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// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
enum GestureDisposition {
accepted,
rejected
}
/// Represents an object participating in an arena.
///
/// Receives callbacks from the GestureArena to notify the object when it wins
/// or loses a gesture negotiation. Exactly one of [acceptGesture] or
/// [rejectGesture] will be called for each arena key this member was added to,
/// regardless of what caused the arena to be resolved. For example, if a
/// member resolves the arena itself, that member still receives an
/// [acceptGesture] callback.
abstract class GestureArenaMember {
/// Called when this member wins the arena for the given key.
void acceptGesture(Object key);
/// Called when this member loses the arena for the given key.
void rejectGesture(Object key);
}
/// An interface to information to an arena
///
/// A given [GestureArenaMember] can have multiple entries in multiple arenas
/// with different keys.
class GestureArenaEntry {
GestureArenaEntry._(this._arena, this._key, this._member);
final GestureArena _arena;
final Object _key;
final GestureArenaMember _member;
/// Call this member to claim victory (with accepted) or admit defeat (with rejected).
///
/// It's fine to attempt to resolve an arena that is already resolved.
void resolve(GestureDisposition disposition) {
_arena._resolve(_key, _member, disposition);
}
}
class _GestureArenaState {
final List<GestureArenaMember> members = new List<GestureArenaMember>();
bool isOpen = true;
void add(GestureArenaMember member) {
assert(isOpen);
members.add(member);
}
}
/// The first member to accept or the last member to not to reject wins.
class GestureArena {
final Map<Object, _GestureArenaState> _arenas = new Map<Object, _GestureArenaState>();
static final GestureArena instance = new GestureArena();
GestureArenaEntry add(Object key, GestureArenaMember member) {
_GestureArenaState state = _arenas.putIfAbsent(key, () => new _GestureArenaState());
state.add(member);
return new GestureArenaEntry._(this, key, member);
}
void close(Object key) {
_GestureArenaState state = _arenas[key];
if (state == null)
return; // This arena either never existed or has been resolved.
state.isOpen = false;
_tryToResolveArena(key, state);
}
void _tryToResolveArena(Object key, _GestureArenaState state) {
assert(_arenas[key] == state);
assert(!state.isOpen);
if (state.members.length == 1) {
_arenas.remove(key);
state.members.first.acceptGesture(key);
} else if (state.members.isEmpty) {
_arenas.remove(key);
}
}
void _resolve(Object key, GestureArenaMember member, GestureDisposition disposition) {
_GestureArenaState state = _arenas[key];
if (state == null)
return; // This arena has already resolved.
assert(!state.isOpen);
assert(state.members.contains(member));
if (disposition == GestureDisposition.rejected) {
state.members.remove(member);
member.rejectGesture(key);
_tryToResolveArena(key, state);
} else {
assert(disposition == GestureDisposition.accepted);
_arenas.remove(key);
for (GestureArenaMember rejectedMember in state.members) {
if (rejectedMember != member)
rejectedMember.rejectGesture(key);
}
member.acceptGesture(key);
}
}
}