/*
Copyright 2022 The Kubernetes 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 topologymanager

import (
	"fmt"
	"io/ioutil"
	"strconv"
	"strings"

	cadvisorapi "github.com/google/cadvisor/info/v1"
	"k8s.io/kubernetes/pkg/kubelet/cm/topologymanager/bitmask"
)

const (
	defaultNodeDir = "/sys/devices/system/node/"
)

type NUMADistances [][]uint64

type NUMAInfo struct {
	Nodes         []int
	NUMADistances NUMADistances
}

type NUMASysFs struct {
	nodeDir string
}

func NewNUMAInfo(topology []cadvisorapi.Node) (*NUMAInfo, error) {
	return newNUMAInfo(topology, &NUMASysFs{nodeDir: defaultNodeDir})
}

func newNUMAInfo(topology []cadvisorapi.Node, sysFs *NUMASysFs) (*NUMAInfo, error) {
	var numaNodes []int
	distances := make([][]uint64, len(topology))
	for _, node := range topology {
		numaNodes = append(numaNodes, node.Id)

		// Populate the NUMA distances
		// For now we need to retrieve this information from sysfs.
		// TODO: Update this as follows once a version of cadvisor with this commit is vendored in https://github.com/google/cadvisor/commit/24dd1de08a72cfee661f6178454db995900c0fee
		//	distances[node.Id] = node.Distances[:]
		nodeDistance, err := sysFs.GetDistances(node.Id)
		if err != nil {
			return nil, fmt.Errorf("error getting NUMA distances from sysfs: %w", err)
		}
		distances[node.Id] = nodeDistance
	}

	numaInfo := &NUMAInfo{
		Nodes:         numaNodes,
		NUMADistances: distances,
	}

	return numaInfo, nil
}

func (n *NUMAInfo) Narrowest(m1 bitmask.BitMask, m2 bitmask.BitMask) bitmask.BitMask {
	if m1.IsNarrowerThan(m2) {
		return m1
	}
	return m2
}

func (n *NUMAInfo) Closest(m1 bitmask.BitMask, m2 bitmask.BitMask) bitmask.BitMask {
	// If the length of both bitmasks aren't the same, choose the one that is narrowest.
	if m1.Count() != m2.Count() {
		return n.Narrowest(m1, m2)
	}

	m1Distance := n.NUMADistances.CalculateAverageFor(m1)
	m2Distance := n.NUMADistances.CalculateAverageFor(m2)
	// If average distance is the same, take bitmask with more lower-number bits set.
	if m1Distance == m2Distance {
		if m1.IsLessThan(m2) {
			return m1
		}
		return m2
	}

	// Otherwise, return the bitmask with the shortest average distance between NUMA nodes.
	if m1Distance < m2Distance {
		return m1
	}

	return m2
}

func (n NUMAInfo) DefaultAffinityMask() bitmask.BitMask {
	defaultAffinity, _ := bitmask.NewBitMask(n.Nodes...)
	return defaultAffinity
}

func (d NUMADistances) CalculateAverageFor(bm bitmask.BitMask) float64 {
	// This should never happen, but just in case make sure we do not divide by zero.
	if bm.Count() == 0 {
		return 0
	}

	var count float64 = 0
	var sum float64 = 0
	for _, node1 := range bm.GetBits() {
		for _, node2 := range bm.GetBits() {
			sum += float64(d[node1][node2])
			count++
		}
	}

	return sum / count
}

func (s NUMASysFs) GetDistances(nodeId int) ([]uint64, error) {
	distancePath := fmt.Sprintf("%s/node%d/distance", s.nodeDir, nodeId)
	distance, err := ioutil.ReadFile(distancePath)
	if err != nil {
		return nil, fmt.Errorf("problem reading %s: %w", distancePath, err)
	}

	rawDistances := strings.TrimSpace(string(distance))

	return splitDistances(rawDistances)
}

func splitDistances(rawDistances string) ([]uint64, error) {
	distances := []uint64{}
	for _, distance := range strings.Split(rawDistances, " ") {
		distanceUint, err := strconv.ParseUint(distance, 10, 64)
		if err != nil {
			return nil, fmt.Errorf("cannot convert %s to int", distance)
		}
		distances = append(distances, distanceUint)
	}

	return distances, nil
}