package discovery

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

// MemoryTotalMB reports the machine's total RAM.
//
// It exists because placement had no idea how much a node could hold. A CPU
// profile has no card to be free, so every ready node looked like a candidate:
// a 14B model whose working set is 24 GB would have been placed just as
// happily on a node with 8 GB, which reports itself perfectly healthy right up
// until the OOM killer arrives. Labels were the stopgap; this is the fact they
// were standing in for.
//
// Read from /proc/meminfo, which is Linux-only — every node is. On anything
// else it returns 0, which callers treat as "unknown" and therefore no
// constraint, exactly as an older agent that does not report it at all.
func MemoryTotalMB() int { return memTotalMBFrom("/proc/meminfo") }

func memTotalMBFrom(path string) int {
	f, err := os.Open(path)
	if err != nil {
		return 0
	}
	defer f.Close()

	sc := bufio.NewScanner(f)
	for sc.Scan() {
		rest, ok := strings.CutPrefix(sc.Text(), "MemTotal:")
		if !ok {
			continue
		}
		fields := strings.Fields(rest)
		if len(fields) == 0 {
			return 0
		}
		kb, err := strconv.Atoi(fields[0])
		if err != nil {
			return 0
		}
		// MemTotal is what the kernel can hand out, already short of the
		// installed total by the firmware's reservations. That is the right
		// number for deciding what fits.
		return kb / 1024
	}
	return 0
}