package diskspace

import (
	"errors"
	"fmt"
	"math"
	"syscall"
)

var ErrInsufficientSpace = errors.New("not enough free disk space")

func Available(path string) (int64, error) {
	var stats syscall.Statfs_t
	if err := syscall.Statfs(path, &stats); err != nil {
		return 0, err
	}
	available := stats.Bavail * uint64(stats.Bsize)
	if available > math.MaxInt64 {
		return math.MaxInt64, nil
	}
	return int64(available), nil
}

func EnsureFree(path string, requiredBytes, reservedBytes int64) error {
	available, err := Available(path)
	if err != nil {
		return err
	}
	if available-reservedBytes < requiredBytes {
		return fmt.Errorf("%w: %.1f GiB needed, %.1f GiB usable after keeping %.1f GiB free",
			ErrInsufficientSpace, toGiB(requiredBytes), toGiB(available-reservedBytes), toGiB(reservedBytes))
	}
	return nil
}

func toGiB(bytes int64) float64 {
	return float64(bytes) / float64(1<<30)
}