package meminfo

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

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

const meminfoFileLocation = "/proc/meminfo"

var meminfoRegex = regexp.MustCompile(`(?m)^(?P<key>\S+):\s+(?P<value>\d+(?:\s\S+$|$))`)

func valueInBytes(rawVal string) (int, error) {
	split := strings.Split(rawVal, " ")

	baseVal, err := strconv.ParseInt(split[0], 10, 64)
	if err != nil {
		return 0, fmt.Errorf("invalid base value %q: %w", split[0], err)
	}

	if len(split) == 1 { // no unit present in the value
		return int(baseVal), nil
	}

	switch split[1] {
	case "B":
		return int(baseVal), nil
	case "kB":
		return 1000 * int(baseVal), nil
	case "MB":
		return 1_000_000 * int(baseVal), nil
	case "GB":
		return 1_000_000_000 * int(baseVal), nil
	case "TB":
		return 1_000_000_000_000 * int(baseVal), nil
	default:
		return 0, fmt.Errorf("invalid unit %q", split[1])
	}
}

type MeminfoCollector struct {
	meminfoFileLocation string

	promExporter *prometheus.SummaryVec
	updateFreq   time.Duration
}

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

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

	rawMatches, err := utils.HandleRegexp(string(fileContent), *meminfoRegex)
	if err != nil {
		return fmt.Errorf("failed to parse meminfo file: %w", err)
	}

	mappedVals := utils.HandleKeyValRegexRes(rawMatches)
	for valueType, rawVal := range mappedVals {
		val, err := valueInBytes(rawVal)
		if err != nil {
			return fmt.Errorf("invalid value in meminfo file: %w", err)
		}
		c.promExporter.WithLabelValues(valueType).Observe(float64(val))
	}

	return nil
}

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

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

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

func New() *MeminfoCollector {
	return &MeminfoCollector{
		updateFreq:          1 * time.Second,
		meminfoFileLocation: meminfoFileLocation,
		promExporter:        prometheus.NewSummaryVec(prometheus.SummaryOpts{Namespace: "system", Name: "meminfo", Help: "System memory info"}, []string{"type"}),
	}
}

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