#!/usr/bin/env bash
set -euo pipefail

# Installs Docker Engine + Docker Compose plugin on Ubuntu/Debian or RHEL-like (CentOS/Rocky/Alma).
# Adds a user to the "docker" group (so they can run docker without sudo).
#
# Usage:
#   sudo ./install-docker.sh
#   sudo ./install-docker.sh --user username
#   sudo ./install-docker.sh --user username --no-docker-group
#
# Notes:
# - After adding a user to docker group, they must re-login (or run: newgrp docker).

TARGET_USER=""
ADD_TO_DOCKER_GROUP="1"

usage() {
  cat <<'EOF'
Usage:
  install-docker.sh [--user <username>] [--no-docker-group]

Options:
  --user <username>       Add this user to docker group (default: current sudo user if set)
  --no-docker-group       Do not add any user to docker group
  -h, --help              Show help
EOF
}

while [[ $# -gt 0 ]]; do
  case "$1" in
    --user)
      [[ $# -ge 2 ]] || { echo "Missing value for --user" >&2; usage; exit 2; }
      TARGET_USER="$2"
      shift 2
      ;;
    --no-docker-group)
      ADD_TO_DOCKER_GROUP="0"
      shift
      ;;
    -h|--help)
      usage
      exit 0
      ;;
    *)
      echo "Unknown argument: $1" >&2
      usage
      exit 2
      ;;
  esac
done

if [[ "${EUID}" -ne 0 ]]; then
  echo "Run as root (sudo)." >&2
  exit 1
fi

# Default user: the sudo invoker (if any), else empty
if [[ -z "${TARGET_USER}" && -n "${SUDO_USER:-}" && "${SUDO_USER}" != "root" ]]; then
  TARGET_USER="${SUDO_USER}"
fi

if command -v docker >/dev/null 2>&1; then
  echo "Docker already installed: $(docker --version || true)"
fi

detect_os() {
  if [[ -r /etc/os-release ]]; then
    # shellcheck disable=SC1091
    . /etc/os-release
    echo "${ID:-unknown}" "${VERSION_CODENAME:-}" "${VERSION_ID:-}"
  else
    echo "unknown" "" ""
  fi
}

ID="" CODENAME="" VERSION_ID=""
read -r ID CODENAME VERSION_ID < <(detect_os)

echo "Detected OS: ID=${ID} CODENAME=${CODENAME} VERSION_ID=${VERSION_ID}"

setup_daemon_json() {
  mkdir -p /etc/docker
  if [[ ! -f /etc/docker/daemon.json ]]; then
    cat > /etc/docker/daemon.json <<'JSON'
{
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "10m",
    "max-file": "3"
  }
}
JSON
    echo "Created /etc/docker/daemon.json (log rotation)."
  else
    echo "/etc/docker/daemon.json already exists; leaving as-is."
  fi
}

install_debian_ubuntu() {
  apt-get update
  apt-get -y install ca-certificates curl gnupg

  install -m 0755 -d /etc/apt/keyrings
  curl -fsSL https://download.docker.com/linux/${ID}/gpg | gpg --dearmor -o /etc/apt/keyrings/docker.gpg
  chmod a+r /etc/apt/keyrings/docker.gpg

  ARCH="$(dpkg --print-architecture)"
  CODENAME_LOCAL="${CODENAME}"
  if [[ -z "${CODENAME_LOCAL}" ]]; then
    CODENAME_LOCAL="$(. /etc/os-release && echo "${VERSION_CODENAME}")"
  fi

  cat > /etc/apt/sources.list.d/docker.list <<EOF
deb [arch=${ARCH} signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/${ID} ${CODENAME_LOCAL} stable
EOF

  apt-get update
  apt-get -y install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
}

install_rhel_like() {
  # Works for: centos/rhel/almalinux/rocky/fedora (docker provides packages for many of these)
  if command -v dnf >/dev/null 2>&1; then
    PM="dnf"
  else
    PM="yum"
  fi

  $PM -y install yum-utils ca-certificates curl

  # Repo
  yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

  $PM -y install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
}

case "${ID}" in
  ubuntu|debian)
    install_debian_ubuntu
    ;;
  rhel|centos|fedora|rocky|almalinux)
    install_rhel_like
    ;;
  *)
    echo "Unsupported OS ID='${ID}'. Supported: ubuntu, debian, centos/rhel/rocky/almalinux/fedora" >&2
    exit 1
    ;;
esac

setup_daemon_json

systemctl enable docker
systemctl restart docker

# docker group/user permissions
if ! getent group docker >/dev/null; then
  groupadd docker || true
fi

if [[ "${ADD_TO_DOCKER_GROUP}" == "1" && -n "${TARGET_USER}" ]]; then
  if id "${TARGET_USER}" >/dev/null 2>&1; then
    usermod -aG docker "${TARGET_USER}"
    echo "Added user '${TARGET_USER}' to group 'docker'."
  else
    echo "User '${TARGET_USER}' not found; skipping docker group assignment." >&2
  fi
fi

echo
echo "=== Installed ==="
docker --version
docker compose version

echo
echo "=== Service status ==="
systemctl --no-pager --full status docker | sed -n '1,25p' || true

echo
if [[ "${ADD_TO_DOCKER_GROUP}" == "1" && -n "${TARGET_USER}" ]]; then
  echo "IMPORTANT: user '${TARGET_USER}' must re-login for docker group to apply."
  echo "Quick test after relogin: docker run --rm hello-world"
else
  echo "To use docker without sudo: add a user to docker group:"
  echo "  sudo usermod -aG docker <username> && newgrp docker"
fi