#! /bin/bash
# /usr/bin/pacman2pacman-get
#
# Version 1.5.1
#
# Copyright (C) 2014 Joseph Graham <joseph@t67.eu>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

shopt -s extglob

torrent_folder='/srv/pacman2pacman/torrents'

pkg_cache_location='/var/cache/pacman/pkg'

# Pacman2pacman should be called like this from /etc/pacman.conf:
# XferCommand = /usr/bin/pacman2pacman-get %u %o

# Check that the args are not empty.
[[ -z ${1} ]] && { echo "The first argument should be the download url." ; exit 1 ; }
[[ -z ${2} ]] && { echo "The second argument should be the local filename, plus a “.part” extension." ; exit 1 ; }

url="${1}"  # The download url.
filename="${2}"  # This is where the downloaded file needs to be saved
                 # or hardlinked

# Check if transmission daemon is running.
if ! systemctl show --property='ActiveState' transmission | grep -q 'ActiveState=active'
then
    echo 'Error: The transmission daemon is not running.'
    exit 1
fi

cd "${torrent_folder}"

# Find the name of the package that will be displayed
pname="${url##*/}"
pname="${pname%%-[[:digit:]]*}"

# Find out if it's a dbfile
if [[ "${url}" == *'.db' ]] || [[ "${url}" == *'.db.sig' ]]
then
    dbfile=1
else
    dbfile=0
fi

# Check for a .torrent.

# We will cycle through the mirrors in the mirrorlist, trying to get
# the torrent file for this package. If it fails we keep trying more
# mirrors until we get a 404 or a success, because only a 404
# indicates that the .torrent does not exist.

# If it's a .db file then we don't even check for a .torrent
if (( dbfile ))
then
    response='no_torrent'

else
    while read mirror
    do
        # Remove the `Server = ' part, whether it has spaces or not
        mirror="${mirror##Server?( )=?( )}"

        torrent_url="${mirror%%\$*}torrents/${url##*/}.torrent"
        
        err=$( curl -O -f -L -s -A 'Pacman2pacman' "${torrent_url}" )

        if [[ "${?}" == 0 ]]
        then
            response='found_torrent'
            break

        elif [[ "${err}" == *'404'* ]]
        then
            response='no_torrent'
            break
        fi
    done < <(grep 'Server \?= \?' "/etc/pacman.d/mirrorlist")
fi

# If there's a .torrent we download the package with transmission
# otherwize we just download it by http.
if [[ "${response}" == 'found_torrent' ]]
then
    cd "${pkg_cache_location}"

    # Re-write the webseeds in the torrent to make it use the user's
    # own mirror. We can just use the ${url} var.

    # We need to find out the length of the ${url} var.
    len="${#url}"

    sed "s#url-listl[[:digit:]]\+.\+.pkg.tar.xz#url-listl${len}:${url}#" < "${torrent_folder}/${url##*/}.torrent" > "${torrent_folder}/${url##*/}.torrent.modified"

    mv "${torrent_folder}/${url##*/}.torrent.modified" "${torrent_folder}/${url##*/}.torrent"

    # Add the torrent to transmission
    transmission-remote -a "${torrent_folder}/${url##*/}.torrent" -w "${pkg_cache_location}" &>/dev/null

    # The torrent is now downloading. To get info about the torrent in
    # order to display a progress bar we need to know it's id.

    # Find out the id of the torrent
    id=$(transmission-remote -l | grep "${url##*/}")
    id="${id## }"
    id="${id## }"
    id="${id## }"
    id="${id## }"
    id="${id## }"
    id="${id## }"
    id="${id## }"
    id="${id## }"
    id="${id## }"
    id="${id## }"
    id="${id## }"  # Once should be enough but somehow it's not so I do
                   # it loads of times.
    id="${id%% *}"

    # If there is an error there will be an asterix displayed on the
    # end of the id. We must remove it.
    id="${id%\*}"

    if ! [[ ${id} =~ [[:digit:]] ]]
    then
        echo 'Error.'
        exit 1
    fi

    # Display a progress bar until it's finished and then hardlink it to
    # the right place.
    progress='0.0%'

    echo -n "Pacman2pacman p2p download: ${pname}: ${progress}"

    count=0

    declare -a last_webseed_check=(0 'working')

    webseed_check_after='100'

    until [[ "${progress}" == '100%' ]]
    do
        progress=$(transmission-remote -t "${id}" -i | grep 'Percent Done:')
        progress="${progress##* }"  # Remove stuff we don't want

        # If we're still at 0.0% after ${webseed_check_after} attempts
        # then we check if the webseed is actually valid.
        if (( count >= webseed_check_after )) && [[ "${progress}" == '0.0%' ]]
        then
            # Find out if we already checked recently.
            if (( (last_webseed_check[0] + (webseed_check_after / 2)) > count ))
            then
                if [[ last_webseed_check[1] == 'broken' ]]
                then
                    # Just set the message without checking.
                    progress='0.0% Warning: Webseed dead...'
                else
                    # We don't need to do anything
                    true
                fi
            else
                if ! $(curl -IL "${url}" | grep '200 OK' &>/dev/null)
                then
                    # The webseed seems to be invalid so we print an error
                    # message.

                    progress='0.0% Warning: Webseed dead...' # This
                                                             # most
                                                             # likely
                                                             # means
                                                             # the
                                                             # user
                                                             # needs
                                                             # to run
                                                             # pacman
                                                             # -Sy, or
                                                             # that
                                                             # their
                                                             # internet
                                                             # is
                                                             # down.

                    # If there are no peers we remove the torrent from
                    # transmission, print an error message and exit.
                    if (( $(transmission-remote -t "${id}" -pi | wc -l) < 2 ))
                        transmission-remote -t "${id}" -r
                        echo "Webseed dead and no peers, removing torrent from transmission and exiting."
                        exit 1
                    fi

                    last_webseed_check[0]="${count}"
                    last_webseed_check[1]="broken"
                else
                    # The webseed is valid so we just record that we checked
                    last_webseed_check[0]="${count}"
                    last_webseed_check[1]="working"
                fi
            fi
        fi

        printf "\rPacman2pacman p2p download: %s: %s   " "${pname}" "${progress}"

        sleep 0.7

        (( count ++ ))
    done

    echo

    err_count=0
    until mv -f "${pkg_cache_location}/${url##*/}" "${filename}" 2>/dev/null
    do
        if (( err_count > 50 ))
        then
            echo "error moving \"${pkg_cache_location}/${url##*/}\""
            exit 1
        fi

        sleep 0.1

        (( ++ err_count ))
    done

else
    cd "${pkg_cache_location}"
    # There's no .torrent so we download it by just HTTP.

    # We must do some complicated stuff to customise the progress
    # meter how we want it, to make it consistent with the progress
    # bar when we download stuff with transmission.

    mod_time=$(stat -c %Y "/srv/pacman2pacman/dbcache/${filename##*/}" 2>/dev/null)

    progress='0.0%'

    echo -n "Pacman2pacman http download: ${pname}: ${progress}"

    # The first loop gets rid of all the backspace and `#'es and
    # stuff. The second loop isolates the percent done number.
    {
        # For dbs we check if they are modified
        if (( dbfile ))
        then
            if [[ -f "/srv/pacman2pacman/dbcache/${filename##*/}" ]]
            then
                curl -# -f -L -z "/srv/pacman2pacman/dbcache/${filename##*/}" -o "/srv/pacman2pacman/dbcache/${filename##*/}" -A 'Pacman2pacman' "${url}" 2>&1
            else
                curl -# -f -L -o "/srv/pacman2pacman/dbcache/${filename##*/}" -A 'Pacman2pacman' "${url}" 2>&1
            fi
        else
            curl -# -f -L -o "${filename}" -A 'Pacman2pacman' "${url}" 2>&1
        fi
    } |
    while read -N 1 char
    do
        [[ "${char}" =~ [[:digit:].%\ ] ]] && echo -n "${char}"
    done |
    {
        while read -d '%' word
        do
            progress="${word}%"

            # There's a crazy bug that causes it to display 100% at the
            # start of the download. This should fix it.
            [[ "${progress}" == '100.0%' ]] && continue

            printf "\rPacman2pacman http download: %s: %s   " "${pname}" "${progress}"
        done

        # It's the end of the download so we can now display 100%
        if [[ "${progress}" == '100.0%' ]]
        then
            progress='100%'
            printf "\rPacman2pacman http download: %s: %s   " "${pname}" "${progress}"
        fi
    }

    # What was the result of the download?
    if (( dbfile ))
    then
        # If we fail to stat it that means it doesn't exist so the
        # download failed.
        if ! new_mod_time=$(stat -c %Y "/srv/pacman2pacman/dbcache/${filename##*/}" 2>/dev/null)
        then
            progress='failed'
            printf "\rPacman2pacman http download: %s: %s   " "${pname}" "${progress}"

        # If the file was not modified we display such
        elif [[ "${new_mod_time}" == "${mod_time}" ]]
        then
            progress='file not modified'
            printf "\rPacman2pacman http download: %s: %s   " "${pname}" "${progress}"
        fi
    else
        # It's not a dbfile. Just check the output file exists.
        if ! [[ -f "${filename}" ]]
        then
            progress='failed'
            printf "\rPacman2pacman http download: %s: %s   " "${pname}" "${progress}"
        fi
    fi
 
    echo

    if (( dbfile )) && [[ -f "/srv/pacman2pacman/dbcache/${filename##*/}" ]]
    then
        cp "/srv/pacman2pacman/dbcache/${filename##*/}" "${filename}" 2>/dev/null
    fi

    [[ -f "${filename}" ]] || exit 1

fi

exit