package node

import (
	"github.com/shirou/gopsutil/cpu"
	"github.com/shirou/gopsutil/disk"
	"github.com/shirou/gopsutil/load"
	"github.com/shirou/gopsutil/mem"

	"github.com/jinzhu/gorm"
)

const history = 72 * 3600 / 300 //  3 days, one record every five minutes

// Processor covers Node related methods for monitoring and calculating performance indexes.
type Processor struct {
	DB *gorm.DB
}

func (p *Processor) Init() {
	p.DB.AutoMigrate(PerformanceLog{})
}

// GetNodeInfo returns information about this node
func (p *Processor) GetNodeInfo() (*Node, error) {
	node, err := p.Index()
	return node, err
}

// Log creates a record for all important metrics used as
func (p *Processor) Log() error {
	performanceLog := PerformanceLog{}

	// Load
	loadStats, err := load.Avg()
	if err != nil {
		return err
	}

	performanceLog.Load1 = loadStats.Load1
	performanceLog.Load5 = loadStats.Load5
	performanceLog.Load15 = loadStats.Load15

	// Memory
	memoryStat, err := mem.VirtualMemory()
	if err != nil {
		return err
	}
	performanceLog.Memory = memoryStat.UsedPercent / 100.0

	// Disk space
	diskUsage, err := disk.Usage("/srv")
	if err != nil {
		return err
	}
	performanceLog.DiskSpaceUsage = diskUsage.UsedPercent / 100.0

	// Save
	err = p.DB.Create(&performanceLog).Error
	if err != nil {
		return err
	}

	// and clean
	// we have to use this stupid approach because DELETE doesn't support ORDER BY and LIMIT
	toDeleteLogs := []PerformanceLog{}
	err = p.DB.Order("id DESC").Limit("99").Offset(history).Find(&toDeleteLogs).Error
	if err != nil {
		return err
	}

	for _, toDeleteLog := range toDeleteLogs {
		err = p.DB.Delete(&toDeleteLog).Error
		if err != nil {
			return err
		}
	}

	return nil
}

// Index returns number from 0 to 1 where 0 means least loaded and 1 maximally loaded.
// It uses history of last 72 hours
func (p *Processor) Index() (*Node, error) {
	node := Node{
		Index: 1.0,
	}

	// Number of CPUs
	cpus, err := cpu.Counts(true)
	if err != nil {
		return &node, err
	}

	logs := []PerformanceLog{}

	err = p.DB.Find(&logs).Error
	if err != nil {
		return &node, err
	}

	var totalLoad1 float64
	var totalLoad5 float64
	var totalLoad15 float64
	var totalDiskSpaceUsage float64
	var totalMemory float64

	// If there is no record we have to wait until it is, until then the server is "full"
	if len(logs) == 0 {
		return &node, nil
	}

	for _, log := range logs {
		totalLoad1 += log.Load1
		totalLoad5 += log.Load5
		totalLoad15 += log.Load15
		totalDiskSpaceUsage += log.DiskSpaceUsage
		totalMemory += log.Memory
	}

	node.Load1Index = totalLoad1 / float64(len(logs)) / float64(cpus)
	node.Load5Index = totalLoad5 / float64(len(logs)) / float64(cpus)
	node.Load15Index = totalLoad15 / float64(len(logs)) / float64(cpus)
	node.MemoryIndex = totalMemory / float64(len(logs))
	node.DiskSpaceIndex = totalDiskSpaceUsage / float64(len(logs))

	var indexes []float64
	indexes = append(indexes, node.Load5Index)
	indexes = append(indexes, node.MemoryIndex)
	indexes = append(indexes, node.DiskSpaceIndex)

	finalIndex := float64(0)
	for _, index := range indexes {
		if index > finalIndex {
			finalIndex = index
		}
	}

	node.Index = finalIndex

	return &node, nil
}