//go:build !windows

package safeio

import (
	"os"
	"strings"

	"golang.org/x/sys/unix"
)

// ReadCanonicalRegular opens an absolute canonical path component by component from the root
// descriptor. O_NOFOLLOW rejects symlinks at every component, and the open directory descriptors
// prevent later parent replacement from redirecting the final open.
func ReadCanonicalRegular(path string, maximum int64) ([]byte, error) {
	if err := ValidateCanonicalPath(path); err != nil {
		return nil, err
	}
	components := strings.Split(strings.TrimPrefix(path, string(os.PathSeparator)), string(os.PathSeparator))
	if len(components) == 0 || components[0] == "" {
		return nil, ErrUnsafeFile
	}

	directory, err := unix.Open(string(os.PathSeparator), unix.O_RDONLY|unix.O_CLOEXEC|unix.O_DIRECTORY, 0)
	if err != nil {
		return nil, ErrUnsafeFile
	}
	directories := []int{directory}
	defer func() { closeUnixDescriptors(directories) }()

	for _, component := range components[:len(components)-1] {
		nextDirectory, err := unix.Openat(directory, component, unix.O_RDONLY|unix.O_CLOEXEC|unix.O_DIRECTORY|unix.O_NOFOLLOW, 0)
		if err != nil {
			return nil, ErrUnsafeFile
		}
		directory = nextDirectory
		directories = append(directories, directory)
	}

	descriptor, err := unix.Openat(directory, components[len(components)-1], unix.O_RDONLY|unix.O_CLOEXEC|unix.O_NOFOLLOW|unix.O_NONBLOCK, 0)
	if err != nil {
		return nil, ErrUnsafeFile
	}
	file := os.NewFile(uintptr(descriptor), "thothctl-safeio")
	if file == nil {
		unix.Close(descriptor)
		return nil, ErrUnsafeFile
	}
	defer file.Close()
	return readBoundedRegularFile(path, file, maximum)
}

func closeUnixDescriptors(descriptors []int) {
	for _, descriptor := range descriptors {
		unix.Close(descriptor)
	}
}