//go:build unix

package hostfiles

import (
	"context"
	"errors"

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

// syncTree walks the tree beneath root by descriptor and calls visit for
// every entry that is not a directory, with the open directory that holds
// it, its name there, and its path relative to root. It never follows a
// symlink and never blocks on a FIFO: a directory is entered only through
// openDir.
//
// The walk is bounded (withinTreeCap): a path past MaxPathBytes refuses
// the whole walk with ErrTooDeep, never a
// silent skip, so a tree no restore could recreate is never published as
// complete, and a chain of directories cannot make the walk's memory grow
// with the square of its depth. ctx is checked on entering every
// directory, so a deep tree with no files still stops when cancelled.
func syncTree(ctx context.Context, root *dirHandle, p *Publisher, skip func(string, bool) bool, visit func(d *dirHandle, name, rel string) error) error {
	return walkDir(ctx, root, "", skip, visit)
}

func walkDir(ctx context.Context, d *dirHandle, prefix string, skip func(string, bool) bool, visit func(d *dirHandle, name, rel string) error) error {
	if err := ctx.Err(); err != nil {
		return err
	}
	names, err := d.names()
	if err != nil {
		return err
	}
	for _, name := range names {
		rel := name
		if prefix != "" {
			rel = prefix + "/" + name
		}
		st, err := d.look(name)
		if errors.Is(err, unix.ENOENT) {
			continue
		}
		if err != nil {
			return err
		}
		if !isDir(st) {
			if skipped(skip, rel, false) {
				continue
			}
			if err := withinTreeCap(rel); err != nil {
				return err
			}
			if err := visit(d, name, rel); err != nil {
				return err
			}
			continue
		}
		if skipped(skip, rel, true) {
			continue
		}
		if err := withinTreeCap(rel); err != nil {
			return err
		}
		betweenLookAndOpen()
		sub, err := d.openDir(name)
		if err != nil {
			if errors.Is(err, unix.ENOENT) {
				continue
			}
			if notADirectory(err) {
				// It was a directory a moment ago and is something else
				// now. Let readStable say what: it will not follow or
				// block on it either.
				if err := visit(d, name, rel); err != nil {
					return err
				}
				continue
			}
			return err
		}
		err = walkDir(ctx, sub, rel, skip, visit)
		sub.Close()
		if err != nil {
			return err
		}
	}
	return nil
}