// Copyright 2017 CNI authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package allocator

import (
	"fmt"
	"net"

	"github.com/containernetworking/cni/pkg/types"
	"github.com/containernetworking/plugins/pkg/ip"
)

// Canonicalize takes a given range and ensures that all information is consistent,
// filling out Start, End, and Gateway with sane values if missing
func (r *Range) Canonicalize() error {
	if err := canonicalizeIP(&r.Subnet.IP); err != nil {
		return err
	}

	// Can't create an allocator for a network with no addresses, eg
	// a /32 or /31
	ones, masklen := r.Subnet.Mask.Size()
	if ones > masklen-2 {
		return fmt.Errorf("Network %s too small to allocate from", (*net.IPNet)(&r.Subnet).String())
	}

	if len(r.Subnet.IP) != len(r.Subnet.Mask) {
		return fmt.Errorf("IPNet IP and Mask version mismatch")
	}

	// Ensure Subnet IP is the network address, not some other address
	networkIP := r.Subnet.IP.Mask(r.Subnet.Mask)
	if !r.Subnet.IP.Equal(networkIP) {
		return fmt.Errorf("Network has host bits set. For a subnet mask of length %d the network address is %s", ones, networkIP.String())
	}

	// If the gateway is nil, claim .1
	if r.Gateway == nil {
		r.Gateway = ip.NextIP(r.Subnet.IP)
	} else {
		if err := canonicalizeIP(&r.Gateway); err != nil {
			return err
		}
	}

	// RangeStart: If specified, make sure it's sane (inside the subnet),
	// otherwise use the first free IP (i.e. .1) - this will conflict with the
	// gateway but we skip it in the iterator
	if r.RangeStart != nil {
		if err := canonicalizeIP(&r.RangeStart); err != nil {
			return err
		}

		if !r.Contains(r.RangeStart) {
			return fmt.Errorf("RangeStart %s not in network %s", r.RangeStart.String(), (*net.IPNet)(&r.Subnet).String())
		}
	} else {
		r.RangeStart = ip.NextIP(r.Subnet.IP)
	}

	// RangeEnd: If specified, verify sanity. Otherwise, add a sensible default
	// (e.g. for a /24: .254 if IPv4, ::255 if IPv6)
	if r.RangeEnd != nil {
		if err := canonicalizeIP(&r.RangeEnd); err != nil {
			return err
		}

		if !r.Contains(r.RangeEnd) {
			return fmt.Errorf("RangeEnd %s not in network %s", r.RangeEnd.String(), (*net.IPNet)(&r.Subnet).String())
		}
	} else {
		r.RangeEnd = lastIP(r.Subnet)
	}

	return nil
}

// IsValidIP checks if a given ip is a valid, allocatable address in a given Range
func (r *Range) Contains(addr net.IP) bool {
	if err := canonicalizeIP(&addr); err != nil {
		return false
	}

	subnet := (net.IPNet)(r.Subnet)

	// Not the same address family
	if len(addr) != len(r.Subnet.IP) {
		return false
	}

	// Not in network
	if !subnet.Contains(addr) {
		return false
	}

	// We ignore nils here so we can use this function as we initialize the range.
	if r.RangeStart != nil {
		// Before the range start
		if ip.Cmp(addr, r.RangeStart) < 0 {
			return false
		}
	}

	if r.RangeEnd != nil {
		if ip.Cmp(addr, r.RangeEnd) > 0 {
			// After the  range end
			return false
		}
	}

	return true
}

// Overlaps returns true if there is any overlap between ranges
func (r *Range) Overlaps(r1 *Range) bool {
	// different familes
	if len(r.RangeStart) != len(r1.RangeStart) {
		return false
	}

	return r.Contains(r1.RangeStart) ||
		r.Contains(r1.RangeEnd) ||
		r1.Contains(r.RangeStart) ||
		r1.Contains(r.RangeEnd)
}

func (r *Range) String() string {
	return fmt.Sprintf("%s-%s", r.RangeStart.String(), r.RangeEnd.String())
}

// canonicalizeIP makes sure a provided ip is in standard form
func canonicalizeIP(ip *net.IP) error {
	if ip.To4() != nil {
		*ip = ip.To4()
		return nil
	} else if ip.To16() != nil {
		*ip = ip.To16()
		return nil
	}
	return fmt.Errorf("IP %s not v4 nor v6", *ip)
}

// Determine the last IP of a subnet, excluding the broadcast if IPv4
func lastIP(subnet types.IPNet) net.IP {
	var end net.IP
	for i := 0; i < len(subnet.IP); i++ {
		end = append(end, subnet.IP[i]|^subnet.Mask[i])
	}
	if subnet.IP.To4() != nil {
		end[3]--
	}

	return end
}