package cloudinit

import (
	"fmt"
	"log/slog"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
)

// ApplyNetwork configures the network interface based on cloud-init config.
// For static mode, it sets the IP, gateway, and DNS directly.
// For DHCP mode, it runs udhcpc on the target interface.
func ApplyNetwork(cfg *Config) error {
	iface := cfg.Network.Interface
	if iface == "" {
		var err error
		iface, err = detectPrimaryInterface()
		if err != nil {
			return fmt.Errorf("detecting primary interface: %w", err)
		}
	}

	slog.Info("configuring network", "interface", iface, "mode", cfg.Network.Mode)

	// Bring up the interface
	if err := run("ip", "link", "set", iface, "up"); err != nil {
		return fmt.Errorf("bringing up %s: %w", iface, err)
	}

	switch cfg.Network.Mode {
	case "static":
		return applyStatic(iface, cfg)
	case "dhcp", "":
		return applyDHCP(iface, cfg)
	default:
		return fmt.Errorf("unknown network mode: %s", cfg.Network.Mode)
	}
}

func applyStatic(iface string, cfg *Config) error {
	// Set IP address
	if err := run("ip", "addr", "add", cfg.Network.Address, "dev", iface); err != nil {
		return fmt.Errorf("setting address %s on %s: %w", cfg.Network.Address, iface, err)
	}

	// Set default gateway
	if err := run("ip", "route", "add", "default", "via", cfg.Network.Gateway, "dev", iface); err != nil {
		return fmt.Errorf("setting gateway %s: %w", cfg.Network.Gateway, err)
	}

	// Write DNS configuration
	if len(cfg.Network.DNS) > 0 {
		if err := writeDNS(cfg.Network.DNS); err != nil {
			return fmt.Errorf("writing DNS config: %w", err)
		}
	}

	slog.Info("static network configured",
		"interface", iface,
		"address", cfg.Network.Address,
		"gateway", cfg.Network.Gateway,
	)
	return nil
}

func applyDHCP(iface string, cfg *Config) error {
	// Try udhcpc (BusyBox), then dhcpcd
	if path, err := exec.LookPath("udhcpc"); err == nil {
		args := []string{"-i", iface, "-s", "/usr/share/udhcpc/default.script",
			"-t", "10", "-T", "3", "-A", "5", "-b", "-q"}
		if err := run(path, args...); err != nil {
			return fmt.Errorf("udhcpc on %s: %w", iface, err)
		}
	} else if path, err := exec.LookPath("dhcpcd"); err == nil {
		if err := run(path, iface); err != nil {
			return fmt.Errorf("dhcpcd on %s: %w", iface, err)
		}
	} else {
		return fmt.Errorf("no DHCP client available (need udhcpc or dhcpcd)")
	}

	// Override DNS if specified in config
	if len(cfg.Network.DNS) > 0 {
		if err := writeDNS(cfg.Network.DNS); err != nil {
			return fmt.Errorf("writing DNS config: %w", err)
		}
	}

	slog.Info("DHCP network configured", "interface", iface)
	return nil
}

// SaveNetworkConfig writes a shell script that restores the current network
// config on subsequent boots (before cloud-init runs).
func SaveNetworkConfig(cfg *Config, destDir string) error {
	iface := cfg.Network.Interface
	if iface == "" {
		var err error
		iface, err = detectPrimaryInterface()
		if err != nil {
			return err
		}
	}

	if err := os.MkdirAll(destDir, 0o755); err != nil {
		return fmt.Errorf("creating network config dir: %w", err)
	}

	dest := filepath.Join(destDir, "interfaces.sh")
	var sb strings.Builder
	sb.WriteString("#!/bin/sh\n")
	sb.WriteString("# Auto-generated by KubeSolo OS cloud-init\n")
	sb.WriteString(fmt.Sprintf("ip link set %s up\n", iface))

	switch cfg.Network.Mode {
	case "static":
		sb.WriteString(fmt.Sprintf("ip addr add %s dev %s\n", cfg.Network.Address, iface))
		sb.WriteString(fmt.Sprintf("ip route add default via %s dev %s\n", cfg.Network.Gateway, iface))
		if len(cfg.Network.DNS) > 0 {
			sb.WriteString(": > /etc/resolv.conf\n")
			for _, ns := range cfg.Network.DNS {
				sb.WriteString(fmt.Sprintf("echo 'nameserver %s' >> /etc/resolv.conf\n", ns))
			}
		}
	case "dhcp", "":
		sb.WriteString("udhcpc -i " + iface + " -s /usr/share/udhcpc/default.script -t 10 -T 3 -A 5 -b -q 2>/dev/null\n")
	}

	if err := os.WriteFile(dest, []byte(sb.String()), 0o755); err != nil {
		return fmt.Errorf("writing network config: %w", err)
	}

	slog.Info("network config saved", "path", dest)
	return nil
}

func writeDNS(servers []string) error {
	var sb strings.Builder
	for _, ns := range servers {
		sb.WriteString("nameserver " + ns + "\n")
	}
	return os.WriteFile("/etc/resolv.conf", []byte(sb.String()), 0o644)
}

func detectPrimaryInterface() (string, error) {
	entries, err := os.ReadDir("/sys/class/net")
	if err != nil {
		return "", fmt.Errorf("reading /sys/class/net: %w", err)
	}
	for _, e := range entries {
		name := e.Name()
		switch {
		case name == "lo",
			strings.HasPrefix(name, "docker"),
			strings.HasPrefix(name, "veth"),
			strings.HasPrefix(name, "br"),
			strings.HasPrefix(name, "cni"),
			strings.HasPrefix(name, "flannel"),
			strings.HasPrefix(name, "cali"):
			continue
		}
		return name, nil
	}
	return "", fmt.Errorf("no suitable network interface found")
}

func run(name string, args ...string) error {
	cmd := exec.Command(name, args...)
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	return cmd.Run()
}