package main

import (
	"fmt"
	"net"
	"strings"

	"github.com/gomodule/redigo/redis"
)

const (
	ipsKey = "gatekeeper/ips"
)

type subnetRange struct {
	Start  net.IP
	End    net.IP
	Subnet *net.IPNet
}

func (s *Server) getIPs() (map[string]net.IP, error) {
	c, err := s.getConn()
	if err != nil {
		return nil, err
	}
	defer c.Close()

	values, err := redis.StringMap(c.Do("HGETALL", ipsKey))
	if err != nil {
		return nil, err
	}

	ips := make(map[string]net.IP, len(values))
	for id, val := range values {
		ip := net.ParseIP(string(val))
		ips[id] = ip
	}
	return ips, nil
}

func (s *Server) getIP(id string) (net.IP, error) {
	allIPs, err := s.getIPs()
	if err != nil {
		return nil, err
	}

	if ip, exists := allIPs[id]; exists {
		return ip, nil
	}
	return nil, nil
}

func (s *Server) getOrAllocateIP(id, subnet string) (net.IP, *net.IPNet, error) {
	r, err := s.parseSubnetRange(subnet)
	if err != nil {
		return nil, nil, err
	}

	ip, err := s.getIP(id)
	if err != nil {
		return nil, nil, err
	}

	if ip != nil {
		return ip, r.Subnet, nil
	}

	ip, err = s.allocateIP(id, r)
	if err != nil {
		return nil, nil, err
	}

	return ip, r.Subnet, nil
}

func (s *Server) allocateIP(id string, r *subnetRange) (net.IP, error) {
	c, err := s.getConn()
	if err != nil {
		return nil, err
	}
	defer c.Close()

	reservedIPs, err := s.getIPs()
	if err != nil {
		return nil, err
	}

	if ip, exists := reservedIPs[id]; exists {
		return ip, nil
	}

	lookup := map[string]string{}
	for id, ip := range reservedIPs {
		lookup[ip.String()] = id
	}
	for ip := r.Start; !ip.Equal(r.End); s.nextIP(ip) {
		// filter out network, gateway and broadcast
		if !s.validIP(ip) {
			continue
		}
		if _, exists := lookup[ip.String()]; exists {
			// ip already reserved
			continue
		}

		// save
		if _, err := c.Do("HSET", ipsKey, id, ip.String()); err != nil {
			return nil, err
		}
		return ip, nil
	}

	return nil, fmt.Errorf("no available IPs")
}

func (s *Server) releaseIP(id string) error {
	c, err := s.getConn()
	if err != nil {
		return err
	}
	defer c.Close()

	ip, err := s.getIP(id)
	if err != nil {
		return err
	}

	if ip != nil {
		if _, err := c.Do("HDEL", ipsKey, id); err != nil {
			return err
		}
	}
	return nil
}

func (s *Server) nextIP(ip net.IP) {
	for j := len(ip) - 1; j >= 0; j-- {
		ip[j]++
		if ip[j] > 0 {
			break
		}
	}
}

func (s *Server) validIP(ip net.IP) bool {
	v := ip[len(ip)-1]
	switch v {
	case 0, 1, 255:
		return false
	}
	return true
}

// parseSubnetRange parses the subnet range
// format can either be a subnet like 10.0.0.0/8 or range like 10.0.0.100-10.0.0.200/24
func (s *Server) parseSubnetRange(subnet string) (*subnetRange, error) {
	parts := strings.Split(subnet, "-")
	if len(parts) == 1 {
		ip, sub, err := net.ParseCIDR(parts[0])
		if err != nil {
			return nil, err
		}

		end := make(net.IP, len(ip))
		copy(end, ip)
		end[len(end)-1] = 254
		return &subnetRange{
			Start:  ip,
			End:    end,
			Subnet: sub,
		}, nil
	}
	if len(parts) > 2 || !strings.Contains(subnet, "/") {
		return nil, fmt.Errorf("invalid range specified; expect format 10.0.0.100-10.0.0.200/24")
	}
	start := net.ParseIP(parts[0])
	end, sub, err := net.ParseCIDR(parts[1])
	if err != nil {
		return nil, err
	}

	return &subnetRange{
		Start:  start,
		End:    end,
		Subnet: sub,
	}, nil
}