//go:build !unix

package promptdebug

import (
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
)

type secureDirectory struct {
	root *os.Root
}

func openSecureDirectory(path string) (*secureDirectory, error) {
	if !filepath.IsAbs(path) {
		return nil, fmt.Errorf("directory must be absolute")
	}
	if err := os.MkdirAll(path, debugDirectoryMode); err != nil {
		return nil, err
	}
	info, err := os.Lstat(path)
	if err != nil {
		return nil, err
	}
	if info.Mode()&os.ModeSymlink != 0 || !info.IsDir() {
		return nil, fmt.Errorf("prompt debug root is not a directory")
	}
	if err := os.Chmod(path, debugDirectoryMode); err != nil {
		return nil, err
	}
	root, err := os.OpenRoot(path)
	if err != nil {
		return nil, err
	}
	return &secureDirectory{root: root}, nil
}

func (directory *secureDirectory) Close() error {
	if directory == nil || directory.root == nil {
		return nil
	}
	root := directory.root
	directory.root = nil
	return root.Close()
}

func (directory *secureDirectory) openDirectory(components ...string) (*secureDirectory, error) {
	if directory == nil || directory.root == nil {
		return nil, fmt.Errorf("prompt debug directory is closed")
	}
	for _, component := range components {
		if err := validateSecureDirectoryName(component); err != nil {
			return nil, err
		}
	}
	path := filepath.Join(components...)
	if err := directory.root.MkdirAll(path, debugDirectoryMode); err != nil {
		return nil, err
	}
	child, err := directory.root.OpenRoot(path)
	if err != nil {
		return nil, err
	}
	return &secureDirectory{root: child}, nil
}

func validateSecureDirectoryName(name string) error {
	if name == "" || name == "." || name == ".." || strings.ContainsRune(name, filepath.Separator) {
		return fmt.Errorf("prompt debug directory component %q is invalid", name)
	}
	return nil
}

func (directory *secureDirectory) writeJSON(name string, value any) error {
	if directory == nil || directory.root == nil {
		return fmt.Errorf("prompt debug directory is closed")
	}
	if err := validateSecureDirectoryName(name); err != nil {
		return err
	}
	data, err := json.MarshalIndent(value, "", "  ")
	if err != nil {
		return fmt.Errorf("marshal prompt debug artifact: %w", err)
	}
	if info, err := directory.root.Lstat(name); err == nil {
		if info.Mode()&os.ModeSymlink != 0 || !info.Mode().IsRegular() {
			return fmt.Errorf("prompt debug file %q is not a regular file", name)
		}
	} else if !os.IsNotExist(err) {
		return err
	}
	temporaryName, temporary, err := directory.createTemporaryFile(name)
	if err != nil {
		return err
	}
	defer func() {
		if temporary != nil {
			_ = temporary.Close()
		}
		_ = directory.root.Remove(temporaryName)
	}()
	if err := temporary.Chmod(debugFileMode); err != nil {
		return err
	}
	if written, err := temporary.Write(data); err != nil {
		return err
	} else if written != len(data) {
		return io.ErrShortWrite
	}
	if err := temporary.Close(); err != nil {
		return err
	}
	temporary = nil
	if err := directory.root.Rename(temporaryName, name); err != nil {
		return fmt.Errorf("replace prompt debug file %q: %w", name, err)
	}
	return nil
}

func (directory *secureDirectory) createTemporaryFile(name string) (string, *os.File, error) {
	for attempt := 0; attempt < 16; attempt++ {
		random := make([]byte, 12)
		if _, err := rand.Read(random); err != nil {
			return "", nil, err
		}
		temporaryName := "." + name + "." + hex.EncodeToString(random) + ".tmp"
		temporary, err := directory.root.OpenFile(temporaryName, os.O_WRONLY|os.O_CREATE|os.O_EXCL, debugFileMode)
		if os.IsExist(err) {
			continue
		}
		if err != nil {
			return "", nil, err
		}
		return temporaryName, temporary, nil
	}
	return "", nil, fmt.Errorf("create temporary prompt debug file: too many name collisions")
}