package builder

import (
	"fmt"
	"os"
	"path/filepath"
	"syscall"
)

// FreeSpaceFloor is the free space a build node must have, on / and on its workspace's filesystem, before it takes
// a build or a check (novox/hq issue 1834): under it, a throwaway store cannot initialise its data directory and
// dies at once, and the check ended "never became ready" instead of saying the disk was full.
const FreeSpaceFloor = 20 << 30

// FreeBytes reads the bytes an unprivileged writer can still use on the filesystem holding path. A variable so a
// test answers for a disk it does not have.
var FreeBytes = func(path string) (uint64, error) {
	var s syscall.Statfs_t
	if err := syscall.Statfs(path, &s); err != nil {
		return 0, err
	}
	return s.Bavail * uint64(s.Bsize), nil
}

// RoomToWork refuses, saying how much is free, when any of the paths' filesystems is under FreeSpaceFloor. A path
// that does not exist yet (a workspace not made) is read at its nearest folder that does.
func RoomToWork(paths ...string) error {
	for _, p := range paths {
		at := p
		for {
			if _, err := os.Stat(at); err == nil || filepath.Dir(at) == at {
				break
			}
			at = filepath.Dir(at)
		}
		free, err := FreeBytes(at)
		if err != nil {
			return fmt.Errorf("the free space on %s cannot be read: %w", p, err)
		}
		if free < FreeSpaceFloor {
			return fmt.Errorf("the build node has %d GiB free on %s, under the floor of %d GiB",
				free>>30, p, FreeSpaceFloor>>30)
		}
	}
	return nil
}