#!/usr/bin/env bash
# Copy the mirror onto a Rockbox device, then unmount it cleanly.
#
# The device is FAT32 with no journal, reached through the Apple firmware's
# disk mode because Rockbox's own mass storage is unreliable on an iFlash. An
# interrupted write is corruption that needs fsck.vfat from another machine, so
# this syncs and unmounts rather than leaving that to whoever pulls the cable.
#
# rsync --delete is pointed at a whole filesystem, so the checks below are the
# point of the script rather than decoration.

set -euo pipefail

usage() {
    cat >&2 <<'USAGE'
usage: sync-to-ipod.sh [options] <mirror> <destination>

  -n  dry run; show what would change and touch nothing
  -f  copy even if the FAT32 check finds unacceptable paths
  -S  skip submitting the Rockbox scrobbler log to Last.fm
  -U  leave the destination mounted afterwards

Submitting scrobbles needs LASTFM_API_KEY and LASTFM_API_SECRET; it is skipped
with a note when they are unset. Scrobbling is a write method and needs the
secret, unlike the read-only calls elsewhere in these projects.

The destination must be a mounted FAT filesystem. Reach it with the Apple
firmware's disk mode: Menu+Select to reboot, then immediately Select+Play.
USAGE
    exit 2
}

dry_run=false
force=false
unmount=true
scrobble=true
while getopts ":nfSUh" option; do
    case "$option" in
        n) dry_run=true ;;
        f) force=true ;;
        S) scrobble=false ;;
        U) unmount=false ;;
        *) usage ;;
    esac
done
shift $((OPTIND - 1))
[ $# -eq 2 ] || usage

mirror=${1%/}
destination=${2%/}
here=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)

die() {
    printf 'sync-to-ipod: %s\n' "$1" >&2
    exit 1
}

[ -d "$mirror" ] || die "mirror $mirror is not a directory"
[ -n "$(ls -A "$mirror")" ] || die "mirror $mirror is empty; refusing to mirror nothing"
[ -d "$destination" ] || die "destination $destination is not a directory"

# --delete makes every one of these load-bearing. A destination that is not its
# own mount point means the path is wrong, and emptying the wrong directory is
# not a mistake that announces itself.
case "$destination" in
    "" | "/" | "$HOME") die "refusing to sync onto $destination" ;;
esac
[ "$(readlink -f "$mirror")" != "$(readlink -f "$destination")" ] ||
    die "mirror and destination are the same directory"
mountpoint -q -- "$destination" || die "$destination is not a mount point"

filesystem=$(findmnt -no FSTYPE --target "$destination")
case "$filesystem" in
    vfat | exfat) ;;
    *)
        $force || die "$destination is $filesystem, not FAT; pass -f if that is deliberate"
        printf 'sync-to-ipod: destination is %s, not FAT\n' "$filesystem" >&2
        ;;
esac

if $force; then
    printf 'sync-to-ipod: skipping the FAT32 check\n' >&2
elif ! python3 "$here/check_fat32.py" "$mirror"; then
    die "the mirror holds paths FAT32 will not take; run music-mirror with --fat32-safe"
fi

# Before the copy, not after: the plays already happened, and if the transfer
# then fails there is no reason to have lost them too.
if $scrobble; then
    if [ -z "${LASTFM_API_KEY:-}" ] || [ -z "${LASTFM_API_SECRET:-}" ]; then
        printf 'sync-to-ipod: no Last.fm credentials, skipping the scrobbler log\n' >&2
    else
        scrobble_options=()
        $dry_run && scrobble_options+=(--dry-run)
        python3 "$here/submit_scrobbles.py" "${scrobble_options[@]}" "$destination" ||
            die "submitting scrobbles failed; nothing has been copied"
    fi
fi

# -rt rather than -a: owners, groups and permissions mean nothing on FAT, and
# asking for them produces a screenful of errors and a non-zero exit.
# --modify-window=2 because FAT stores mtimes to two-second resolution, without
# which every file looks changed and the whole library is copied every time.
# --delete removes tracks whose source has gone, which is the point. It would
# also remove everything on the device that the mirror does not contain -- and
# if the destination is the card root that means /.rockbox, the Rockbox install
# itself. Excluded paths are not deleted unless --delete-excluded is given,
# which it never is here.
options=(--recursive --times --delete --modify-window=2 --human-readable --info=progress2)
for owned in "/.rockbox" "/.scrobbler.log" "/.scrobbler.log.*" "/.playlist_control" \
    "/System Volume Information" "/.Spotlight-V100" "/.Trashes" "/.fseventsd"; do
    options+=(--exclude "$owned")
done
$dry_run && options+=(--dry-run --verbose)

printf 'sync-to-ipod: %s -> %s\n' "$mirror" "$destination" >&2
rsync "${options[@]}" "$mirror/" "$destination/"

if $dry_run; then
    printf 'sync-to-ipod: dry run, nothing was written\n' >&2
    exit 0
fi

sync
if $unmount; then
    device=$(findmnt -no SOURCE --target "$destination")
    printf 'sync-to-ipod: unmounting %s\n' "$device" >&2
    if command -v udisksctl >/dev/null 2>&1; then
        udisksctl unmount -b "$device"
    else
        umount -- "$destination"
    fi
    printf 'sync-to-ipod: safe to disconnect\n' >&2
else
    printf 'sync-to-ipod: still mounted; unmount before disconnecting\n' >&2
fi