// Package mnet extends the standard package with extra functionality which is
// commonly useful
package mnet

import (
	"net"

	"github.com/mediocregopher/mediocre-go-lib/mcfg"
	"github.com/mediocregopher/mediocre-go-lib/mctx"
	"github.com/mediocregopher/mediocre-go-lib/mlog"
	"github.com/mediocregopher/mediocre-go-lib/mrun"
)

// ListenerOnStart returns a Listener which will be initialized when the start
// event is triggered on ctx (see mrun.Start).
//
// network defaults to "tcp" if empty. defaultAddr defaults to ":0" if empty,
// and will be configurable via mcfg.
func ListenerOnStart(ctx mctx.Context, network, defaultAddr string) net.Listener {
	if network == "" {
		network = "tcp"
	}
	if defaultAddr == "" {
		defaultAddr = ":0"
	}
	addr := mcfg.String(ctx, "addr", defaultAddr, network+" address to listen on in format [host]:port. If port is 0 then a random one will be chosen")

	var l struct{ net.Listener }
	mrun.OnStart(ctx, func(mctx.Context) error {
		var err error
		if l.Listener, err = net.Listen(network, *addr); err != nil {
			return err
		}
		mlog.From(ctx).Info("listening", mlog.KV{"addr": l.Addr()})
		return nil
	})

	return &l
}

////////////////////////////////////////////////////////////////////////////////

func mustGetCIDRNetwork(cidr string) *net.IPNet {
	_, n, err := net.ParseCIDR(cidr)
	if err != nil {
		panic(err)
	}
	return n
}

// https://en.wikipedia.org/wiki/Reserved_IP_addresses

var reservedCIDRs4 = []*net.IPNet{
	mustGetCIDRNetwork("0.0.0.0/8"),          // current network
	mustGetCIDRNetwork("10.0.0.0/8"),         // private network
	mustGetCIDRNetwork("100.64.0.0/10"),      // private network
	mustGetCIDRNetwork("127.0.0.0/8"),        // localhost
	mustGetCIDRNetwork("169.254.0.0/16"),     // link-local
	mustGetCIDRNetwork("172.16.0.0/12"),      // private network
	mustGetCIDRNetwork("192.0.0.0/24"),       // IETF protocol assignments
	mustGetCIDRNetwork("192.0.2.0/24"),       // documentation and examples
	mustGetCIDRNetwork("192.88.99.0/24"),     // 6to4 Relay
	mustGetCIDRNetwork("192.168.0.0/16"),     // private network
	mustGetCIDRNetwork("198.18.0.0/15"),      // private network
	mustGetCIDRNetwork("198.51.100.0/24"),    // documentation and examples
	mustGetCIDRNetwork("203.0.113.0/24"),     // documentation and examples
	mustGetCIDRNetwork("224.0.0.0/4"),        // IP multicast
	mustGetCIDRNetwork("240.0.0.0/4"),        // reserved
	mustGetCIDRNetwork("255.255.255.255/32"), // limited broadcast address
}

var reservedCIDRs6 = []*net.IPNet{
	mustGetCIDRNetwork("::/128"),        // unspecified address
	mustGetCIDRNetwork("::1/128"),       // loopback address
	mustGetCIDRNetwork("100::/64"),      // discard prefix
	mustGetCIDRNetwork("2001::/32"),     // Teredo tunneling
	mustGetCIDRNetwork("2001:20::/28"),  // ORCHID v2
	mustGetCIDRNetwork("2001:db8::/32"), // documentation and examples
	mustGetCIDRNetwork("2002::/16"),     // 6to4 addressing
	mustGetCIDRNetwork("fc00::/7"),      // unique local
	mustGetCIDRNetwork("fe80::/10"),     // link local
	mustGetCIDRNetwork("ff00::/8"),      // multicast
}

// IsReservedIP returns true if the given valid IP is part of a reserved IP
// range.
func IsReservedIP(ip net.IP) bool {
	containedBy := func(cidrs []*net.IPNet) bool {
		for _, cidr := range cidrs {
			if cidr.Contains(ip) {
				return true
			}
		}
		return false
	}

	if ip.To4() != nil {
		return containedBy(reservedCIDRs4)
	}
	return containedBy(reservedCIDRs6)
}