package hostcollect

import (
	"fmt"
	"strings"

	"github.com/itworx/pulse/internal/host"
)

// parseMeminfo converts /proc/meminfo into bytes.
//
// meminfo is kB based ("MemTotal: 16316420 kB"), where kB means KiB, and a handful of
// counters carry no unit at all. Treating either as bytes is the classic off-by-1024
// bug, so the unit is read per line instead of assumed.
func parseMeminfo(data []byte) (host.RawMemory, error) {
	values := make(map[string]uint64, 8)
	for _, line := range lines(data) {
		key, rest, found := strings.Cut(line, ":")
		if !found {
			continue
		}
		fields := strings.Fields(rest)
		if len(fields) == 0 {
			continue
		}
		amount, ok := parseUint(fields[0])
		if !ok {
			continue
		}
		if len(fields) > 1 && strings.EqualFold(fields[1], "kB") {
			const kib = 1024
			if amount > (1<<64-1)/kib {
				continue
			}
			amount *= kib
		}
		values[strings.TrimSpace(key)] = amount
	}
	total := values["MemTotal"]
	if total == 0 {
		return host.RawMemory{}, errNoMemTotal
	}
	available, ok := values["MemAvailable"]
	if !ok {
		// Kernels before 3.14 have no MemAvailable. The traditional approximation is
		// free plus the reclaimable page cache; it is an estimate, never above total.
		available = values["MemFree"] + values["Buffers"] + values["Cached"] + values["SReclaimable"]
	}
	if available > total {
		available = total
	}
	memory := host.RawMemory{TotalBytes: total, AvailableBytes: available}
	swapTotal := values["SwapTotal"]
	if swapTotal > 0 {
		swapFree := values["SwapFree"]
		if swapFree > swapTotal {
			swapFree = swapTotal
		}
		memory.SwapTotalBytes = swapTotal
		memory.SwapUsedBytes = swapTotal - swapFree
	}
	return memory, nil
}

func (c *Collector) memory() (host.RawMemory, error) {
	data, err := readLimited(c.procPath("meminfo"), maxFileBytes)
	if err != nil {
		return host.RawMemory{}, fmt.Errorf("hostcollect: read meminfo: %w", err)
	}
	return parseMeminfo(data)
}