package stats

import (
	"time"

	"github.com/shirou/gopsutil/cpu"
	"github.com/shirou/gopsutil/disk"
	"github.com/shirou/gopsutil/host"
	"github.com/shirou/gopsutil/mem"
)

// HostStats represents resource usage stats of the host running a Nomad client
type HostStats struct {
	Memory    *MemoryStats
	CPU       []*CPUStats
	DiskStats []*DiskStats
	Uptime    uint64
	Timestamp int64
}

// MemoryStats represnts stats related to virtual memory usage
type MemoryStats struct {
	Total     uint64
	Available uint64
	Used      uint64
	Free      uint64
}

// CPUStats represents stats related to cpu usage
type CPUStats struct {
	CPU    string
	User   float64
	System float64
	Idle   float64
	Total  float64
}

// DiskStats represents stats related to disk usage
type DiskStats struct {
	Device            string
	Mountpoint        string
	Size              uint64
	Used              uint64
	Available         uint64
	UsedPercent       float64
	InodesUsedPercent float64
}

// HostStatsCollector collects host resource usage stats
type HostStatsCollector struct {
	statsCalculator map[string]*HostCpuStatsCalculator
}

// NewHostStatsCollector returns a HostStatsCollector
func NewHostStatsCollector() *HostStatsCollector {
	statsCalculator := make(map[string]*HostCpuStatsCalculator)
	return &HostStatsCollector{statsCalculator: statsCalculator}
}

// Collect collects stats related to resource usage of a host
func (h *HostStatsCollector) Collect() (*HostStats, error) {
	hs := &HostStats{Timestamp: time.Now().UTC().UnixNano()}
	if memStats, err := mem.VirtualMemory(); err == nil {
		ms := &MemoryStats{
			Total:     memStats.Total,
			Available: memStats.Available,
			Used:      memStats.Used,
			Free:      memStats.Free,
		}
		hs.Memory = ms
	}

	if cpuStats, err := cpu.Times(true); err == nil {
		cs := make([]*CPUStats, len(cpuStats))
		for idx, cpuStat := range cpuStats {
			cs[idx] = &CPUStats{
				CPU:    cpuStat.CPU,
				User:   cpuStat.User,
				System: cpuStat.System,
				Idle:   cpuStat.Idle,
			}
			percentCalculator, ok := h.statsCalculator[cpuStat.CPU]
			if !ok {
				percentCalculator = NewHostCpuStatsCalculator()
				h.statsCalculator[cpuStat.CPU] = percentCalculator
			}
			idle, user, system, total := percentCalculator.Calculate(cpuStat)
			cs[idx].Idle = idle
			cs[idx].System = system
			cs[idx].User = user
			cs[idx].Total = total
		}
		hs.CPU = cs
	}

	if partitions, err := disk.Partitions(false); err == nil {
		var diskStats []*DiskStats
		for _, partition := range partitions {
			if usage, err := disk.Usage(partition.Mountpoint); err == nil {
				ds := DiskStats{
					Device:            partition.Device,
					Mountpoint:        partition.Mountpoint,
					Size:              usage.Total,
					Used:              usage.Used,
					Available:         usage.Free,
					UsedPercent:       usage.UsedPercent,
					InodesUsedPercent: usage.InodesUsedPercent,
				}
				diskStats = append(diskStats, &ds)
			}
		}
		hs.DiskStats = diskStats
	}

	if uptime, err := host.Uptime(); err == nil {
		hs.Uptime = uptime
	}
	return hs, nil
}

// HostCpuStatsCalculator calculates cpu usage percentages
type HostCpuStatsCalculator struct {
	prevIdle   float64
	prevUser   float64
	prevSystem float64
	prevBusy   float64
	prevTotal  float64
}

// NewHostCpuStatsCalculator returns a HostCpuStatsCalculator
func NewHostCpuStatsCalculator() *HostCpuStatsCalculator {
	return &HostCpuStatsCalculator{}
}

// Calculate calculates the current cpu usage percentages
func (h *HostCpuStatsCalculator) Calculate(times cpu.TimesStat) (idle float64, user float64, system float64, total float64) {
	currentIdle := times.Idle
	currentUser := times.User
	currentSystem := times.System
	currentTotal := times.Total()

	deltaTotal := currentTotal - h.prevTotal
	idle = ((currentIdle - h.prevIdle) / deltaTotal) * 100
	user = ((currentUser - h.prevUser) / deltaTotal) * 100
	system = ((currentSystem - h.prevSystem) / deltaTotal) * 100

	currentBusy := times.User + times.System + times.Nice + times.Iowait + times.Irq +
		times.Softirq + times.Steal + times.Guest + times.GuestNice + times.Stolen

	total = ((currentBusy - h.prevBusy) / deltaTotal) * 100

	h.prevIdle = currentIdle
	h.prevUser = currentUser
	h.prevSystem = currentSystem
	h.prevTotal = currentTotal
	h.prevBusy = currentBusy

	return
}