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

log() {
  printf '\n[%s] %s\n' "$(date -u +'%Y-%m-%d %H:%M:%S UTC')" "$*"
}

require_root() {
  if [[ ${EUID:-$(id -u)} -ne 0 ]]; then
    echo "Please run this script as root or with sudo." >&2
    exit 1
  fi
}

command_exists() {
  command -v "$1" >/dev/null 2>&1
}

get_os_info() {
  if [[ ! -f /etc/os-release ]]; then
    echo "Cannot detect OS: /etc/os-release not found." >&2
    exit 1
  fi

  # shellcheck disable=SC1091
  . /etc/os-release
  OS_ID="${ID:-}"
  OS_LIKE="${ID_LIKE:-}"
  OS_VERSION_ID="${VERSION_ID:-}"
  OS_CODENAME="${UBUNTU_CODENAME:-${VERSION_CODENAME:-}}"
  OS_NAME="${PRETTY_NAME:-${NAME:-unknown}}"
}

install_debian_family() {
  log "Detected Debian/Ubuntu family: ${OS_NAME}"

  apt update
  apt install -y ca-certificates curl
  install -m 0755 -d /etc/apt/keyrings

  local repo_base
  case "$OS_ID" in
    ubuntu)
      repo_base="https://download.docker.com/linux/ubuntu"
      ;;
    debian)
      repo_base="https://download.docker.com/linux/debian"
      ;;
    *)
      # Fallback for derivatives
      repo_base="https://download.docker.com/linux/ubuntu"
      ;;
  esac

  curl -fsSL "${repo_base}/gpg" -o /etc/apt/keyrings/docker.asc
  chmod a+r /etc/apt/keyrings/docker.asc

  if [[ -z "${OS_CODENAME}" ]]; then
    echo "Could not determine distro codename from /etc/os-release." >&2
    exit 1
  fi

  cat >/etc/apt/sources.list.d/docker.sources <<EOF
Types: deb
URIs: ${repo_base}
Suites: ${OS_CODENAME}
Components: stable
Architectures: $(dpkg --print-architecture)
Signed-By: /etc/apt/keyrings/docker.asc
EOF

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

  if command_exists systemctl; then
    if systemctl is-enabled docker >/dev/null 2>&1 || systemctl enable --now docker; then
      log "Docker service enabled and started."
    else
      log "Docker installed, but systemd could not enable/start it automatically."
      systemctl start docker || true
    fi
  fi
}

install_rhel_family() {
  log "Detected RHEL/Alma/Rocky/CentOS family: ${OS_NAME}"

  if ! command_exists dnf; then
    echo "dnf is required for RHEL-family installation but was not found." >&2
    exit 1
  fi

  dnf -y install dnf-plugins-core
  dnf config-manager --add-repo https://download.docker.com/linux/rhel/docker-ce.repo
  dnf -y install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

  if command_exists systemctl; then
    systemctl enable --now docker
    log "Docker service enabled and started."
  fi
}

verify_install() {
  log "Verifying installation"

  if command_exists docker; then
    docker --version
  else
    echo "docker command not found after installation." >&2
    exit 1
  fi

  if docker compose version; then
    :
  else
    echo "docker compose plugin not available after installation." >&2
    exit 1
  fi

  if command_exists systemctl; then
    systemctl --no-pager --full status docker || true
  fi
}

main() {
  require_root
  get_os_info

  case "$OS_ID" in
    ubuntu|debian)
      install_debian_family
      ;;
    almalinux|rhel|rocky|centos|fedora)
      install_rhel_family
      ;;
    *)
      if [[ "$OS_LIKE" == *debian* ]]; then
        install_debian_family
      elif [[ "$OS_LIKE" == *rhel* ]] || [[ "$OS_LIKE" == *fedora* ]]; then
        install_rhel_family
      else
        echo "Unsupported OS: ${OS_NAME} (ID=${OS_ID}, ID_LIKE=${OS_LIKE})" >&2
        exit 1
      fi
      ;;
  esac

  verify_install
  log "Done."
}

main "$@"