#!/bin/bash

ENVNAME=$1
LAST_OCTET=$2

HASH=$(echo $ENVNAME | md5sum | head -c 6)

IP_OCTET_3=$(printf "%d" 0x$(echo $HASH | head -c 2))
IP_OCTET_4=$(printf "%d" 0x$(echo $HASH | tail -c 2))
IP_ADDR=10.0.$IP_OCTET_3.$IP_OCTET_4

# create root ns holder
touch .fleck-lock
mkdir -p .fleck-ns
flock -Fn .fleck-lock -c 'exec unshare -mrnU sh -c "echo $$ > .fleck-lock; rm .fleck-ns/netns/*; mount --bind .fleck-ns /run; exec sleep infinity"' &
sleep .1

ROOT_PID=$(cat .fleck-lock)

nsenter --preserve-credentials -U -m -n -t $ROOT_PID bash -x <<ROOT_NS
# do initial setup?
grep fleck-br <(ip link list) > /dev/null || (
    ip link set lo up
    ip link add name fleck-br type bridge
    ip link set dev fleck-br up
)

# set up namespace?
grep ^$ENVNAME$ <(ip netns list | awk '{print \$1}') > /dev/null || (
    ip netns add $ENVNAME > /dev/null
    ip link add $ENVNAME-root type veth peer name $ENVNAME-inner netns $ENVNAME
    ip link set $ENVNAME-root up
    ip link set $ENVNAME-root master fleck-br
    ip netns exec $ENVNAME ip link set up lo
    ip netns exec $ENVNAME ip link set up $ENVNAME-inner
    ip netns exec $ENVNAME ip addr add $IP_ADDR/16 dev $ENVNAME-inner
    ip netns exec $ENVNAME ip route add 224.0.0.0/4 dev $ENVNAME-inner
)

ROOT_NS

# give a shell
exec nsenter -w --preserve-credentials -U -m -n -t $ROOT_PID bash -i -c "DEBIAN_CHROOT=$ENVNAME ip netns exec $ENVNAME unshare --map-user=1024 $SHELL"