1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Traits and associated utilities for dealing with abstract constraint filters.

pub use super::members::Contains;
use core::marker::PhantomData;

/// Trait to add a constraint onto the filter.
pub trait FilterStack<T>: Contains<T> {
	/// The type used to archive the stack.
	type Stack;

	/// Add a new `constraint` onto the filter.
	fn push(constraint: impl Fn(&T) -> bool + 'static);

	/// Removes the most recently pushed, and not-yet-popped, constraint from the filter.
	fn pop();

	/// Clear the filter, returning a value that may be used later to `restore` it.
	fn take() -> Self::Stack;

	/// Restore the filter from a previous `take` operation.
	fn restore(taken: Self::Stack);
}

/// Guard type for pushing a constraint to a `FilterStack` and popping when dropped.
pub struct FilterStackGuard<F: FilterStack<T>, T>(PhantomData<(F, T)>);

/// Guard type for clearing all pushed constraints from a `FilterStack` and reinstating them when
/// dropped.
pub struct ClearFilterGuard<F: FilterStack<T>, T>(Option<F::Stack>, PhantomData<T>);

impl<F: FilterStack<T>, T> FilterStackGuard<F, T> {
	/// Create a new instance, adding a new `constraint` onto the filter `T`, and popping it when
	/// this instance is dropped.
	pub fn new(constraint: impl Fn(&T) -> bool + 'static) -> Self {
		F::push(constraint);
		Self(PhantomData)
	}
}

impl<F: FilterStack<T>, T> Drop for FilterStackGuard<F, T> {
	fn drop(&mut self) {
		F::pop();
	}
}

impl<F: FilterStack<T>, T> ClearFilterGuard<F, T> {
	/// Create a new instance, adding a new `constraint` onto the filter `T`, and popping it when
	/// this instance is dropped.
	pub fn new() -> Self {
		Self(Some(F::take()), PhantomData)
	}
}

impl<F: FilterStack<T>, T> Drop for ClearFilterGuard<F, T> {
	fn drop(&mut self) {
		if let Some(taken) = self.0.take() {
			F::restore(taken);
		}
	}
}

/// Simple trait for providing a filter over a reference to some type, given an instance of itself.
pub trait InstanceFilter<T>: Sized + Send + Sync {
	/// Determine if a given value should be allowed through the filter (returns `true`) or not.
	fn filter(&self, _: &T) -> bool;

	/// Determines whether `self` matches at least everything that `_o` does.
	fn is_superset(&self, _o: &Self) -> bool {
		false
	}
}

impl<T> InstanceFilter<T> for () {
	fn filter(&self, _: &T) -> bool {
		true
	}
	fn is_superset(&self, _o: &Self) -> bool {
		true
	}
}

#[macro_export]
macro_rules! impl_filter_stack {
	($target:ty, $base:ty, $call:ty, $module:ident) => {
		#[cfg(feature = "std")]
		mod $module {
			#[allow(unused_imports)]
			use super::*;
			use std::{boxed::Box, cell::RefCell, mem::{swap, take}, vec::Vec};
			use $crate::traits::filter::{Contains, FilterStack};

			thread_local! {
				static FILTER: RefCell<Vec<Box<dyn Fn(&$call) -> bool + 'static>>> = RefCell::new(Vec::new());
			}

			impl Contains<$call> for $target {
				fn contains(call: &$call) -> bool {
					<$base>::contains(call) &&
						FILTER.with(|filter| filter.borrow().iter().all(|f| f(call)))
				}
			}

			impl FilterStack<$call> for $target {
				type Stack = Vec<Box<dyn Fn(&$call) -> bool + 'static>>;
				fn push(f: impl Fn(&$call) -> bool + 'static) {
					FILTER.with(|filter| filter.borrow_mut().push(Box::new(f)));
				}
				fn pop() {
					FILTER.with(|filter| filter.borrow_mut().pop());
				}
				fn take() -> Self::Stack {
					FILTER.with(|filter| take(filter.borrow_mut().as_mut()))
				}
				fn restore(mut s: Self::Stack) {
					FILTER.with(|filter| swap(filter.borrow_mut().as_mut(), &mut s));
				}
			}
		}

		#[cfg(not(feature = "std"))]
		mod $module {
			#[allow(unused_imports)]
			use super::*;
			use $crate::traits::{swap, take, RefCell, Vec, Box, Contains, FilterStack};

			struct ThisFilter(RefCell<Vec<Box<dyn Fn(&$call) -> bool + 'static>>>);
			// NOTE: Safe only in wasm (guarded above) because there's only one thread.
			unsafe impl Send for ThisFilter {}
			unsafe impl Sync for ThisFilter {}

			static FILTER: ThisFilter = ThisFilter(RefCell::new(Vec::new()));

			impl Contains<$call> for $target {
				fn contains(call: &$call) -> bool {
					<$base>::contains(call) && FILTER.0.borrow().iter().all(|f| f(call))
				}
			}

			impl FilterStack<$call> for $target {
				type Stack = Vec<Box<dyn Fn(&$call) -> bool + 'static>>;
				fn push(f: impl Fn(&$call) -> bool + 'static) {
					FILTER.0.borrow_mut().push(Box::new(f));
				}
				fn pop() {
					FILTER.0.borrow_mut().pop();
				}
				fn take() -> Self::Stack {
					take(FILTER.0.borrow_mut().as_mut())
				}
				fn restore(mut s: Self::Stack) {
					swap(FILTER.0.borrow_mut().as_mut(), &mut s);
				}
			}
		}
	}
}

#[cfg(test)]
pub mod test_impl_filter_stack {
	use super::*;

	pub struct IsCallable;
	pub struct BaseFilter;
	impl Contains<u32> for BaseFilter {
		fn contains(x: &u32) -> bool {
			x % 2 == 0
		}
	}
	impl_filter_stack!(
		crate::traits::filter::test_impl_filter_stack::IsCallable,
		crate::traits::filter::test_impl_filter_stack::BaseFilter,
		u32,
		is_callable
	);

	#[test]
	fn impl_filter_stack_should_work() {
		assert!(IsCallable::contains(&36));
		assert!(IsCallable::contains(&40));
		assert!(IsCallable::contains(&42));
		assert!(!IsCallable::contains(&43));

		IsCallable::push(|x| *x < 42);
		assert!(IsCallable::contains(&36));
		assert!(IsCallable::contains(&40));
		assert!(!IsCallable::contains(&42));

		IsCallable::push(|x| *x % 3 == 0);
		assert!(IsCallable::contains(&36));
		assert!(!IsCallable::contains(&40));

		IsCallable::pop();
		assert!(IsCallable::contains(&36));
		assert!(IsCallable::contains(&40));
		assert!(!IsCallable::contains(&42));

		let saved = IsCallable::take();
		assert!(IsCallable::contains(&36));
		assert!(IsCallable::contains(&40));
		assert!(IsCallable::contains(&42));
		assert!(!IsCallable::contains(&43));

		IsCallable::restore(saved);
		assert!(IsCallable::contains(&36));
		assert!(IsCallable::contains(&40));
		assert!(!IsCallable::contains(&42));

		IsCallable::pop();
		assert!(IsCallable::contains(&36));
		assert!(IsCallable::contains(&40));
		assert!(IsCallable::contains(&42));
		assert!(!IsCallable::contains(&43));
	}

	#[test]
	fn guards_should_work() {
		assert!(IsCallable::contains(&36));
		assert!(IsCallable::contains(&40));
		assert!(IsCallable::contains(&42));
		assert!(!IsCallable::contains(&43));
		{
			let _guard_1 = FilterStackGuard::<IsCallable, u32>::new(|x| *x < 42);
			assert!(IsCallable::contains(&36));
			assert!(IsCallable::contains(&40));
			assert!(!IsCallable::contains(&42));
			{
				let _guard_2 = FilterStackGuard::<IsCallable, u32>::new(|x| *x % 3 == 0);
				assert!(IsCallable::contains(&36));
				assert!(!IsCallable::contains(&40));
			}
			assert!(IsCallable::contains(&36));
			assert!(IsCallable::contains(&40));
			assert!(!IsCallable::contains(&42));
			{
				let _guard_2 = ClearFilterGuard::<IsCallable, u32>::new();
				assert!(IsCallable::contains(&36));
				assert!(IsCallable::contains(&40));
				assert!(IsCallable::contains(&42));
				assert!(!IsCallable::contains(&43));
			}
			assert!(IsCallable::contains(&36));
			assert!(IsCallable::contains(&40));
			assert!(!IsCallable::contains(&42));
		}
		assert!(IsCallable::contains(&36));
		assert!(IsCallable::contains(&40));
		assert!(IsCallable::contains(&42));
		assert!(!IsCallable::contains(&43));
	}
}