#!/bin/bash

mkdir -p .join/

if ! [[ -z "$TMUX" ]]; then
    printf >&2 'Already in tmux, unset TMUX to force nesting\n'
    exit 1
fi

name="$1"
if [[ $name == "" ]]; then
    printf >&2 'Usage: %s NAME\n' "$0"
    exit 1
fi

set -o noclobber

# duplicate stderr to fd 3
exec 3>&2
# kill stderr to hide noclobber errors
exec 2>/dev/null

function sessionname {
    if (($# != 2)); then
        printf >&3 'sessionname requires exactly two arguments\n'
        exit 1
    fi
    if [[ "$1" < "$2" ]]; then
        printf '%s\n' "$1-$2"
    else
        printf '%s\n' "$2-$1"
    fi
}

if printf '%s\n' "$name" > .join/join1; then
    # we're the first
    name1=$name
    trap 'rm -f .join/join1' EXIT
    # wait for second
    printf 'Waiting for second client...\n'
    while ! [[ -f .join/join2 ]]; do
        sleep 1
    done
    read -r name2 < .join/join2
    trap "echo false >| .join/$name1-$name2; rm -f .join/join1" EXIT
    read -p "Do you want to collaborate with $name2? [Y/n] " -r response 2>&3
    if [[ "$response" =~ ^[Nn] ]]; then
        echo false >| .join/"$name1-$name2"
        exit 1
    else
        # set up session
        if ! tmux has-session -t "$(sessionname "$name1" "$name2")" &> /dev/null; then
            tmux new-session -s "$(sessionname "$name1" "$name2")" -d
            tmux set-hook -t "$(sessionname "$name1" "$name2")" client-detached "run 'tmux detach-client -s $(sessionname "$name1" "$name2"); true'"
        fi
        echo true >| .join/"$name1-$name2"
    fi
    rm -f .join/join1 .join/join2
    # ready
else
    read -r name1 < .join/join1
    read -p "Do you want to collaborate with $name1? [Y/n] " -r response 2>&3
    if [[ "$response" =~ ^[Nn] ]]; then
        exit 1
    fi
    if printf '%s\n' "$name" > .join/join2; then
        # we're the second
        trap 'rm -f .join/join2' EXIT
        read -r name1 < .join/join1
        name2=$name
        if [[ "$name1" == "$name2" ]]; then
            printf >&3 'same client twice not allowed, exiting\n'
            exit 1
        fi
        # wait for first to acknowledge collaboration
        while ! [[ -f .join/"$name1-$name2" ]]; do
            if ! read -r name1_ < .join/join1 || ! [[ "$name1_" == "$name1" ]]; then
                printf >&3 '%s has aborted collaboration.\n' "$name1"
                exit 1
            fi
            sleep 1
        done
        read -r ack < ".join/$name1-$name2"
        rm -f ".join/$name1-$name2"
        if [[ $ack != true ]]; then
            printf >&3 '%s does not want to collaborate with you\n' "$name1"
            exit 1
        fi
    else
        # we're the third one, nope
        printf >&3 'two clients already connected, exiting\n'
        exit 1
    fi
fi
if [[ "$name1" == "$name2" ]]; then
    printf >&3 'same client twice not allowed, exiting\n'
    exit 1
fi
(
    while tmux has-session -t "$(sessionname "$name1" "$name2")"; do
        sleep 5
        [[ -f .join/"$name1-$name2" ]] && rm -f ".join/$name1-$name2"
        if (($(tmux list-clients -t "$(sessionname "$name1" "$name2")" | wc -l)!=2)); then
            tmux detach-client -s "$(sessionname "$name1" "$name2")"
            break
        fi
    done
) &
exec tmux attach -t "$(sessionname "$name1" "$name2")"