package storage

import (
	"errors"
	"fmt"
	"io"
	"io/fs"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"syscall"
	"time"

	"github.com/Bios-Marcel/wastebasket"
)

type Trashable interface {
	Trash(path string) error
	MoveToTrash(path, trashRoot string) error
}

type Storage interface {
	Stat(path string) (os.FileInfo, error)
	Open(path string) (*os.File, error)
	Create(path string) (*os.File, error)
	Remove(path string) error
	Rename(oldPath, newPath string) error
	MkdirAll(path string) error
	List(path string) ([]os.FileInfo, error)
}

type Local struct{ Root string }

func (s Local) real(path string) (string, error) {
	root, err := filepath.Abs(s.Root)
	if err != nil {
		return "", err
	}
	root, err = filepath.EvalSymlinks(root)
	if err != nil {
		return "", err
	}
	p := strings.TrimPrefix(filepath.Clean("/"+path), string(filepath.Separator))
	full := filepath.Join(root, p)
	rel, err := filepath.Rel(root, full)
	if err != nil {
		return "", err
	}
	if rel == ".." || strings.HasPrefix(rel, ".."+string(filepath.Separator)) {
		return "", errors.New("path escapes storage root")
	}
	check := full
	for {
		if _, err = os.Lstat(check); !os.IsNotExist(err) {
			break
		}
		next := filepath.Dir(check)
		if next == check {
			break
		}
		check = next
	}
	resolved, err := filepath.EvalSymlinks(check)
	if err != nil {
		return "", err
	}
	resolvedRel, err := filepath.Rel(root, resolved)
	if err != nil || resolvedRel == ".." || strings.HasPrefix(resolvedRel, ".."+string(filepath.Separator)) {
		return "", errors.New("path escapes storage root")
	}
	return full, nil
}
func (s Local) Stat(path string) (os.FileInfo, error) {
	p, e := s.real(path)
	if e != nil {
		return nil, e
	}
	return os.Stat(p)
}
func (s Local) Open(path string) (*os.File, error) {
	p, e := s.real(path)
	if e != nil {
		return nil, e
	}
	return os.Open(p)
}
func (s Local) Create(path string) (*os.File, error) {
	p, e := s.real(path)
	if e != nil {
		return nil, e
	}
	if e = os.MkdirAll(filepath.Dir(p), 0755); e != nil {
		return nil, e
	}
	return os.Create(p)
}
func (s Local) Remove(path string) error {
	p, e := s.real(path)
	if e != nil {
		return e
	}
	return os.RemoveAll(p)
}

func (s Local) Trash(path string) error {
	p, e := s.real(path)
	if e != nil {
		return e
	}
	return wastebasket.Trash(p)
}

func (s Local) MoveToTrash(path, trashRoot string) error {
	p, e := s.real(path)
	if e != nil {
		return e
	}
	root, e := filepath.Abs(s.Root)
	if e != nil {
		return e
	}
	rel, e := filepath.Rel(root, p)
	if e != nil || rel == ".." || strings.HasPrefix(rel, ".."+string(filepath.Separator)) {
		return errors.New("path escapes storage root")
	}
	if e = os.MkdirAll(trashRoot, 0755); e != nil {
		return e
	}
	// Preserve the original relative path under the CHFS trash root so
	// identically named files from different directories cannot collide.
	target := filepath.Join(trashRoot, rel)
	if e = os.MkdirAll(filepath.Dir(target), 0755); e != nil {
		return e
	}
	for i := 1; ; i++ {
		if _, e = os.Lstat(target); os.IsNotExist(e) {
			break
		}
		target = filepath.Join(filepath.Dir(target), fmt.Sprintf("%s.%d", filepath.Base(p), i))
	}
	if e = movePath(p, target); e != nil {
		return e
	}
	// Cleanup is maintenance work; a successful move must not be reported as
	// a failed delete merely because an unrelated stale trash entry is busy.
	_ = cleanupTrash(trashRoot, 30*24*time.Hour)
	return nil
}

func cleanupTrash(root string, maxAge time.Duration) error {
	now := time.Now()
	return filepath.WalkDir(root, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if path == root || d.IsDir() {
			return nil
		}
		info, err := d.Info()
		if err != nil {
			return err
		}
		if now.Sub(info.ModTime()) > maxAge {
			return os.Remove(path)
		}
		return nil
	})
}

func movePath(src, dst string) error {
	if err := os.Rename(src, dst); err == nil {
		return nil
	} else if !errors.Is(err, syscall.EXDEV) {
		return err
	}
	if _, err := os.Lstat(dst); err == nil {
		return fmt.Errorf("destination already exists: %s", dst)
	} else if !os.IsNotExist(err) {
		return err
	}
	if err := copyPath(src, dst); err != nil {
		return err
	}
	return os.RemoveAll(src)
}

func copyPath(src, dst string) error {
	info, err := os.Lstat(src)
	if err != nil {
		return err
	}
	if info.Mode()&os.ModeSymlink != 0 {
		target, err := os.Readlink(src)
		if err != nil {
			return err
		}
		return os.Symlink(target, dst)
	}
	if info.IsDir() {
		if err := os.MkdirAll(dst, info.Mode().Perm()); err != nil {
			return err
		}
		entries, err := os.ReadDir(src)
		if err != nil {
			return err
		}
		for _, entry := range entries {
			if err := copyPath(filepath.Join(src, entry.Name()), filepath.Join(dst, entry.Name())); err != nil {
				return err
			}
		}
		return os.Chtimes(dst, info.ModTime(), info.ModTime())
	}
	in, err := os.Open(src)
	if err != nil {
		return err
	}
	defer in.Close()
	out, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_EXCL, info.Mode().Perm())
	if err != nil {
		return err
	}
	_, copyErr := io.Copy(out, in)
	closeErr := out.Close()
	if copyErr != nil {
		_ = os.Remove(dst)
		return copyErr
	}
	if closeErr != nil {
		_ = os.Remove(dst)
		return closeErr
	}
	return os.Chtimes(dst, info.ModTime(), info.ModTime())
}

func (s Local) Rename(a, b string) error {
	pa, e := s.real(a)
	if e != nil {
		return e
	}
	pb, e := s.real(b)
	if e != nil {
		return e
	}
	return movePath(pa, pb)
}
func (s Local) MkdirAll(path string) error {
	p, e := s.real(path)
	if e != nil {
		return e
	}
	return os.MkdirAll(p, 0755)
}
func (s Local) List(path string) ([]os.FileInfo, error) {
	p, e := s.real(path)
	if e != nil {
		return nil, e
	}
	f, e := os.Open(p)
	if e != nil {
		return nil, e
	}
	defer f.Close()
	items, err := f.Readdir(-1)
	if err != nil {
		return nil, err
	}
	sort.Slice(items, func(i, j int) bool { return items[i].Name() < items[j].Name() })
	return items, nil
}

var _ fs.FS