// Copyright (c) 2014-2015 The Notify Authors. All rights reserved.
// Use of this source code is governed by the MIT license that can be
// found in the LICENSE file.

package notify

import "errors"

var (
	errAlreadyWatched  = errors.New("path is already watched")
	errNotWatched      = errors.New("path is not being watched")
	errInvalidEventSet = errors.New("invalid event set provided")
)

// Watcher is a intermediate interface for wrapping inotify, ReadDirChangesW,
// FSEvents, kqueue and poller implementations.
//
// The watcher implementation is expected to do its own mapping between paths and
// create watchers if underlying event notification does not support it. For
// the ease of implementation it is guaranteed that paths provided via Watch and
// Unwatch methods are absolute and clean.
type watcher interface {
	// Watch requests a watcher creation for the given path and given event set.
	Watch(path string, event Event) error

	// Unwatch requests a watcher deletion for the given path and given event set.
	Unwatch(path string) error

	// Rewatch provides a functionality for modifying existing watch-points, like
	// expanding its event set.
	//
	// Rewatch modifies existing watch-point under for the given path. It passes
	// the existing event set currently registered for the given path, and the
	// new, requested event set.
	//
	// It is guaranteed that Tree will not pass to Rewatch zero value for any
	// of its arguments. If old == new and watcher can be upgraded to
	// recursiveWatcher interface, a watch for the corresponding path is expected
	// to be changed from recursive to the non-recursive one.
	Rewatch(path string, old, new Event) error

	// Close unwatches all paths that are registered. When Close returns, it
	// is expected it will report no more events.
	Close() error
}

// RecursiveWatcher is an interface for a Watcher for those OS, which do support
// recursive watching over directories.
type recursiveWatcher interface {
	RecursiveWatch(path string, event Event) error

	// RecursiveUnwatch removes a recursive watch-point given by the path. For
	// native recursive implementation there is no difference in functionality
	// between Unwatch and RecursiveUnwatch, however for those platforms, that
	// requires emulation for recursive watch-points, the implementation differs.
	RecursiveUnwatch(path string) error

	// RecursiveRewatcher provides a functionality for modifying and/or relocating
	// existing recursive watch-points.
	//
	// To relocate a watch-point means to unwatch oldpath and set a watch-point on
	// newpath.
	//
	// To modify a watch-point means either to expand or shrink its event set.
	//
	// Tree can want to either relocate, modify or relocate and modify a watch-point
	// via single RecursiveRewatch call.
	//
	// If oldpath == newpath, the watch-point is expected to change its event set value
	// from oldevent to newevent.
	//
	// If oldevent == newevent, the watch-point is expected to relocate from oldpath
	// to the newpath.
	//
	// If oldpath != newpath and oldevent != newevent, the watch-point is expected
	// to relocate from oldpath to the newpath first and then change its event set
	// value from oldevent to the newevent. In other words the end result must be
	// a watch-point set on newpath with newevent value of its event set.
	//
	// It is guaranteed that Tree will not pass to RecurisveRewatcha zero value
	// for any of its arguments. If oldpath == newpath and oldevent == newevent,
	// a watch for the corresponding path is expected to be changed for
	// non-recursive to the recursive one.
	RecursiveRewatch(oldpath, newpath string, oldevent, newevent Event) error
}