#!/usr/bin/env bash

# Function to re-exec the script as another user via sudo (only if needed)
exec_as() {
    local user
    user="$1"
    shift

    if [ "$(whoami)" != "$user" ]; then
        exec sudo -E -H -u "$user" -- "$0" "$@"
    fi
}

# Exec the script as qemu
exec_as qemu "$@"

# Environment
PATH="${HOME}/launchers:${HOME}/bin:${PATH}"
EDITOR="${EDITOR:-nvim}"
export QEMUSH_NAME

# Aliases
ls='ls --color=auto'

# Set a restrictive umask to make sure qemu user files are private
umask 027

# Function to print a colored error
perror() {
    >&2 printf '\033[1;31mKO:\033[0m \033[1m%s\033[0m\n' "$*"
}

# Function to show the usage
public_help() {
    local name
    name=$(basename "$0")

    exec cat << EOF
${name}: usage:
  ${name} running                          - (default behaviour) list running VMs
  ${name} start <VM name>                  - start a VM
  ${name} attach <VM name>                 - attach to the VM monitor socket
  ${name} ls                               - list available VMs
  ${name} edit <VM name>                   - edit VM launching script
  ${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
  ${name} add <path to script> [<VM name>] - add a launching script
  ${name} do <command>                     - run shell input as user qemu
EOF
}

# Function to throw an invalid usage error (skill issue)
error_usage() {
    perror "Invalid usage"
    >&2 public_help
    return 1
}

# Function to start a virtual machine
public_start() {
    QEMUSH_NAME="$1"

    set -- "$@" \
        -monitor "unix:$(pathof socket),server,nowait" \
        -daemonize
    if ! "$@"; then
        perror "error launching virtual machine \"${QEMUSH_NAME}\""
        return 2
    fi
}

# Attach to a running virtual machine output, the latest opened if no
# argument is provided
public_attach() {
    QEMUSH_NAME="$1"
    shift

    exec socat -,rawer,escape=15 "UNIX-CONNECT:$(pathof socket)"
}

# List running virtual machines
public_running() {
    cd || return
    echo "Running machines:"
    set -- $ls -t sockets/monitors "$@"
    exec "$@"
}

# List available virtual machines entrypoints
public_ls() {
    cd || return
    echo "Available machines:"
    set -- $ls launchers "$@"
    exec "$@"
}

# Create a copy-on-write disk for a virtual machine
public_diskadd() {
    QEMUSH_NAME="$1"
    shift
    exec qemu-img create -f qcow2 "$(pathof disk)" "$1"
}

# Delete a disk
public_diskrm() {
    for disk in "$@"; do
        QEMUSH_NAME="$disk"
        rm -vi -- "$(pathof disk)"
    done
}

# List available disks
public_diskls() {
    cd || return
    echo "Available disks:"
    set -- $ls disks "$@"
    exec "$@"
}

# Edit a virtual machine entrypoint with a text editor
public_edit() {
    cd || return
    local file="launchers/${1}"

    "$EDITOR" "$file"
    [ -f "$file" ] && exec chmod u+x "$file"
}

# Delete a virtual machine entrypoint
public_rm() {
    cd ~/launchers || return
    exec rm -vi -- "$@"
}

# Invoke bash as qemu user in its home directory
public_shell() {
    cd || return
    set -- bash -i "$@"
    exec "$@"
}

# Output the content of an entrypoint, with coloration if on a virtual
# terminal
public_cat() {
    cd ~/launchers || return
    cat -- "$@"
}

# Copy a file in entrypoints folder
public_add() {
    trap return EXIT
    set -e

    local name
    if [ -n "$2" ]; then
        name="$2"
    else
        name=$(basename "$1")
    fi
    name="${HOME}/launchers/${name}"

    cp -vi -- "$1" "$name"
    chmod 740 "$name"

    set +e
    trap - EXIT
}

# Run shell commands as qemu
public_do() {
    exec sh -c "$*"
}

# Retrieve user requested function
function="$1"
shift

# Defauts to `active` if no function is supplied; else checks for a public
# function named after the argument; else fails
if [ -z "$function" ]; then
    public_running
elif declare -F | cut -d \  -f 3- | grep '^public_' | sed 's/^public_//' | grep -q "^${function}$"; then
    "public_${function}" "$@"
else
    error_usage
fi