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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// +build windows

// Package winfsnotify allows the user to receive
// file system event notifications on Windows.
package winfsnotify

import (
        "errors"
        "fmt"
        "os"
        "path/filepath"
        "runtime"
        "syscall"
        "unsafe"
)

// Event is the type of the notification messages
// received on the watcher's Event channel.
type Event struct {
        Mask   uint32 // Mask of events
        Cookie uint32 // Unique cookie associating related events (for rename)
        Name   string // File name (optional)
}

const (
        opAddWatch = iota
        opRemoveWatch
)

const (
        provisional uint64 = 1 << (32 + iota)
)

type input struct {
        op    int
        path  string
        flags uint32
        reply chan error
}

type inode struct {
        handle syscall.Handle
        volume uint32
        index  uint64
}

type watch struct {
        ov     syscall.Overlapped
        ino    *inode            // i-number
        path   string            // Directory path
        mask   uint64            // Directory itself is being watched with these notify flags
        names  map[string]uint64 // Map of names being watched and their notify flags
        rename string            // Remembers the old name while renaming a file
        buf    [4096]byte
}

type indexMap map[uint64]*watch
type watchMap map[uint32]indexMap

// A Watcher waits for and receives event notifications
// for a specific set of files and directories.
type Watcher struct {
        port     syscall.Handle // Handle to completion port
        watches  watchMap       // Map of watches (key: i-number)
        input    chan *input    // Inputs to the reader are sent on this channel
        Event    chan *Event    // Events are returned on this channel
        Error    chan error     // Errors are sent on this channel
        isClosed bool           // Set to true when Close() is first called
        quit     chan chan<- error
        cookie   uint32
}

// NewWatcher creates and returns a Watcher.
func NewWatcher() (*Watcher, error) {
        port, e := syscall.CreateIoCompletionPort(syscall.InvalidHandle, 0, 0, 0)
        if e != nil {
                return nil, os.NewSyscallError("CreateIoCompletionPort", e)
        }
        w := &Watcher{
                port:    port,
                watches: make(watchMap),
                input:   make(chan *input, 1),
                Event:   make(chan *Event, 50),
                Error:   make(chan error),
                quit:    make(chan chan<- error, 1),
        }
        go w.readEvents()
        return w, nil
}

// Close closes a Watcher.
// It sends a message to the reader goroutine to quit and removes all watches
// associated with the watcher.
func (w *Watcher) Close() error {
        if w.isClosed {
                return nil
        }
        w.isClosed = true

        // Send "quit" message to the reader goroutine
        ch := make(chan error)
        w.quit <- ch
        if err := w.wakeupReader(); err != nil {
                return err
        }
        return <-ch
}

// AddWatch adds path to the watched file set.
func (w *Watcher) AddWatch(path string, flags uint32) error {
        if w.isClosed {
                return errors.New("watcher already closed")
        }
        in := &input{
                op:    opAddWatch,
                path:  filepath.Clean(path),
                flags: flags,
                reply: make(chan error),
        }
        w.input <- in
        if err := w.wakeupReader(); err != nil {
                return err
        }
        return <-in.reply
}

// Watch adds path to the watched file set, watching all events.
func (w *Watcher) Watch(path string) error {
        return w.AddWatch(path, FS_ALL_EVENTS)
}

// RemoveWatch removes path from the watched file set.
func (w *Watcher) RemoveWatch(path string) error {
        in := &input{
                op:    opRemoveWatch,
                path:  filepath.Clean(path),
                reply: make(chan error),
        }
        w.input <- in
        if err := w.wakeupReader(); err != nil {
                return err
        }
        return <-in.reply
}

func (w *Watcher) wakeupReader() error {
        e := syscall.PostQueuedCompletionStatus(w.port, 0, 0, nil)
        if e != nil {
                return os.NewSyscallError("PostQueuedCompletionStatus", e)
        }
        return nil
}

func getDir(pathname string) (dir string, err error) {
        attr, e := syscall.GetFileAttributes(syscall.StringToUTF16Ptr(pathname))
        if e != nil {
                return "", os.NewSyscallError("GetFileAttributes", e)
        }
        if attr&syscall.FILE_ATTRIBUTE_DIRECTORY != 0 {
                dir = pathname
        } else {
                dir, _ = filepath.Split(pathname)
                dir = filepath.Clean(dir)
        }
        return
}

func getIno(path string) (ino *inode, err error) {
        h, e := syscall.CreateFile(syscall.StringToUTF16Ptr(path),
                syscall.FILE_LIST_DIRECTORY,
                syscall.FILE_SHARE_READ|syscall.FILE_SHARE_WRITE|syscall.FILE_SHARE_DELETE,
                nil, syscall.OPEN_EXISTING,
                syscall.FILE_FLAG_BACKUP_SEMANTICS|syscall.FILE_FLAG_OVERLAPPED, 0)
        if e != nil {
                return nil, os.NewSyscallError("CreateFile", e)
        }
        var fi syscall.ByHandleFileInformation
        if e = syscall.GetFileInformationByHandle(h, &fi); e != nil {
                syscall.CloseHandle(h)
                return nil, os.NewSyscallError("GetFileInformationByHandle", e)
        }
        ino = &inode{
                handle: h,
                volume: fi.VolumeSerialNumber,
                index:  uint64(fi.FileIndexHigh)<<32 | uint64(fi.FileIndexLow),
        }
        return ino, nil
}

// Must run within the I/O thread.
func (m watchMap) get(ino *inode) *watch {
        if i := m[ino.volume]; i != nil {
                return i[ino.index]
        }
        return nil
}

// Must run within the I/O thread.
func (m watchMap) set(ino *inode, watch *watch) {
        i := m[ino.volume]
        if i == nil {
                i = make(indexMap)
                m[ino.volume] = i
        }
        i[ino.index] = watch
}

// Must run within the I/O thread.
func (w *Watcher) addWatch(pathname string, flags uint64) error {
        dir, err := getDir(pathname)
        if err != nil {
                return err
        }
        if flags&FS_ONLYDIR != 0 && pathname != dir {
                return nil
        }
        ino, err := getIno(dir)
        if err != nil {
                return err
        }
        watchEntry := w.watches.get(ino)
        if watchEntry == nil {
                if _, e := syscall.CreateIoCompletionPort(ino.handle, w.port, 0, 0); e != nil {
                        syscall.CloseHandle(ino.handle)
                        return os.NewSyscallError("CreateIoCompletionPort", e)
                }
                watchEntry = &watch{
                        ino:   ino,
                        path:  dir,
                        names: make(map[string]uint64),
                }
                w.watches.set(ino, watchEntry)
                flags |= provisional
        } else {
                syscall.CloseHandle(ino.handle)
        }
        if pathname == dir {
                watchEntry.mask |= flags
        } else {
                watchEntry.names[filepath.Base(pathname)] |= flags
        }
        if err = w.startRead(watchEntry); err != nil {
                return err
        }
        if pathname == dir {
                watchEntry.mask &= ^provisional
        } else {
                watchEntry.names[filepath.Base(pathname)] &= ^provisional
        }
        return nil
}

// Must run within the I/O thread.
func (w *Watcher) removeWatch(pathname string) error {
        dir, err := getDir(pathname)
        if err != nil {
                return err
        }
        ino, err := getIno(dir)
        if err != nil {
                return err
        }
        watch := w.watches.get(ino)
        if watch == nil {
                return fmt.Errorf("can't remove non-existent watch for: %s", pathname)
        }
        if pathname == dir {
                w.sendEvent(watch.path, watch.mask&FS_IGNORED)
                watch.mask = 0
        } else {
                name := filepath.Base(pathname)
                w.sendEvent(watch.path+"/"+name, watch.names[name]&FS_IGNORED)
                delete(watch.names, name)
        }
        return w.startRead(watch)
}

// Must run within the I/O thread.
func (w *Watcher) deleteWatch(watch *watch) {
        for name, mask := range watch.names {
                if mask&provisional == 0 {
                        w.sendEvent(watch.path+"/"+name, mask&FS_IGNORED)
                }
                delete(watch.names, name)
        }
        if watch.mask != 0 {
                if watch.mask&provisional == 0 {
                        w.sendEvent(watch.path, watch.mask&FS_IGNORED)
                }
                watch.mask = 0
        }
}

// Must run within the I/O thread.
func (w *Watcher) startRead(watch *watch) error {
        if e := syscall.CancelIo(watch.ino.handle); e != nil {
                w.Error <- os.NewSyscallError("CancelIo", e)
                w.deleteWatch(watch)
        }
        mask := toWindowsFlags(watch.mask)
        for _, m := range watch.names {
                mask |= toWindowsFlags(m)
        }
        if mask == 0 {
                if e := syscall.CloseHandle(watch.ino.handle); e != nil {
                        w.Error <- os.NewSyscallError("CloseHandle", e)
                }
                delete(w.watches[watch.ino.volume], watch.ino.index)
                return nil
        }
        e := syscall.ReadDirectoryChanges(watch.ino.handle, &watch.buf[0],
                uint32(unsafe.Sizeof(watch.buf)), false, mask, nil, &watch.ov, 0)
        if e != nil {
                err := os.NewSyscallError("ReadDirectoryChanges", e)
                if e == syscall.ERROR_ACCESS_DENIED && watch.mask&provisional == 0 {
                        // Watched directory was probably removed
                        if w.sendEvent(watch.path, watch.mask&FS_DELETE_SELF) {
                                if watch.mask&FS_ONESHOT != 0 {
                                        watch.mask = 0
                                }
                        }
                        err = nil
                }
                w.deleteWatch(watch)
                w.startRead(watch)
                return err
        }
        return nil
}

// readEvents reads from the I/O completion port, converts the
// received events into Event objects and sends them via the Event channel.
// Entry point to the I/O thread.
func (w *Watcher) readEvents() {
        var (
                n, key uint32
                ov     *syscall.Overlapped
        )
        runtime.LockOSThread()

        for {
                e := syscall.GetQueuedCompletionStatus(w.port, &n, &key, &ov, syscall.INFINITE)
                watch := (*watch)(unsafe.Pointer(ov))

                if watch == nil {
                        select {
                        case ch := <-w.quit:
                                for _, index := range w.watches {
                                        for _, watch := range index {
                                                w.deleteWatch(watch)
                                                w.startRead(watch)
                                        }
                                }
                                var err error
                                if e := syscall.CloseHandle(w.port); e != nil {
                                        err = os.NewSyscallError("CloseHandle", e)
                                }
                                close(w.Event)
                                close(w.Error)
                                ch <- err
                                return
                        case in := <-w.input:
                                switch in.op {
                                case opAddWatch:
                                        in.reply <- w.addWatch(in.path, uint64(in.flags))
                                case opRemoveWatch:
                                        in.reply <- w.removeWatch(in.path)
                                }
                        default:
                        }
                        continue
                }

                switch e {
                case syscall.ERROR_ACCESS_DENIED:
                        // Watched directory was probably removed
                        w.sendEvent(watch.path, watch.mask&FS_DELETE_SELF)
                        w.deleteWatch(watch)
                        w.startRead(watch)
                        continue
                case syscall.ERROR_OPERATION_ABORTED:
                        // CancelIo was called on this handle
                        continue
                default:
                        w.Error <- os.NewSyscallError("GetQueuedCompletionPort", e)
                        continue
                case nil:
                }

                var offset uint32
                for {
                        if n == 0 {
                                w.Event <- &Event{Mask: FS_Q_OVERFLOW}
                                w.Error <- errors.New("short read in readEvents()")
                                break
                        }

                        // Point "raw" to the event in the buffer
                        raw := (*syscall.FileNotifyInformation)(unsafe.Pointer(&watch.buf[offset]))
                        buf := (*[syscall.MAX_PATH]uint16)(unsafe.Pointer(&raw.FileName))
                        name := syscall.UTF16ToString(buf[:raw.FileNameLength/2])
                        fullname := watch.path + "/" + name

                        var mask uint64
                        switch raw.Action {
                        case syscall.FILE_ACTION_REMOVED:
                                mask = FS_DELETE_SELF
                        case syscall.FILE_ACTION_MODIFIED:
                                mask = FS_MODIFY
                        case syscall.FILE_ACTION_RENAMED_OLD_NAME:
                                watch.rename = name
                        case syscall.FILE_ACTION_RENAMED_NEW_NAME:
                                if watch.names[watch.rename] != 0 {
                                        watch.names[name] |= watch.names[watch.rename]
                                        delete(watch.names, watch.rename)
                                        mask = FS_MOVE_SELF
                                }
                        }

                        sendNameEvent := func() {
                                if w.sendEvent(fullname, watch.names[name]&mask) {
                                        if watch.names[name]&FS_ONESHOT != 0 {
                                                delete(watch.names, name)
                                        }
                                }
                        }
                        if raw.Action != syscall.FILE_ACTION_RENAMED_NEW_NAME {
                                sendNameEvent()
                        }
                        if raw.Action == syscall.FILE_ACTION_REMOVED {
                                w.sendEvent(fullname, watch.names[name]&FS_IGNORED)
                                delete(watch.names, name)
                        }
                        if w.sendEvent(fullname, watch.mask&toFSnotifyFlags(raw.Action)) {
                                if watch.mask&FS_ONESHOT != 0 {
                                        watch.mask = 0
                                }
                        }
                        if raw.Action == syscall.FILE_ACTION_RENAMED_NEW_NAME {
                                fullname = watch.path + "/" + watch.rename
                                sendNameEvent()
                        }

                        // Move to the next event in the buffer
                        if raw.NextEntryOffset == 0 {
                                break
                        }
                        offset += raw.NextEntryOffset
                }

                if err := w.startRead(watch); err != nil {
                        w.Error <- err
                }
        }
}

func (w *Watcher) sendEvent(name string, mask uint64) bool {
        if mask == 0 {
                return false
        }
        event := &Event{Mask: uint32(mask), Name: name}
        if mask&FS_MOVE != 0 {
                if mask&FS_MOVED_FROM != 0 {
                        w.cookie++
                }
                event.Cookie = w.cookie
        }
        select {
        case ch := <-w.quit:
                w.quit <- ch
        case w.Event <- event:
        }
        return true
}

// String formats the event e in the form
// "filename: 0xEventMask = FS_ACCESS|FS_ATTRIB_|..."
func (e *Event) String() string {
        var events string
        m := e.Mask
        for _, b := range eventBits {
                if m&b.Value != 0 {
                        m &^= b.Value
                        events += "|" + b.Name
                }
        }
        if m != 0 {
                events += fmt.Sprintf("|%#x", m)
        }
        if len(events) > 0 {
                events = " == " + events[1:]
        }
        return fmt.Sprintf("%q: %#x%s", e.Name, e.Mask, events)
}

func toWindowsFlags(mask uint64) uint32 {
        var m uint32
        if mask&FS_ACCESS != 0 {
                m |= syscall.FILE_NOTIFY_CHANGE_LAST_ACCESS
        }
        if mask&FS_MODIFY != 0 {
                m |= syscall.FILE_NOTIFY_CHANGE_LAST_WRITE
        }
        if mask&FS_ATTRIB != 0 {
                m |= syscall.FILE_NOTIFY_CHANGE_ATTRIBUTES
        }
        if mask&(FS_MOVE|FS_CREATE|FS_DELETE) != 0 {
                m |= syscall.FILE_NOTIFY_CHANGE_FILE_NAME | syscall.FILE_NOTIFY_CHANGE_DIR_NAME
        }
        return m
}

func toFSnotifyFlags(action uint32) uint64 {
        switch action {
        case syscall.FILE_ACTION_ADDED:
                return FS_CREATE
        case syscall.FILE_ACTION_REMOVED:
                return FS_DELETE
        case syscall.FILE_ACTION_MODIFIED:
                return FS_MODIFY
        case syscall.FILE_ACTION_RENAMED_OLD_NAME:
                return FS_MOVED_FROM
        case syscall.FILE_ACTION_RENAMED_NEW_NAME:
                return FS_MOVED_TO
        }
        return 0
}

const (
        // Options for AddWatch
        FS_ONESHOT = 0x80000000
        FS_ONLYDIR = 0x1000000

        // Events
        FS_ACCESS      = 0x1
        FS_ALL_EVENTS  = 0xfff
        FS_ATTRIB      = 0x4
        FS_CLOSE       = 0x18
        FS_CREATE      = 0x100
        FS_DELETE      = 0x200
        FS_DELETE_SELF = 0x400
        FS_MODIFY      = 0x2
        FS_MOVE        = 0xc0
        FS_MOVED_FROM  = 0x40
        FS_MOVED_TO    = 0x80
        FS_MOVE_SELF   = 0x800

        // Special events
        FS_IGNORED    = 0x8000
        FS_Q_OVERFLOW = 0x4000
)

var eventBits = []struct {
        Value uint32
        Name  string
}{
        {FS_ACCESS, "FS_ACCESS"},
        {FS_ATTRIB, "FS_ATTRIB"},
        {FS_CREATE, "FS_CREATE"},
        {FS_DELETE, "FS_DELETE"},
        {FS_DELETE_SELF, "FS_DELETE_SELF"},
        {FS_MODIFY, "FS_MODIFY"},
        {FS_MOVED_FROM, "FS_MOVED_FROM"},
        {FS_MOVED_TO, "FS_MOVED_TO"},
        {FS_MOVE_SELF, "FS_MOVE_SELF"},
        {FS_IGNORED, "FS_IGNORED"},
        {FS_Q_OVERFLOW, "FS_Q_OVERFLOW"},
}