#!/bin/bash

# All credit for this file goes to @mandreyel, creator of cratetorrent.
# Excellent test setup that I've stolen.
#
# This file sets up a test environment with specific details supplied as command
# line arguments.
#
# It creates a metainfo of the given torrent file or directory and starts
# seeding it in the given Transmission container.

set -e


function print_help {
    echo -e "
This makes the seed container start seeding the given file (generating its necessary metainfo).
The seed container must be running.
USAGE: $1 --path <path> [--seed <seed>] 
OPTIONS:
    -n|--name       The name of the torrent (currently the name of the file).
    -p|--path       The path of the torrent file or directory to seed. This will
                    be copied into the container's downloads complete folder.
    --seed          The Transmission seed container's name. Must be running.
                    Defaults to 'transmission'.
    -h|--help       Print this help message.
    "
}

for arg in "$@"; do
    case "${arg}" in
        -n|--name)
            torrent_name=$2
        ;;
        -p|--path)
            path=$2
        ;;
        --seed)
            seed_container=$2
        ;;
        --h|--help)
            print_help
            exit 0
        ;;
    esac
    shift
done

if [ -z "${torrent_name}" ]; then
    echo "Error: --name must be set"
    print_help
    exit 1
fi

if [ -z "${path}" ]; then
    echo "Error: --path must be set"
    print_help
    exit 1
fi

if [ -z "${seed_container}" ]; then
    echo "Error: --seed must be set"
    print_help
    exit 1
fi


################################################################################
# 1. Verify seed
################################################################################

# where the necessary seed directories exist
assets_dir="$(pwd)/assets"
if [ ! -d "${assets_dir}" ]; then
    echo "Error: assets directory ${assets_dir} does not exist"
    exit 2
fi

# check that the container's directories exist
tr_seed_dir="${assets_dir}/${seed_container}"
if [ ! -d "${tr_seed_dir}" ]; then
    echo "Error: seed directory ${tr_seed_dir} does not exist"
    exit 3
fi
tr_config_dir="${tr_seed_dir}/config"
tr_downloads_dir="${tr_seed_dir}/downloads"
tr_watch_dir="${tr_seed_dir}/watch"
for subdir in {"${tr_config_dir}","${tr_downloads_dir}","${tr_watch_dir}"}; do
    if [ ! -d "${subdir}" ]; then
        echo "Error: seed subdirectory ${subdir} does not exist"
        exit 4
    fi
done

# check if the seed is running: if not, abort
if ! docker inspect --format '{{.State.Running}}' "${seed_container}" &> /dev/null
then
    echo "Error: Transmission seed container ${seed_container} is not running"
    exit 5
fi

################################################################################
# 2. Verify file to seed
################################################################################

if [ ! -f "${path}" ] && [ ! -d "${path}" ]; then
    echo "Error: torrent file does not exist at ${path}"
    exit 6
fi

################################################################################
# 3. Create torrent
################################################################################

# The source to be seeded must be inside the container. For this reason, if it
# is not already there, we copy it in the torrent downloads complete folder.
# This should be a cheap even for large files as we're not actually modifying
# the source so linux should do a copy-on-write here.
torrent_path="${tr_downloads_dir}/complete/${torrent_name}"
if [ "${path}" != "${torrent_path}" ]; then
    echo "Copying torrent from source ${path} to seed dir at ${torrent_path}"
    cp -r "${path}" "${torrent_path}"
fi

tr_metainfo_basepath="${tr_watch_dir}/${torrent_name}"
tr_metainfo_path="${tr_metainfo_basepath}.torrent"
assets_metainfo_path="${assets_dir}/${torrent_name}.torrent"

# The metainfo for the torrent may already exist if another seed is already
# seeding it. If it doesn't, create it inside the seed container and
# copy the metainfo into the assets folder so that it is available for others.
# If it exists, we just need to copy the existing metainfo inside the
# container.
if [ -f "${assets_metainfo_path}" ]; then
    # the metainfo in assets is just a symlink so we need to follow it
    cp --dereference "${assets_metainfo_path}" "${tr_metainfo_path}"

    # wait for Transmission to pick up the file
    sleep 5
else 
    # NOTE: The file is not created with the `.torrent` suffix on purpose! Since the
    # Transmission container can only be run as root, the metainfo file is also
    # created as root.  However, this would cause a permission denied error for the
    # Transmission container itself, as it is running as the specified user/group.
    # By not specifying the `.torrent` suffix, Transmission won't pick it up, so we
    # get a chance to change its permissions before adding the suffix. 
    #
    # It may be possible to solve this by spawning a subshell with a different EUID
    # and execute the `transmission-create` command there, but currently it is not
    # clear how to do this.

    echo "Creating torrent metainfo file"
    docker exec "${seed_container}" transmission-create \
      -o "/watch/${torrent_name}" \
      "/downloads/complete/${torrent_name}"

    # change ownership of the metainfo file to the same user whose `UID` and `GID`
    # were given to the seed container
    #
    # TODO: make this work without sudo
    echo "Changing metainfo owner from root to $USER"
    sudo chown $USER:$USER "${tr_metainfo_basepath}"

    # rename the torrent file to have the `.torrent` suffix, which will make the
    # Transmission daemon automatically start seeding the torrent
    echo "Adding .torrent suffix to metainfo filename"
    mv "${tr_metainfo_basepath}" "${tr_metainfo_path}"

    # wait for Transmission to pick up the file
    sleep 5

    # we need to add the `.added` suffix to our path as that's what Transmission does after
    # picking up a new metainfo file
    tr_metainfo_path="${tr_metainfo_path}.added"
    # sanity check
    if [ ! -f "${tr_metainfo_path}" ]; then
        echo "Error: could not find metainfo ${tr_metainfo_path} after starting torrent"
        exit 7
    fi

    # link metainfo file in the transmission watch directory to the root of the
    # assets dir for use by other scrips
    echo "Linking metainfo to assets directory root"
    ln -s "${tr_metainfo_path}" ${assets_metainfo_path}
fi

echo "Done!"
echo "Torrent ${torrent_name} is seeded by container ${seed_container}"