#! /bin/bash

set -e
: ${JBDIR=/mnt/jb}

case $# in
  3) ;;
  *) echo >&2 "Usage: $0 OFFSET SOURCEDIR TARGETDIR"; exit 1 ;;
esac

offset=$1 sourcedir=$2 targetdir=$3
mkdir "$targetdir"
tmp="$targetdir"/_tmp; mkdir "$tmp"
trap 'rm -rf "$targetdir"' EXIT INT TERM

lens=""
for i in "$sourcedir"/*.flac; do
  base=${i##*/}
  metaflac --export-tags-to="$tmp/${base%.flac}.tags" "$i"
  len=$(metaflac --show-total-samples "$i")
  lens="${lens:+$lens }$len"
done

{
  if ((offset < 0)); then
    $JBDIR/bin/cat-prefix $((4 * -offset)) </dev/zero
  fi
  for i in "$sourcedir"/*.flac; do
    flac -d -s -o- --force-raw-format --sign=signed --endian=little "$i"
  done
  if ((offset > 0)); then
    $JBDIR/bin/cat-prefix $((4 * offset)) </dev/zero
  fi
} | {
  if ((offset > 0)); then
    $JBDIR/bin/cat-prefix $((4 * offset)) >/dev/null
  fi
  set -- $lens
  for i in "$sourcedir"/*.flac; do
    base=${i##*/}
    len=$1; shift
    $JBDIR/bin/cat-prefix $((4 * len)) >"$tmp"/"${base%.flac}.pcm"
    flac --force-raw-format --sign=signed --endian=little --channels=2 \
      --bps=16 --sample-rate=44100 --best -o "$targetdir"/"$base" \
      "$tmp"/"${base%.flac}.pcm"
    metaflac --remove-all-tags \
      --import-tags-from="$tmp"/"${base%.flac}.tags" \
      "$targetdir"/"$base"
  done
  if ((offset < 0)); then
    $JBDIR/bin/cat-prefix $((4 * -offset)) >/dev/null
  fi
}

for i in "$sourcedir"/* "$sourcedir"/.[!.]*; do
  if [ ! -e "$i" ]; then continue; fi
  case "$i" in
    *.flac) ;;
    *) cp -r "$i" "$targetdir"/ ;;
  esac
done

rm -rf "$tmp"
trap '' EXIT INT TERM