package host

import (
	"strconv"
	"strings"

	"github.com/carlosframework/platform/internal/registry"
)

// headroomFor is the reading the edges loop publishes: nil unless the box
// has the region-HA capability. A box that publishes headroom is rewritten
// on every timed pass, so a one-box region (flag off) must not carry one.
func headroomFor(caps []string, dataDir string, reg *registry.Registry) *edgeHeadroom {
	if len(caps) == 0 {
		return nil
	}
	h := readHeadroom(dataDir, awakeCount(reg))
	h.MemTotalMiB, h.DiskTotalMiB = capacityMiB(readMemBytes, func() (uint64, uint64, error) { return diskBytes(dataDir) })
	return h
}

// capacityMiB is the box's total memory and its data volume's size, in
// MiB: the totals region HA spec 2's placement policy judges the free
// figures against (§7). A reading that fails is 0, which the policy reads
// as a box it cannot judge, and so does not place on.
func capacityMiB(mem func() (total, avail *int64), disk func() (total, avail uint64, err error)) (memMiB, diskMiB int64) {
	if total, _ := mem(); total != nil && *total > 0 {
		memMiB = *total / (1 << 20)
	}
	if total, _, err := disk(); err == nil {
		diskMiB = int64(total / (1 << 20))
	}
	return memMiB, diskMiB
}

// parseMemAvailableMiB returns the MemAvailable line in MiB, or 0.
func parseMemAvailableMiB(meminfo string) int64 {
	for _, line := range strings.Split(meminfo, "\n") {
		rest, ok := strings.CutPrefix(line, "MemAvailable:")
		if !ok {
			continue
		}
		fields := strings.Fields(rest)
		if len(fields) == 0 {
			return 0
		}
		kb, err := strconv.ParseInt(fields[0], 10, 64)
		if err != nil {
			return 0
		}
		return kb / 1024
	}
	return 0
}