package collect

import (
	"bufio"
	"bytes"
	"os"
	"strconv"
	"strings"
)

type Memory struct {
	Total     uint64 `json:"total"`
	Available uint64 `json:"available"`
	Used      uint64 `json:"used"` // Total - Available
	SwapTotal uint64 `json:"swap_total"`
	SwapUsed  uint64 `json:"swap_used"`
	ARCSize   uint64 `json:"arc_size"`
	ARCMax    uint64 `json:"arc_max"`
}

func ReadMemory() (Memory, error) {
	b, err := os.ReadFile("/proc/meminfo")
	if err != nil {
		return Memory{}, err
	}
	m := parseMeminfo(b)
	if ab, err := os.ReadFile("/proc/spl/kstat/zfs/arcstats"); err == nil {
		m.ARCSize, m.ARCMax = parseArcstats(ab)
	}
	return m, nil
}

func parseMeminfo(b []byte) Memory {
	kv := map[string]uint64{}
	sc := bufio.NewScanner(bytes.NewReader(b))
	for sc.Scan() {
		f := strings.Fields(sc.Text())
		if len(f) < 2 {
			continue
		}
		n, err := strconv.ParseUint(f[1], 10, 64)
		if err != nil {
			continue
		}
		kv[strings.TrimSuffix(f[0], ":")] = n * 1024
	}
	m := Memory{
		Total:     kv["MemTotal"],
		Available: kv["MemAvailable"],
		SwapTotal: kv["SwapTotal"],
	}
	m.Used = m.Total - m.Available
	m.SwapUsed = m.SwapTotal - kv["SwapFree"]
	return m
}

// parseArcstats picks "size" and "c_max" from the kstat table (name type data).
func parseArcstats(b []byte) (size, max uint64) {
	sc := bufio.NewScanner(bytes.NewReader(b))
	for sc.Scan() {
		f := strings.Fields(sc.Text())
		if len(f) != 3 {
			continue
		}
		n, err := strconv.ParseUint(f[2], 10, 64)
		if err != nil {
			continue
		}
		switch f[0] {
		case "size":
			size = n
		case "c_max":
			max = n
		}
	}
	return
}