#!/bin/bash

exec_as() {
    local user="$1"
    shift

    if [ "$(whoami)" != "$user" ]; then
        exec sudo -u "$user" "$0" "$@"
    else
        cd || return
    fi
}

exec_as qemu "$@" || exit
PATH="./bin:${PATH}"

perror() {
    >&2 printf '\033[1;31mERROR:\033[0m \033[1m%s\033[0m\n' "$*"
}

public_help() {
    local name
    name="$(basename "$0")"
    cat << EOF
${name}: usage:
  ${name} active                      - (default behaviour) list active VMs
  ${name} start <VM name>             - start a VM
  ${name} watch <VM name>             - attach VM screen session
  ${name} list                        - list available VMs
  ${name} add <VM name> <template>    - add launch script based on template
  ${name} rm <VM name>                - delete launch script
  ${name} diskls                      - list available disk images
  ${name} diskadd <disk name> <size>  - create a disk image
  ${name} diskrm <disk name>          - delete disk image
  ${name} shell                       - start a shell as user qemu
  ${name} help                        - show this help
EOF
}

error_usage() {
    perror "Invalid usage"
    >&2 public_help
    return 1
}

public_start() {
    local vm_name="$1"
    shift

    screen -S "$vm_name" "$vm_name" "$@"
}

public_watch() {
    screen -dr "$1"
}

public_active() {
    screen -ls
}

public_list() {
    echo "Available machines:"
    ls --color=auto bin
}

diskpath() {
    printf 'images/%s.qcow2' "$1"
}

public_diskadd() {
    qemu-img create -f qcow2 "$(diskpath "$1")" "$2"
}

public_diskrm() {
    rm -vi -- "$(diskpath "$1")"
}

public_diskls() {
    echo "Available disks:"
    ls --color=auto images
}

public_add() {
    ln -vs "$2" "bin/${1}"
}

public_rm() {
    unlink "bin/${1}"
}

public_shell() {
    bash -i
}

function="$1"
shift

if [ -z "$function" ]; then
    public_active
elif declare -F | cut -d \  -f 3- | grep '^public_' | sed 's/^public_//' | grep -q "^${function}$"; then
    "public_${function}" "$@"
else
    error_usage
fi