package nvidia_smi

import (
	"bufio"
	"fmt"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"time"

	"github.com/influxdata/telegraf"
	"github.com/influxdata/telegraf/internal"
	"github.com/influxdata/telegraf/plugins/inputs"
)

var (
	measurement = "nvidia_smi"
	metrics     = "fan.speed,memory.total,memory.used,memory.free,pstate,temperature.gpu,name,uuid,compute_mode,utilization.gpu,utilization.memory,index"
	metricNames = [][]string{
		[]string{"fan_speed", "field"},
		[]string{"memory_total", "field"},
		[]string{"memory_used", "field"},
		[]string{"memory_free", "field"},
		[]string{"pstate", "tag"},
		[]string{"temperature_gpu", "field"},
		[]string{"name", "tag"},
		[]string{"uuid", "tag"},
		[]string{"compute_mode", "tag"},
		[]string{"utilization_gpu", "field"},
		[]string{"utilization_memory", "field"},
		[]string{"index", "tag"},
	}
)

// NvidiaSMI holds the methods for this plugin
type NvidiaSMI struct {
	BinPath string
	Timeout time.Duration

	metrics string
}

// Description returns the description of the NvidiaSMI plugin
func (smi *NvidiaSMI) Description() string {
	return "Pulls statistics from nvidia GPUs attached to the host"
}

// SampleConfig returns the sample configuration for the NvidiaSMI plugin
func (smi *NvidiaSMI) SampleConfig() string {
	return `
## Optional: path to nvidia-smi binary, defaults to $PATH via exec.LookPath
# bin_path = /usr/bin/nvidia-smi

## Optional: timeout for GPU polling
# timeout = 5s
`
}

// Gather implements the telegraf interface
func (smi *NvidiaSMI) Gather(acc telegraf.Accumulator) error {

	if _, err := os.Stat(smi.BinPath); os.IsNotExist(err) {
		return fmt.Errorf("nvidia-smi binary not at path %s, cannot gather GPU data", smi.BinPath)
	}

	data, err := smi.pollSMI()
	if err != nil {
		return err
	}

	err = gatherNvidiaSMI(data, acc)
	if err != nil {
		return err
	}

	return nil
}

func init() {
	inputs.Add("nvidia_smi", func() telegraf.Input {
		return &NvidiaSMI{
			BinPath: "/usr/bin/nvidia-smi",
			Timeout: 5 * time.Second,
			metrics: metrics,
		}
	})
}

func (smi *NvidiaSMI) pollSMI() (string, error) {
	// Construct and execute metrics query
	opts := []string{"--format=noheader,nounits,csv", fmt.Sprintf("--query-gpu=%s", smi.metrics)}
	ret, err := internal.CombinedOutputTimeout(exec.Command(smi.BinPath, opts...), smi.Timeout)
	if err != nil {
		return "", err
	}
	return string(ret), nil
}

func gatherNvidiaSMI(ret string, acc telegraf.Accumulator) error {
	// First split the lines up and handle each one
	scanner := bufio.NewScanner(strings.NewReader(ret))
	for scanner.Scan() {
		tags, fields, err := parseLine(scanner.Text())
		if err != nil {
			return err
		}
		acc.AddFields(measurement, fields, tags)
	}

	if err := scanner.Err(); err != nil {
		return fmt.Errorf("Error scanning text %s", ret)
	}

	return nil
}

func parseLine(line string) (map[string]string, map[string]interface{}, error) {
	tags := make(map[string]string, 0)
	fields := make(map[string]interface{}, 0)

	// Next split up the comma delimited metrics
	met := strings.Split(line, ",")

	// Make sure there are as many metrics in the line as there were queried.
	if len(met) == len(metricNames) {
		for i, m := range metricNames {

			// First handle the tags
			if m[1] == "tag" {
				tags[m[0]] = strings.TrimSpace(met[i])
				continue
			}

			// Then parse the integers out of the fields
			out, err := strconv.ParseInt(strings.TrimSpace(met[i]), 10, 64)
			if err != nil {
				return tags, fields, err
			}
			fields[m[0]] = out
		}

		// Return the tags and fields
		return tags, fields, nil
	}

	// If the line is empty return an emptyline error
	return tags, fields, fmt.Errorf("Different number of metrics returned (%d) than expeced (%d)", len(met), len(metricNames))
}