package uptime

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

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

const procUptimeLocation = "/proc/uptime"

type UptimeCollector struct {
	ctx              context.Context
	procFileLocation string
	uptimeFreq       time.Duration
	uptime           time.Duration
	uptimeProm       prometheus.Gauge
}

func (c *UptimeCollector) Collect() interface{} {
	return c.uptime
}

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

	uptimeVals := strings.Split(string(fileContent), " ")
	if len(uptimeVals) != 2 {
		return fmt.Errorf("invalid format for /proc/uptime: %q", string(fileContent))
	}

	uptimeFloat, err := strconv.ParseFloat(uptimeVals[0], 64)
	if err != nil {
		return fmt.Errorf("invalid uptime format for float %s: %w", uptimeVals[0], err)
	}

	c.uptime = time.Duration(int(uptimeFloat)) * time.Second
	c.uptimeProm.Set(uptimeFloat)
	return nil
}

func (c *UptimeCollector) PromCollector() prometheus.Collector {
	return c.uptimeProm
}

func (c *UptimeCollector) Run(ctx context.Context) {
	if err := c.update(); err != nil {
		fmt.Printf("Failed to init collector: %s\n", err)
	}

	for {
		select {
		case <-ctx.Done():
			return
		case <-time.After(c.uptimeFreq):
			if err := c.update(); err != nil {
				fmt.Printf("Failed to update collector: %s\n", err)
			}
		}
	}
}

func New() *UptimeCollector {
	return &UptimeCollector{
		ctx:              context.TODO(),
		procFileLocation: procUptimeLocation,
		uptimeFreq:       1 * time.Second,
		uptime:           0,
		uptimeProm:       prometheus.NewGauge(prometheus.GaugeOpts{Namespace: "system", Name: "uptime_nanosec", Help: "System uptime in nanoseconds"}),
	}

}

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