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

//-
// Copyright 2017 Jason Lingle
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use crate::std_facade::{fmt, Arc};

use crate::strategy::traits::*;
use crate::test_runner::*;

/// `Strategy` and `ValueTree` filter adaptor.
///
/// See `Strategy::prop_filter()`.
#[must_use = "strategies do nothing unless used"]
pub struct Filter<S, F> {
    pub(super) source: S,
    pub(super) whence: Reason,
    pub(super) fun: Arc<F>,
}

impl<S, F> Filter<S, F> {
    pub(super) fn new(source: S, whence: Reason, fun: F) -> Self {
        Self {
            source,
            whence,
            fun: Arc::new(fun),
        }
    }
}

impl<S: fmt::Debug, F> fmt::Debug for Filter<S, F> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Filter")
            .field("source", &self.source)
            .field("whence", &self.whence)
            .field("fun", &"<function>")
            .finish()
    }
}

impl<S: Clone, F> Clone for Filter<S, F> {
    fn clone(&self) -> Self {
        Filter {
            source: self.source.clone(),
            whence: "unused".into(),
            fun: Arc::clone(&self.fun),
        }
    }
}

impl<S: Strategy, F: Fn(&S::Value) -> bool> Strategy for Filter<S, F> {
    type Tree = Filter<S::Tree, F>;
    type Value = S::Value;

    fn new_tree(&self, runner: &mut TestRunner) -> NewTree<Self> {
        loop {
            let val = self.source.new_tree(runner)?;
            if !(self.fun)(&val.current()) {
                runner.reject_local(self.whence.clone())?;
            } else {
                return Ok(Filter {
                    source: val,
                    whence: self.whence.clone(),
                    fun: Arc::clone(&self.fun),
                });
            }
        }
    }
}

impl<S: ValueTree, F: Fn(&S::Value) -> bool> Filter<S, F> {
    fn ensure_acceptable(&mut self) {
        while !(self.fun)(&self.source.current()) {
            if !self.source.complicate() {
                panic!(
                    "Unable to complicate filtered strategy \
                     back into acceptable value"
                );
            }
        }
    }
}

impl<S: ValueTree, F: Fn(&S::Value) -> bool> ValueTree for Filter<S, F> {
    type Value = S::Value;

    fn current(&self) -> S::Value {
        self.source.current()
    }

    fn simplify(&mut self) -> bool {
        if self.source.simplify() {
            self.ensure_acceptable();
            true
        } else {
            false
        }
    }

    fn complicate(&mut self) -> bool {
        if self.source.complicate() {
            self.ensure_acceptable();
            true
        } else {
            false
        }
    }
}

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

    #[test]
    fn test_filter() {
        let input = (0..256).prop_filter("%3", |&v| 0 == v % 3);

        for _ in 0..256 {
            let mut runner = TestRunner::default();
            let mut case = input.new_tree(&mut runner).unwrap();

            assert!(0 == case.current() % 3);

            while case.simplify() {
                assert!(0 == case.current() % 3);
            }
            assert!(0 == case.current() % 3);
        }
    }

    #[test]
    fn test_filter_sanity() {
        check_strategy_sanity(
            (0..256).prop_filter("!%5", |&v| 0 != v % 5),
            Some(CheckStrategySanityOptions {
                // Due to internal rejection sampling, `simplify()` can
                // converge back to what `complicate()` would do.
                strict_complicate_after_simplify: false,
                ..CheckStrategySanityOptions::default()
            }),
        );
    }
}