#!/bin/bash

# Log everthing to stdout.
# Use qrexc output only to communicate success/failure
exec {qrexec_output}>&1
exec 1>&2

set -eu -o pipefail

tmp=

error() {
    printf "Error: $1\n" "${@:2}"
    exit
}

exit_ok() {
    printf "Ok: $2\n" "${@:3}"
    printf "$1\n" >&$qrexec_output
    exit
}

cleanup() {
    if [ -n "$tmp" ]; then
        rm -rf "$tmp"
    fi
}

check_apt_version() {
    local pkg="$1"
    local fixed_version="$2"
    if [ -z "$fixed_version" ] || [ -z "$pkg" ]; then
        error "Bug: Invalid argument!"
    fi

    installed_version="$(dpkg -s $pkg | grep '^Version: ' | cut -d ' ' -f 2)"
    if [ -z "$installed_version" ]; then
        error "Failed to get apt version."
    fi

    rc=0
    dpkg --compare-versions "$installed_version" ge "$fixed_version" || rc=$?

    if [ "$rc" -gt 1 ]; then
        error "Bug: Failed to compare versions!"
    fi

    return $rc
}

main() {
    if [ ! -e /etc/debian_version ]; then
        exit_ok 'changed=no' 'Not a Debian.'
    fi

    trap cleanup EXIT
    tmp="$(mktemp -d --tmpdir)"

    codename="$(cat /etc/debian_version)"
    case "$codename" in
        */sid|10.*|kali-*)
            # We will treat testing as sid here. This hopefully won't break
            # anything ...
            codename="sid"
            pkg="libapt-pkg5.0"
            fixed_version="1.8.0~alpha3.1"
            ;;
        8.*)
            codename="jessie"
            pkg="libapt-pkg4.12"
            fixed_version="1.0.9.8.5"
            ;;
        9.*)
            codename="stretch"
            pkg="libapt-pkg5.0"
            fixed_version="1.4.9"
            ;;
        *)
            error 'Error: Could not determine Debian release!'
    esac

    if check_apt_version "$pkg" "$fixed_version"; then
        exit_ok 'changed=no' 'Nothing to do, apt already fixed.'
    fi

    : > "$tmp/sources.list"
    mkdir "$tmp/sources.list.d"

    # Make sure that any old (maybe bogus) list is removed.
    apt-get \
        -o "Acquire::http::AllowRedirect=false" \
        -o "Dir::Etc::SourceList=$tmp/sources.list" \
        -o "Dir::Etc::SourceParts=$tmp/sources.list.d" \
        --list-cleanup \
        update

    printf 'deb http://cdn-fastly.deb.debian.org/debian %s main\n' "$codename" > "$tmp/sources.list"
    if [ "$codename" != "sid" ]; then
        printf 'deb http://cdn-fastly.deb.debian.org/debian-security %s/updates main\n' "$codename" >> "$tmp/sources.list"
    fi

    # Don't fetch Translation and Contents file. We don't need them and we will
    # throw them away later anyway.
    apt-get \
        -o "Acquire::http::AllowRedirect=false" \
        -o "Acquire::Languages=none" \
        -o "Acquire::IndexTargets::deb::Contents-deb::DefaultEnabled=false" \
        -o "Dir::Etc::SourceList=$tmp/sources.list" \
        -o "Dir::Etc::SourceParts=$tmp/sources.list.d" \
        update

    apt-get \
        -o "Acquire::http::AllowRedirect=false" \
        -o "Dir::Etc::SourceList=$tmp/sources.list" \
        -o "Dir::Etc::SourceParts=$tmp/sources.list.d" \
        --no-remove \
        --only-upgrade \
        -y \
        install "$pkg"

    if ! check_apt_version "$pkg" "$fixed_version"; then
        error 'apt version is still not fixed!'
    fi

    # Run update again to restore normal package sources.
    apt-get update

    exit_ok 'changed=yes' "Done."
}

main