_is_index[$dest_index]=$src_track

  fi

done < <(
  # parse the line numbers and track numbers from the new playlist
  awk '/^[#> ]/ { gsub(/[#)> ]/,"",$1); print NR, $1 }' < "$playlist_new"
)

# get the (inclusive) range of items to delete
min=$((`wc -l "$playlist_new" | (read n file; echo $n)` + 1))
max=`wc -l "$playlist_orig" | (read n file; echo $n)`

# remove deleted songs
if [ $min -le $max ]; then
  mpc del $min-$max
fi

# remove the tempfiles
rm "$playlist_orig" "$playlist_new"