package config

import (
	"fmt"
	"net"
)

type NetmapType string

const (
	NetmapDNAT NetmapType = "dnat"
	NetmapSNAT NetmapType = "snat"
)

// Netmap maps addresses in one network to corresponding addresses in another.
// For DNAT: traffic entering the interface addressed to Net1 has its dest rewritten to Net2.
// For SNAT: traffic leaving the interface with source in Net1 has its source rewritten to Net2.
type Netmap struct {
	Type NetmapType `yaml:"type"`

	// Network in CIDR format to match.
	Net1 string `yaml:"net1"`

	// Interface name (must be defined in interfaces).
	Interface string `yaml:"interface"`

	// Network in CIDR format to rewrite to.
	Net2 string `yaml:"net2"`

	// Optional qualifying network: source for DNAT rules, destination for SNAT rules.
	Net3 string `yaml:"net3,omitempty"`

	Proto string   `yaml:"proto,omitempty"`
	DPort PortSpec `yaml:"dport,omitempty"`
	SPort PortSpec `yaml:"sport,omitempty"`

	Comment string `yaml:"comment,omitempty"`
}

func (c *Config) validateNetmap() error {
	for i, nm := range c.Netmap {
		switch nm.Type {
		case NetmapDNAT, NetmapSNAT:
		default:
			return fmt.Errorf("netmap[%d]: type must be dnat or snat, got %q", i, nm.Type)
		}

		if nm.Net1 == "" {
			return fmt.Errorf("netmap[%d]: net1 required", i)
		}
		if _, _, err := net.ParseCIDR(nm.Net1); err != nil {
			return fmt.Errorf("netmap[%d]: net1 must be CIDR format: %w", i, err)
		}

		if nm.Interface == "" {
			return fmt.Errorf("netmap[%d]: interface required", i)
		}
		ifaceFound := false
		for _, iface := range c.Interfaces {
			if iface.Interface == nm.Interface || iface.PhysicalName() == nm.Interface {
				ifaceFound = true
				break
			}
		}
		if !ifaceFound {
			return fmt.Errorf("netmap[%d]: interface %q not defined in interfaces", i, nm.Interface)
		}

		if nm.Net2 == "" {
			return fmt.Errorf("netmap[%d]: net2 required", i)
		}
		if _, _, err := net.ParseCIDR(nm.Net2); err != nil {
			return fmt.Errorf("netmap[%d]: net2 must be CIDR format: %w", i, err)
		}

		if nm.Net3 != "" {
			if _, _, err := net.ParseCIDR(nm.Net3); err != nil {
				return fmt.Errorf("netmap[%d]: net3 must be CIDR format: %w", i, err)
			}
		}
	}
	return nil
}