package cloudinit

import (
	"fmt"
	"log/slog"
	"os"
	"strings"
)

// ApplyHostname sets the system hostname and updates /etc/hostname and /etc/hosts.
func ApplyHostname(cfg *Config) error {
	hostname := cfg.Hostname
	if hostname == "" {
		slog.Info("no hostname in cloud-init, skipping")
		return nil
	}

	// Set the running hostname
	if err := os.WriteFile("/proc/sys/kernel/hostname", []byte(hostname), 0o644); err != nil {
		// Fallback: use the hostname command
		if err := run("hostname", hostname); err != nil {
			return fmt.Errorf("setting hostname: %w", err)
		}
	}

	// Write /etc/hostname
	if err := os.WriteFile("/etc/hostname", []byte(hostname+"\n"), 0o644); err != nil {
		return fmt.Errorf("writing /etc/hostname: %w", err)
	}

	// Ensure hostname is in /etc/hosts
	if err := ensureHostsEntry(hostname); err != nil {
		return fmt.Errorf("updating /etc/hosts: %w", err)
	}

	slog.Info("hostname set", "hostname", hostname)
	return nil
}

// SaveHostname writes the hostname to the persistent data partition so it
// survives reboots (even without cloud-init on next boot).
func SaveHostname(cfg *Config, destDir string) error {
	if cfg.Hostname == "" {
		return nil
	}
	if err := os.MkdirAll(destDir, 0o755); err != nil {
		return fmt.Errorf("creating hostname dir: %w", err)
	}
	dest := destDir + "/hostname"
	if err := os.WriteFile(dest, []byte(cfg.Hostname+"\n"), 0o644); err != nil {
		return fmt.Errorf("writing persistent hostname: %w", err)
	}
	slog.Info("hostname saved", "path", dest)
	return nil
}

func ensureHostsEntry(hostname string) error {
	data, err := os.ReadFile("/etc/hosts")
	if err != nil && !os.IsNotExist(err) {
		return err
	}

	content := string(data)
	entry := "127.0.0.1 " + hostname

	// Check if already present
	for _, line := range strings.Split(content, "\n") {
		if strings.Contains(line, hostname) {
			return nil
		}
	}

	// Append
	if !strings.HasSuffix(content, "\n") && content != "" {
		content += "\n"
	}
	content += entry + "\n"

	return os.WriteFile("/etc/hosts", []byte(content), 0o644)
}