#!/bin/bash
set -euo pipefail

# Install Docker Engine on Debian/Ubuntu using Docker's official apt repository.
# Follows the official docs:
#   https://docs.docker.com/engine/install/debian/
#   https://docs.docker.com/engine/install/ubuntu/

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

. /etc/os-release

case "$ID" in
  debian|ubuntu) ;;
  *)
    echo "Unsupported distribution: $ID (only Debian and Ubuntu are supported)." >&2
    exit 1
    ;;
esac

# Optional override for derivative distros (e.g. Kali, Linux Mint) whose
# codename doesn't match an official Docker release. Example:
#   DOCKER_CODENAME=trixie ./install-docker.sh
CODENAME="${DOCKER_CODENAME:-${UBUNTU_CODENAME:-$VERSION_CODENAME}}"

ARCH="$(dpkg --print-architecture)"
case "$ARCH" in
  amd64|armhf|arm64|ppc64el|s390x) ;;
  *)
    echo "Unsupported architecture: $ARCH" >&2
    exit 1
    ;;
esac

export DEBIAN_FRONTEND=noninteractive

echo "==> Removing conflicting packages (if any)"
CONFLICTS="$(dpkg --get-selections \
  docker.io docker-compose docker-compose-v2 docker-doc docker-buildx \
  podman-docker containerd runc 2>/dev/null | awk '{print $1}')"
if [ -n "$CONFLICTS" ]; then
  # shellcheck disable=SC2086
  apt-get remove -y $CONFLICTS
fi

echo "==> Installing prerequisites"
apt-get update
apt-get install -y ca-certificates curl

echo "==> Adding Docker's official GPG key"
install -m 0755 -d /etc/apt/keyrings
curl -fsSL "https://download.docker.com/linux/$ID/gpg" -o /etc/apt/keyrings/docker.asc
chmod a+r /etc/apt/keyrings/docker.asc

echo "==> Adding Docker apt repository"
tee /etc/apt/sources.list.d/docker.sources >/dev/null <<EOF
Types: deb
URIs: https://download.docker.com/linux/$ID
Suites: $CODENAME
Components: stable
Architectures: $ARCH
Signed-By: /etc/apt/keyrings/docker.asc
EOF

echo "==> Installing Docker Engine"
apt-get update
apt-get install -y docker-ce docker-ce-cli containerd.io \
  docker-buildx-plugin docker-compose-plugin

echo "==> Enabling and starting Docker"
systemctl enable --now docker

echo "==> Verifying installation"
if docker run --rm hello-world; then
  echo "hello-world ran successfully."
else
  echo "Warning: could not run hello-world (check network access to Docker Hub)." >&2
fi

# Post-install: let the invoking (non-root) user run docker without sudo
if [ -n "${SUDO_USER:-}" ] && [ "$SUDO_USER" != "root" ]; then
  usermod -aG docker "$SUDO_USER"
  echo "Added user '$SUDO_USER' to the 'docker' group."
  echo "Log out and back in (or run 'newgrp docker') for the change to take effect."
fi

echo
echo "Docker installed successfully."
echo "Check version:  docker --version"
echo "Check compose:  docker compose version"