package netxlite

//
// Bogon
//
// This file helps us to decide if an IPAddr is a bogon as well as
// a way to create a resolver that fails when resolving bogons.
//

import (
	"context"
	"net"

	"github.com/bassosimone/oonidsl/internal/model"
	"github.com/bassosimone/oonidsl/internal/runtimex"
)

// MaybeWrapWithBogonResolver wraps the given resolver with a BogonResolver
// iff the provided boolean flag is true. Otherwise, this factory just returns
// the provided resolver to the caller without any wrapping.
//
// The returned resolver returns a wrapped ErrDNSBogon if there's a bogon error.
//
// BUG: This resolver currently only implements LookupHost. All the other
// lookup methods will always return ErrNoDNSTransport.
func MaybeWrapWithBogonResolver(enabled bool, reso model.Resolver) model.Resolver {
	if enabled {
		reso = &bogonResolver{Resolver: reso}
	}
	return reso
}

// bogonResolver is a bogon aware resolver. When a bogon is encountered in
// a reply, this resolver will return ErrDNSBogon.
type bogonResolver struct {
	Resolver model.Resolver
}

var _ model.Resolver = &bogonResolver{}

// LookupHost implements Resolver.LookupHost
func (r *bogonResolver) LookupHost(ctx context.Context, hostname string) ([]string, error) {
	addrs, err := r.Resolver.LookupHost(ctx, hostname)
	if err != nil {
		return nil, err // not our responsibility to wrap this error
	}
	for _, addr := range addrs {
		if IsBogon(addr) {
			// wrap ErrDNSBogon as documented
			return nil, NewErrWrapper(ClassifyResolverError, ResolveOperation, ErrDNSBogon)
		}
	}
	return addrs, nil
}

// LookupHTTPS implements Resolver.LookupHTTPS
func (r *bogonResolver) LookupHTTPS(ctx context.Context, hostname string) (*model.HTTPSSvc, error) {
	// TODO(bassosimone): decide whether we want to implement this method or not
	return nil, ErrNoDNSTransport
}

// LookupNS implements Resolver.LookupNS
func (r *bogonResolver) LookupNS(ctx context.Context, hostname string) ([]*net.NS, error) {
	// TODO(bassosimone): decide whether we want to implement this method or not
	return nil, ErrNoDNSTransport
}

// Network implements Resolver.Network
func (r *bogonResolver) Network() string {
	return r.Resolver.Network()
}

// Address implements Resolver.Address
func (r *bogonResolver) Address() string {
	return r.Resolver.Address()
}

// CloseIdleConnections implements Resolver.CloseIdleConnections
func (r *bogonResolver) CloseIdleConnections() {
	r.Resolver.CloseIdleConnections()
}

// IsBogon returns whether an IP address is bogon. Passing to this
// function a non-IP address causes it to return true.
func IsBogon(address string) bool {
	ip := net.ParseIP(address)
	return ip == nil || isBogon(address, ip)
}

// IsLoopback returns whether an IP address is loopback. Passing to this
// function a non-IP address causes it to return true.
func IsLoopback(address string) bool {
	ip := net.ParseIP(address)
	return ip == nil || ip.IsLoopback()
}

var (
	bogons4 []*net.IPNet
	bogons6 []*net.IPNet
)

func expandBogons(cidrs []string) (out []*net.IPNet) {
	for _, cidr := range cidrs {
		_, block, err := net.ParseCIDR(cidr)
		runtimex.PanicOnError(err, "net.ParseCIDR failed")
		out = append(out, block)
	}
	return
}

func init() {
	bogons4 = append(bogons4, expandBogons([]string{
		//
		// List extracted from https://ipinfo.io/bogon
		//
		"0.0.0.0/8",          // "This" network
		"10.0.0.0/8",         // Private-use networks
		"100.64.0.0/10",      // Carrier-grade NAT
		"127.0.0.0/8",        // Loopback
		"127.0.53.53/32",     // Name collision occurrence
		"169.254.0.0/16",     // Link local
		"172.16.0.0/12",      // Private-use networks
		"192.0.0.0/24",       // IETF protocol assignments
		"192.0.2.0/24",       // TEST-NET-1
		"192.168.0.0/16",     // Private-use networks
		"198.18.0.0/15",      // Network interconnect device benchmark testing
		"198.51.100.0/24",    // TEST-NET-2
		"203.0.113.0/24",     // TEST-NET-3
		"224.0.0.0/4",        // Multicast
		"240.0.0.0/4",        // Reserved for future use
		"255.255.255.255/32", // Limited broadcast
	})...)
	bogons6 = append(bogons6, expandBogons([]string{
		//
		// List extracted from https://ipinfo.io/bogon
		//
		"::/128",                // Node-scope unicast unspecified address
		"::1/128",               // Node-scope unicast loopback address
		"::ffff:0:0/96",         // IPv4-mapped addresses
		"::/96",                 // IPv4-compatible addresses
		"100::/64",              // Remotely triggered black hole addresses
		"2001:10::/28",          // Overlay routable cryptographic hash identifiers (ORCHID)
		"2001:db8::/32",         // Documentation prefix
		"fc00::/7",              // Unique local addresses (ULA)
		"fe80::/10",             // Link-local unicast
		"fec0::/10",             // Site-local unicast (deprecated)
		"ff00::/8",              // Multicast (Note: ff0e:/16 is global scope and may appear on the global internet.)
		"2002::/24",             // 6to4 bogon (0.0.0.0/8)
		"2002:a00::/24",         // 6to4 bogon (10.0.0.0/8)
		"2002:7f00::/24",        // 6to4 bogon (127.0.0.0/8)
		"2002:a9fe::/32",        // 6to4 bogon (169.254.0.0/16)
		"2002:ac10::/28",        // 6to4 bogon (172.16.0.0/12)
		"2002:c000::/40",        // 6to4 bogon (192.0.0.0/24)
		"2002:c000:200::/40",    // 6to4 bogon (192.0.2.0/24)
		"2002:c0a8::/32",        // 6to4 bogon (192.168.0.0/16)
		"2002:c612::/31",        // 6to4 bogon (198.18.0.0/15)
		"2002:c633:6400::/40",   // 6to4 bogon (198.51.100.0/24)
		"2002:cb00:7100::/40",   // 6to4 bogon (203.0.113.0/24)
		"2002:e000::/20",        // 6to4 bogon (224.0.0.0/4)
		"2002:f000::/20",        // 6to4 bogon (240.0.0.0/4)
		"2002:ffff:ffff::/48",   // 6to4 bogon (255.255.255.255/32)
		"2001::/40",             // Teredo bogon (0.0.0.0/8)
		"2001:0:a00::/40",       // Teredo bogon (10.0.0.0/8)
		"2001:0:7f00::/40",      // Teredo bogon (127.0.0.0/8)
		"2001:0:a9fe::/48",      // Teredo bogon (169.254.0.0/16)
		"2001:0:ac10::/44",      // Teredo bogon (172.16.0.0/12)
		"2001:0:c000::/56",      // Teredo bogon (192.0.0.0/24)
		"2001:0:c000:200::/56",  // Teredo bogon (192.0.2.0/24)
		"2001:0:c0a8::/48",      // Teredo bogon (192.168.0.0/16)
		"2001:0:c612::/47",      // Teredo bogon (198.18.0.0/15)
		"2001:0:c633:6400::/56", // Teredo bogon (198.51.100.0/24)
		"2001:0:cb00:7100::/56", // Teredo bogon (203.0.113.0/24)
		"2001:0:e000::/36",      // Teredo bogon (224.0.0.0/4)
		"2001:0:f000::/36",      // Teredo bogon (240.0.0.0/4)
		"2001:0:ffff:ffff::/64", // Teredo bogon (255.255.255.255/32)
	})...)
}

// isBogon implements IsBogon
func isBogon(address string, ip net.IP) bool {
	// TODO(bassosimone): the following check is probably redundant given that these
	// three checks are already included into the list of bogons.
	if ip.IsLoopback() || ip.IsLinkLocalUnicast() || ip.IsLinkLocalMulticast() {
		return true
	}
	var bogons []*net.IPNet
	if isIPv6(address) {
		bogons = bogons6
	} else {
		bogons = bogons4
	}
	for _, block := range bogons {
		if block.Contains(ip) {
			return true
		}
	}
	return false
}
