package fileops

import (
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strings"
)

// RemoveAllUnderRoot removes target and its contents beneath root. target must
// name a proper descendant of root; removal is confined by the opened root.
func RemoveAllUnderRoot(rootPath, target string) error {
	root, targetName, err := openCleanupRoot(rootPath, target)
	if err != nil {
		return err
	}
	defer func() { _ = root.Close() }()
	if err := root.RemoveAll(targetName); err != nil {
		return fmt.Errorf("remove cleanup target %q: %w", targetName, err)
	}
	return nil
}

// RemoveFileUnderRoot removes an exact regular-file target below root without
// following the leaf. A missing target is successful; directories, symlinks,
// and other non-regular entries are rejected.
func RemoveFileUnderRoot(rootPath, target string) error {
	root, targetName, err := openCleanupRoot(rootPath, target)
	if err != nil {
		return err
	}
	defer func() { _ = root.Close() }()

	info, err := root.Lstat(targetName)
	if errors.Is(err, os.ErrNotExist) {
		return nil
	}
	if err != nil {
		return fmt.Errorf("inspect cleanup file %q: %w", targetName, err)
	}
	if !info.Mode().IsRegular() {
		return fmt.Errorf("refusing to delete non-regular file path %q", targetName)
	}
	if err := root.Remove(targetName); err != nil {
		return fmt.Errorf("remove cleanup file %q: %w", targetName, err)
	}
	return nil
}

func openCleanupRoot(rootPath, target string) (*os.Root, string, error) {
	if strings.TrimSpace(rootPath) == "" {
		return nil, "", fmt.Errorf("cleanup root is required")
	}
	if strings.TrimSpace(target) == "" {
		return nil, "", fmt.Errorf("cleanup target is required")
	}
	rootAbs, err := filepath.Abs(rootPath)
	if err != nil {
		return nil, "", fmt.Errorf("resolve cleanup root: %w", err)
	}
	targetAbs, err := filepath.Abs(target)
	if err != nil {
		return nil, "", fmt.Errorf("resolve cleanup target: %w", err)
	}
	relative, err := filepath.Rel(rootAbs, targetAbs)
	if err != nil {
		return nil, "", fmt.Errorf("resolve cleanup target below root: %w", err)
	}
	if relative == "." || relative == ".." || strings.HasPrefix(relative, ".."+string(filepath.Separator)) {
		return nil, "", fmt.Errorf("cleanup target %q must be below root %q", targetAbs, rootAbs)
	}
	name := filepath.Clean(relative)
	if filepath.IsAbs(name) || name == "." || name == ".." || strings.HasPrefix(name, ".."+string(filepath.Separator)) {
		return nil, "", fmt.Errorf("cleanup target %q must be below root %q", targetAbs, rootAbs)
	}
	root, err := os.OpenRoot(rootAbs)
	if err != nil {
		return nil, "", fmt.Errorf("open cleanup root %q: %w", rootAbs, err)
	}
	return root, name, nil
}