#!/usr/bin/env bash
# shellcheck disable=SC2086

# Installs Docker Engine on Linux, or shows instructions for macOS/Windows.
# Docker: https://www.docker.com/
# OrbStack (macOS alternative): https://orbstack.dev/
#
# Supported platforms:
#   Linux (apt) : Ubuntu, Debian, and derivatives — Docker official apt repo
#   Linux (dnf) : RHEL, Fedora, CentOS Stream, Rocky, Alma — Docker official dnf repo
#   macOS       : Not supported — shows instructions for OrbStack or Docker Desktop
#   Windows     : Not supported — use install-docker.ps1 or Docker Desktop
#
# Prerequisites:
#   - Linux: curl, sudo
#   - macOS/Windows: follow the printed instructions

set -euo pipefail

# ────────────────────────────────────────────
# Constants
# ────────────────────────────────────────────
DOCKER_GPG_URL="https://download.docker.com/linux/ubuntu/gpg"
DOCKER_APT_REPO_URL="https://download.docker.com/linux/ubuntu"
DOCKER_DNF_REPO_URL="https://download.docker.com/linux/rhel/docker-ce.repo"

# ────────────────────────────────────────────
# Utility functions (all stderr output)
# ────────────────────────────────────────────
info() { echo "[INFO]  $*" >&2; }
warn() { echo "[WARN]  $*" >&2; }
error() {
	echo "[ERROR] $*" >&2
	exit 1
}
success() { echo "[OK]    $*" >&2; }

# ────────────────────────────────────────────
# Detect OS
# ────────────────────────────────────────────
OS="$(uname -s)"

case "$OS" in
Linux) ;;
Darwin)
	info "macOS detected. Docker Engine is not installed via this script on macOS."
	info ""
	info "Please install one of the following:"
	info ""
	info "  1. OrbStack (recommended, lightweight):"
	info "     https://orbstack.dev/"
	info ""
	info "  2. Docker Desktop for Mac:"
	info "     https://www.docker.com/products/docker-desktop/"
	info ""
	exit 0
	;;
*)
	info "Unsupported OS: $OS. This script only supports Linux."
	info ""
	info "For Windows, install one of the following:"
	info ""
	info "  1. Docker Desktop for Windows:"
	info "     https://www.docker.com/products/docker-desktop/"
	info ""
	info "  2. WSL2 with Docker Engine:"
	info "     Install WSL2, then run this script inside a WSL2 Linux distro."
	info ""
	exit 0
	;;
esac

ARCH="$(uname -m)"
info "Platform: $OS ($ARCH)"

# ────────────────────────────────────────────
# Check prerequisites
# ────────────────────────────────────────────
command -v curl &>/dev/null || error "'curl' is required. Install it first."
command -v sudo &>/dev/null || error "'sudo' is required."

# ────────────────────────────────────────────
# Step 1: Check if Docker is already installed
# ────────────────────────────────────────────
if command -v docker &>/dev/null; then
	CURRENT_VER="$(docker --version 2>/dev/null || echo 'unknown')"
	info "Docker is already installed ($CURRENT_VER). Skipping installation."
	info "To reinstall or upgrade, uninstall first: sudo apt remove docker-ce docker-ce-cli containerd.io"
	success "Docker is available: $(command -v docker)"
	exit 0
fi

# ────────────────────────────────────────────
# Step 2: Install Docker Engine
# ────────────────────────────────────────────
info "Installing Docker Engine..."

if command -v apt-get &>/dev/null; then
	# ── apt-based systems (Ubuntu, Debian, etc.) ──
	info "Detected apt-based system. Using Docker official apt repository..."

	# Add Docker's official GPG key
	sudo apt-get update -y
	sudo apt-get install -y ca-certificates curl
	sudo install -m 0755 -d /etc/apt/keyrings
	sudo curl -fsSL "$DOCKER_GPG_URL" -o /etc/apt/keyrings/docker.asc
	sudo chmod a+r /etc/apt/keyrings/docker.asc

	# Add the repository to Apt sources
	CODENAME="$(. /etc/os-release && echo "${UBUNTU_CODENAME:-$VERSION_CODENAME}")"
	ARCH_DEB="$(dpkg --print-architecture)"
	sudo tee /etc/apt/sources.list.d/docker.sources >/dev/null <<EOF
Types: deb
URIs: ${DOCKER_APT_REPO_URL}
Suites: ${CODENAME}
Components: stable
Architectures: ${ARCH_DEB}
Signed-By: /etc/apt/keyrings/docker.asc
EOF
	sudo apt-get update -y

	# Install Docker packages
	sudo apt-get install -y docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
	success "Docker installed via apt"

elif command -v dnf &>/dev/null; then
	# ── dnf-based systems (RHEL, Fedora, CentOS Stream, Rocky, Alma) ──
	info "Detected dnf-based system. Using Docker official dnf repository..."

	sudo dnf config-manager --add-repo "$DOCKER_DNF_REPO_URL"
	sudo dnf -y install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
	sudo systemctl --now enable docker
	success "Docker installed via dnf"

else
	error "No supported package manager found (apt-get or dnf). Install Docker manually: https://docs.docker.com/engine/install/"
fi

# ────────────────────────────────────────────
# Step 3: Add current user to docker group
# ────────────────────────────────────────────
info "Adding current user to the docker group..."
sudo usermod -aG docker "$(whoami)"
success "User '$(whoami)' added to the docker group"

info ""
info "NOTE: Group membership takes effect on next login."
info "      To apply immediately in this session, run: newgrp docker"
info "      Or log out and log back in."

# ────────────────────────────────────────────
# Step 4: Verify installation
# ────────────────────────────────────────────
if command -v docker &>/dev/null; then
	DOCKER_VER="$(docker --version 2>/dev/null || echo 'unknown')"
	success "Docker is available: $DOCKER_VER"
else
	# May need a new shell for group changes
	warn "Docker was installed but 'docker' command not found in current PATH."
	warn "Please open a new terminal or run: newgrp docker"
fi

# ────────────────────────────────────────────
# Step 5: Post-install notes
# ────────────────────────────────────────────
info ""
info "=================================================="
success "Docker installation complete!"
info "=================================================="
info ""
info "Getting started:"
info "  docker run hello-world         - Verify installation"
info "  docker ps                       - List running containers"
info "  docker compose up -d           - Start services with Compose"
info "  docker build -t <name> .       - Build an image"
info ""
info "Post-install steps (optional):"
info "  https://docs.docker.com/engine/install/linux-post-install/"
info ""
info "Manage Docker as non-root:"
info "  You have been added to the 'docker' group."
info "  Log out and back in for this to take effect."
info ""
info "Container monitoring with ctop:"
info "  Install ctop to monitor containers: install-ctop.sh"