package loadavg

import (
	"context"
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"

	"git.faercol.me/monitoring/sys-exporter/registry"
	"github.com/prometheus/client_golang/prometheus"
	"go.uber.org/zap"
)

const loadAvgFileLocation = "/proc/loadavg"

type LoadAvgCollector struct {
	loadAvgFileLocation string
	promExporter        *prometheus.SummaryVec
	updateFreq          time.Duration
	l                   *zap.SugaredLogger
}

func (c *LoadAvgCollector) Collect() interface{} {
	return nil
}

func (c *LoadAvgCollector) update() error {
	fileContent, err := os.ReadFile(c.loadAvgFileLocation)
	if err != nil {
		return fmt.Errorf("failed to read loadavg file: %w", err)
	}

	vals := strings.Split(string(fileContent), " ")
	if len(vals) != 5 {
		return fmt.Errorf("invalid format %q for loadavg file", string(fileContent))
	}

	var load1Min, load5Min, load15Min float64
	if load1Min, err = strconv.ParseFloat(vals[0], 64); err != nil {
		return fmt.Errorf("invalid value %q for load 1min: %w", vals[0], err)
	}
	if load5Min, err = strconv.ParseFloat(vals[1], 64); err != nil {
		return fmt.Errorf("invalid value %q for load 5mins: %w", vals[1], err)
	}
	if load15Min, err = strconv.ParseFloat(vals[2], 64); err != nil {
		return fmt.Errorf("invalid value %q for load 15min: %w", vals[2], err)
	}

	c.promExporter.WithLabelValues("1min").Observe(load1Min)
	c.promExporter.WithLabelValues("5mins").Observe(load5Min)
	c.promExporter.WithLabelValues("15mins").Observe(load15Min)
	return nil
}

func (c *LoadAvgCollector) Run(ctx context.Context, l *zap.SugaredLogger) {
	c.l = l

	c.l.Debug("Initializing collector")
	if err := c.update(); err != nil {
		c.l.Errorf("Failed to init collector: %s\n", err)
	}

	for {
		select {
		case <-ctx.Done():
			c.l.Debug("Stopping collector")
			return
		case <-time.After(c.updateFreq):
			c.l.Debug("Updating collector")
			if err := c.update(); err != nil {
				c.l.Errorf("Failed to update collector: %s\n", err)
			}
		}
	}
}

func (c *LoadAvgCollector) PromCollector() prometheus.Collector {
	return c.promExporter
}

func New() *LoadAvgCollector {
	return &LoadAvgCollector{
		updateFreq:          1 * time.Second,
		loadAvgFileLocation: loadAvgFileLocation,
		promExporter:        prometheus.NewSummaryVec(prometheus.SummaryOpts{Namespace: "system", Name: "loadavg", Help: "Load average of the system"}, []string{"period"}),
	}
}

func init() {
	registry.R.MustRegisterCollector("system.loadavg", New())
}