package inotify

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"syscall"
	"unsafe"

	"golang.org/x/sys/unix"
)

var ErrEventOverflow = fmt.Errorf("inotify event queue overflowed")

type Event struct {
	Name  string
	Path  string
	IsDir bool
}

type Watcher struct {
	Events   chan Event
	Errors   chan error
	fd       int
	poller   *poller
	pW       map[int32]watch
	wP       map[string]int
	wPLock   *sync.Mutex
	pWLock   *sync.Mutex
	done     chan bool
	isClosed bool
}

func (w *Watcher) Path() []string {
	paths := make([]string, 0)

	if w.isClosed {
		return paths
	}

	w.wPLock.Lock()
	defer w.wPLock.Unlock()

	for path := range w.wP {
		paths = append(paths, path)
	}

	return paths
}

func NewWatcher() (*Watcher, error) {
	fd, err := unix.InotifyInit1(unix.IN_NONBLOCK)
	if err != nil {
		return nil, err
	}
	poller, err := newPoller(fd)
	if err != nil {
		return nil, err
	}
	w := &Watcher{
		fd:     fd,
		poller: poller,
		Events: make(chan Event),
		Errors: make(chan error),
		pW:     make(map[int32]watch),
		pWLock: new(sync.Mutex),
		wP:     make(map[string]int),
		wPLock: new(sync.Mutex),
		done:   make(chan bool),
	}
	go w.eventLoop()
	return w, nil
}

const bufsize = unix.SizeofInotifyEvent + syscall.NAME_MAX + 1

type eventBuf [bufsize]byte

func (w *Watcher) readEvent(buf eventBuf, n int) {
	var offset uint32
	for offset <= uint32(n-unix.SizeofInotifyEvent) {
		event := (*unix.InotifyEvent)(unsafe.Pointer(&buf[offset]))
		if event.Mask&unix.IN_Q_OVERFLOW == unix.IN_Q_OVERFLOW {
			w.Errors <- ErrEventOverflow
			break
		}

		var name string
		w.pWLock.Lock()
		path := w.pW[event.Wd]
		w.pWLock.Unlock()

		if event.Len > 0 {
			rawName := (*[unix.PathMax]byte)(unsafe.Pointer(&buf[offset+unix.SizeofInotifyEvent]))[:event.Len:event.Len]
			name = strings.TrimRight(string(rawName[0:event.Len]), "\000")
		}

		var isDir bool
		if isDeleteSelf(event.Mask) {
			isDir = path.isDir
			w.remove(event.Wd)
		} else {
			isDir = isDirectory(event.Mask)
		}

		if !isIgnore(event.Mask) {
			w.Events <- Event{
				Name:  maskString(event.Mask),
				Path:  filepath.Join(path.name, name),
				IsDir: isDir,
			}
		}

		offset += event.Len + unix.SizeofInotifyEvent
	}
}

func (w *Watcher) Close() {
	if w.isClosed {
		return
	}
	w.poller.close()
	w.done <- true
	close(w.Errors)
	close(w.Events)
	close(w.done)
}

func (w *Watcher) readEventLoop() {
	var (
		n   int
		err error
		buf eventBuf
	)

	for {
		select {
		case <-w.done:
			return
		default:
		}

		n, err = unix.Read(w.fd, buf[:])
		if err != nil {
			if err == unix.EINTR {
				break
			}
			if err == unix.EAGAIN {
				break
			}
			w.Errors <- err
			continue
		}

		if n < unix.SizeofInotifyEvent {
			w.Errors <- fmt.Errorf("event is too short")
			break
		}

		w.readEvent(buf, n)
	}

}

func (w *Watcher) eventLoop() {
	var (
		ok  bool
		err error
	)

	for {
		ok, err = w.poller.wait()
		if err != nil {
			w.Errors <- err
			continue
		}
		if !ok {
			continue
		}
		w.readEventLoop()
	}
}

func (w *Watcher) remove(wd int32) {
	w.pWLock.Lock()
	defer w.pWLock.Unlock()
	name, ok := w.pW[wd]
	if !ok {
		return
	}
	delete(w.pW, wd)

	w.wPLock.Lock()
	defer w.wPLock.Unlock()
	delete(w.wP, name.name)
}

type watch struct {
	name  string
	isDir bool
}

func (w *Watcher) AddWatch(name string) error {
	name = filepath.Clean(name)
	wd, err := unix.InotifyAddWatch(w.fd, name, unix.IN_ALL_EVENTS)
	if err != nil {
		return err
	}

	w.pWLock.Lock()
	w.pW[int32(wd)] = watch{name: name, isDir: !isExistFile(name)}
	w.pWLock.Unlock()

	w.wPLock.Lock()
	w.wP[name] = wd
	w.wPLock.Unlock()

	return nil
}

func (w *Watcher) RemoveWatch(name string) error {
	name = filepath.Clean(name)
	w.wPLock.Lock()
	defer w.wPLock.Unlock()
	wd, ok := w.wP[name]
	if !ok {
		return fmt.Errorf("can't remove non-existent inotify watch for: %s", name)
	}
	delete(w.wP, name)

	w.pWLock.Lock()
	defer w.pWLock.Unlock()
	delete(w.pW, int32(wd))

	_, err := unix.InotifyRmWatch(w.fd, uint32(wd))
	return err
}

func maskString(mask uint32) string {
	for key, value := range eventName {
		if key&mask != 0 {
			return value
		}
	}
	return EventUnknown
}

const (
	EventAccess       = "IN_ACCESS"
	EventAttrib       = "IN_ATTRIB"
	EventCloseWrite   = "IN_CLOSE_WRITE"
	EventCloseNoWrite = "IN_CLOSE_NOWRITE"
	EventCreate       = "IN_CREATE"
	EventDelete       = "IN_DELETE"
	EventDeleteSelf   = "IN_DELETE_SELF"
	EventModify       = "IN_MODIFY"
	EventMoveSelf     = "IN_MOVE_SELF"
	EventMovedFrom    = "IN_MOVED_FROM"
	EventMovedTo      = "IN_MOVED_TO"
	EventOpen         = "IN_OPEN"
	EventIgnored      = "IN_IGNORED"
	EventUnmount      = "IN_UNMOUNT"
	EventUnknown      = "UNKNOWN"
)

var eventName = map[uint32]string{
	unix.IN_ACCESS:        EventAccess,
	unix.IN_ATTRIB:        EventAttrib,
	unix.IN_CLOSE_WRITE:   EventCloseWrite,
	unix.IN_CLOSE_NOWRITE: EventCloseNoWrite,
	unix.IN_CREATE:        EventCreate,
	unix.IN_DELETE:        EventDelete,
	unix.IN_DELETE_SELF:   EventDeleteSelf,
	unix.IN_MODIFY:        EventModify,
	unix.IN_MOVE_SELF:     EventMoveSelf,
	unix.IN_MOVED_FROM:    EventMovedFrom,
	unix.IN_MOVED_TO:      EventMovedTo,
	unix.IN_OPEN:          EventOpen,
	unix.IN_IGNORED:       EventIgnored,
	unix.IN_UNMOUNT:       EventUnmount,
}

func isDirectory(mask uint32) bool {
	return mask&unix.IN_ISDIR == unix.IN_ISDIR
}

func isIgnore(mask uint32) bool {
	return mask&unix.IN_IGNORED == unix.IN_IGNORED
}

func isDeleteSelf(mask uint32) bool {
	return mask&unix.IN_DELETE_SELF == unix.IN_DELETE_SELF
}

func isExistFile(name string) bool {
	f, err := os.Stat(name)
	return err == nil && !f.IsDir()
}