// Package vfs is the filesystem abstraction both sides of haul are driven
// through: the local disk and a remote SFTP connection look identical to the
// transfer engine (internal/xfer) and to the browser panes (internal/ui).
//
// The two differ in more than their I/O calls — local paths use the native
// separator and a platform-specific root, remote paths are always "/"-separated
// — so path manipulation is part of the interface rather than something callers
// are trusted to get right per side.
package vfs

import (
	"io"
	"os"
	"path"
	"path/filepath"
	"strings"

	"github.com/pkg/sftp"
)

// FS is the filesystem surface haul needs. Read/write methods cover the copy
// engine; the path helpers and the mutating operations cover the browser.
type FS interface {
	// Open opens a file for reading with seek support (needed to resume).
	Open(p string) (io.ReadSeekCloser, error)
	// Create truncates/creates a file for writing.
	Create(p string) (io.WriteCloser, error)
	// OpenAt opens an existing file for writing positioned at offset, used to
	// resume a partial transfer. (SFTP O_APPEND is unreliable — pkg/sftp writes
	// at an explicit offset — so we seek instead.)
	OpenAt(p string, offset int64) (io.WriteCloser, error)
	Stat(p string) (os.FileInfo, error)
	ReadDir(p string) ([]os.FileInfo, error)
	MkdirAll(p string) error
	Join(elem ...string) string
	Base(p string) string

	// Dir returns p's parent directory.
	Dir(p string) string
	// IsRoot reports whether p has no parent to ascend to.
	IsRoot(p string) bool
	// Home is the directory a pane opens at: the user's home, falling back to
	// the working directory and then the root.
	Home() string
	// Mkdir creates a single directory.
	Mkdir(p string) error
	// Remove deletes a file, or a directory and everything under it.
	Remove(p string) error
	// Rename moves oldPath to newPath within this filesystem.
	Rename(oldPath, newPath string) error
}

// Local is the local disk, using os + filepath (native separators).
type Local struct{}

func (Local) Open(p string) (io.ReadSeekCloser, error) { return os.Open(p) }
func (Local) Create(p string) (io.WriteCloser, error) {
	return os.OpenFile(p, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o644)
}
func (Local) OpenAt(p string, offset int64) (io.WriteCloser, error) {
	f, err := os.OpenFile(p, os.O_WRONLY, 0o644)
	if err != nil {
		return nil, err
	}
	if _, err := f.Seek(offset, io.SeekStart); err != nil {
		f.Close()
		return nil, err
	}
	return f, nil
}
func (Local) Stat(p string) (os.FileInfo, error)      { return os.Stat(p) }
func (Local) MkdirAll(p string) error                 { return os.MkdirAll(p, 0o755) }
func (Local) Join(elem ...string) string              { return filepath.Join(elem...) }
func (Local) Base(p string) string                    { return filepath.Base(p) }
func (Local) ReadDir(p string) ([]os.FileInfo, error) { return readDirInfos(p) }
func (Local) Dir(p string) string                     { return filepath.Dir(p) }

// IsRoot is true when p is its own parent, which is how both "/" and "C:\"
// behave under filepath.Dir.
func (Local) IsRoot(p string) bool { return p == filepath.Dir(p) }

func (l Local) Home() string {
	if home, err := os.UserHomeDir(); err == nil {
		return home
	}
	if wd, err := os.Getwd(); err == nil {
		return wd
	}
	return string(filepath.Separator)
}

func (Local) Mkdir(p string) error     { return os.Mkdir(p, 0o755) }
func (Local) Remove(p string) error    { return os.RemoveAll(p) }
func (Local) Rename(a, b string) error { return os.Rename(a, b) }

func readDirInfos(p string) ([]os.FileInfo, error) {
	entries, err := os.ReadDir(p)
	if err != nil {
		return nil, err
	}
	out := make([]os.FileInfo, 0, len(entries))
	for _, e := range entries {
		fi, err := e.Info()
		if err != nil {
			// A file that vanished between the listing and the stat isn't an
			// error worth failing the whole directory over.
			continue
		}
		out = append(out, fi)
	}
	return out, nil
}

// Remote is the SFTP side, using the "/"-separated path package.
type Remote struct{ C *sftp.Client }

func (r Remote) Open(p string) (io.ReadSeekCloser, error) { return r.C.Open(p) }
func (r Remote) Create(p string) (io.WriteCloser, error) {
	return r.C.OpenFile(p, os.O_CREATE|os.O_WRONLY|os.O_TRUNC)
}
func (r Remote) OpenAt(p string, offset int64) (io.WriteCloser, error) {
	f, err := r.C.OpenFile(p, os.O_WRONLY)
	if err != nil {
		return nil, err
	}
	if _, err := f.Seek(offset, io.SeekStart); err != nil {
		f.Close()
		return nil, err
	}
	return f, nil
}
func (r Remote) Stat(p string) (os.FileInfo, error)      { return r.C.Stat(p) }
func (r Remote) MkdirAll(p string) error                 { return r.C.MkdirAll(p) }
func (r Remote) Join(elem ...string) string              { return path.Join(elem...) }
func (r Remote) Base(p string) string                    { return path.Base(p) }
func (r Remote) ReadDir(p string) ([]os.FileInfo, error) { return r.C.ReadDir(p) }
func (r Remote) Dir(p string) string                     { return path.Dir(p) }
func (r Remote) IsRoot(p string) bool                    { return p == "/" || p == "" }

// Home asks the server where it put us; the SFTP subsystem starts in the
// account's home directory, so Getwd is the answer without shelling out.
func (r Remote) Home() string {
	if wd, err := r.C.Getwd(); err == nil && wd != "" {
		return wd
	}
	return "/"
}

func (r Remote) Mkdir(p string) error     { return r.C.Mkdir(p) }
func (r Remote) Rename(a, b string) error { return r.C.Rename(a, b) }

// Remove deletes p, recursing into directories: SFTP's RemoveDirectory only
// works on empty directories, so the tree has to be walked bottom-up.
func (r Remote) Remove(p string) error {
	fi, err := r.C.Stat(p)
	if err != nil {
		return err
	}
	if !fi.IsDir() {
		return r.C.Remove(p)
	}
	entries, err := r.C.ReadDir(p)
	if err != nil {
		return err
	}
	for _, e := range entries {
		if err := r.Remove(path.Join(p, e.Name())); err != nil {
			return err
		}
	}
	return r.C.RemoveDirectory(p)
}

// CleanPath normalises user-typed input for fs: trimming stray whitespace and
// collapsing "." and ".." segments, leaving a path fs can Stat.
func CleanPath(fs FS, p string) string {
	p = strings.TrimSpace(p)
	if p == "" {
		return fs.Home()
	}
	if _, ok := fs.(Remote); ok {
		return path.Clean(p)
	}
	return filepath.Clean(p)
}