package synthetic

import (
	"fmt"
	"net"
	"strconv"
	"strings"

	"github.com/coredns/caddy"
	"github.com/coredns/coredns/core/dnsserver"
	"github.com/coredns/coredns/plugin"
)

// syntheticConfig holds the parsed Corefile configuration for the synthetic plugin.
type syntheticConfig struct {
	// net is the set of IP networks for which synthetic forward responses are
	// generated. Only addresses falling within these CIDRs will be resolved.
	net []*net.IPNet

	// forward is the DNS zone appended to synthetic hostnames when generating
	// PTR records (e.g., "example.com").
	forward string

	// ttl is the time-to-live value applied to all synthetic responses.
	// Defaults to 0 (no caching).
	ttl uint32

	// prefix is the hostname label prefix used to identify synthetic queries
	// (e.g., "ip-"). A trailing dash is appended automatically if absent.
	prefix string
}

func init() { plugin.Register("synthetic", setup) }

// setup parses the Corefile configuration block for the synthetic plugin and
// registers it in the CoreDNS handler chain.
func setup(c *caddy.Controller) error {
	config, err := parseConfig(c)
	if err != nil {
		return err
	}

	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
		return synthetic{Next: next, Config: config}
	})

	return nil
}

// parseConfig reads the synthetic { ... } block from the Corefile and returns
// a validated syntheticConfig.
func parseConfig(c *caddy.Controller) (syntheticConfig, error) {
	var config syntheticConfig

	for c.Next() {
		for c.NextBlock() {
			switch v := c.Val(); v {
			case "net":
				for _, arg := range c.RemainingArgs() {
					_, cidr, err := net.ParseCIDR(arg)
					if err != nil {
						return config, fmt.Errorf("synthetic: invalid CIDR notation: %v", arg)
					}
					config.net = append(config.net, cidr)
				}

			case "forward":
				args := c.RemainingArgs()
				if len(args) > 0 {
					config.forward = args[0]
				}

			case "ttl":
				for _, arg := range c.RemainingArgs() {
					ttl64, err := strconv.ParseUint(arg, 10, 32)
					if err != nil {
						return config, fmt.Errorf("synthetic: invalid ttl value: %v", arg)
					}
					config.ttl = uint32(ttl64)
				}

			case "prefix":
				args := c.RemainingArgs()
				if len(args) > 0 {
					config.prefix = args[0]
				}

			default:
				return config, c.Errf("unknown property '%s'", v)
			}
		}
	}

	// Apply defaults.
	if config.prefix == "" {
		config.prefix = "ip"
	}
	if !strings.HasSuffix(config.prefix, "-") {
		config.prefix += "-"
	}

	return config, nil
}