package fileops

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

// RemoveAllUnderRoot removes target and its contents only after opening root and
// every target ancestor without following symbolic links. target must name a
// proper descendant of root. Symlinks are rejected rather than followed or
// removed so a failed cleanup never silently changes its scope.
func RemoveAllUnderRoot(rootPath, target string) error {
	root, targetName, err := openConfinedCleanupTarget(rootPath, target)
	if err != nil {
		return err
	}
	defer func() { _ = root.Close() }()
	return removeConfinedEntry(root, targetName)
}

func openConfinedCleanupTarget(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)
	}
	parts, err := relativePathParts(relative)
	if err != nil {
		return nil, "", err
	}
	root, err := openConfinedDirectory(rootAbs)
	if err != nil {
		return nil, "", err
	}
	for _, part := range parts[:len(parts)-1] {
		child, err := openConfinedChild(root, part, false, 0)
		if err != nil {
			_ = root.Close()
			return nil, "", err
		}
		_ = root.Close()
		root = child
	}
	return root, parts[len(parts)-1], nil
}

func openConfinedDirectory(path string) (*os.Root, error) {
	abs, err := filepath.Abs(path)
	if err != nil {
		return nil, fmt.Errorf("resolve directory: %w", err)
	}
	parts, err := absolutePathParts(abs)
	if err != nil {
		return nil, err
	}
	rootPath := filesystemRoot(abs)
	root, err := os.OpenRoot(rootPath)
	if err != nil {
		return nil, fmt.Errorf("open filesystem root %q: %w", rootPath, err)
	}
	for _, part := range parts {
		child, err := openConfinedChild(root, part, false, 0)
		if err != nil {
			_ = root.Close()
			return nil, err
		}
		_ = root.Close()
		root = child
	}
	return root, nil
}

func relativePathParts(path string) ([]string, error) {
	parts := strings.FieldsFunc(path, func(r rune) bool { return r == filepath.Separator || r == '/' || r == '\\' })
	if len(parts) == 0 {
		return nil, fmt.Errorf("cleanup target is required")
	}
	for _, part := range parts {
		if part == "" || part == "." || part == ".." {
			return nil, fmt.Errorf("unsafe cleanup path component %q", part)
		}
	}
	return parts, nil
}

func removeConfinedEntry(parent *os.Root, name string) error {
	info, err := parent.Lstat(name)
	if errors.Is(err, os.ErrNotExist) {
		return nil
	}
	if err != nil {
		return fmt.Errorf("inspect cleanup entry %q: %w", name, err)
	}
	if info.Mode()&os.ModeSymlink != 0 {
		return fmt.Errorf("refusing to delete symlink path %q", name)
	}
	if !info.IsDir() {
		if err := parent.Remove(name); err != nil {
			return fmt.Errorf("remove cleanup entry %q: %w", name, err)
		}
		return nil
	}

	child, err := openConfinedChild(parent, name, false, 0)
	if err != nil {
		return err
	}
	err = removeConfinedChildren(child)
	closeErr := child.Close()
	if err != nil {
		if closeErr != nil {
			return errors.Join(err, closeErr)
		}
		return err
	}
	if closeErr != nil {
		return fmt.Errorf("close cleanup directory %q: %w", name, closeErr)
	}
	if err := parent.Remove(name); err != nil {
		return fmt.Errorf("remove cleanup directory %q: %w", name, err)
	}
	return nil
}

func removeConfinedChildren(root *os.Root) error {
	directory, err := root.Open(".")
	if err != nil {
		return fmt.Errorf("open cleanup directory: %w", err)
	}
	entries, readErr := directory.ReadDir(-1)
	closeErr := directory.Close()
	if readErr != nil {
		return fmt.Errorf("read cleanup directory: %w", readErr)
	}
	if closeErr != nil {
		return fmt.Errorf("close cleanup directory: %w", closeErr)
	}
	sort.Slice(entries, func(i, j int) bool { return entries[i].Name() < entries[j].Name() })
	for _, entry := range entries {
		if err := removeConfinedEntry(root, entry.Name()); err != nil {
			return err
		}
	}
	return nil
}