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
use crate::nodes::{BinaryOperator, Block, Expression};
use crate::process::{DefaultVisitor, Evaluator, NodeProcessor, NodeVisitor};
use crate::rules::{
    Context, FlawlessRule, RuleConfiguration, RuleConfigurationError, RuleProperties,
};

use super::verify_no_rule_properties;

#[derive(Debug, Clone, Default)]
struct Computer {
    evaluator: Evaluator,
}

impl Computer {
    fn replace_with(&mut self, expression: &Expression) -> Option<Expression> {
        match expression {
            Expression::Unary(_) => {
                if !self.evaluator.has_side_effects(expression) {
                    self.evaluator.evaluate(expression).to_expression()
                } else {
                    None
                }
            }
            Expression::Binary(binary) => {
                if !self.evaluator.has_side_effects(expression) {
                    self.evaluator
                        .evaluate(expression)
                        .to_expression()
                        .or_else(|| {
                            match binary.operator() {
                                BinaryOperator::And => {
                                    self.evaluator.evaluate(binary.left()).is_truthy().map(
                                        |is_truthy| {
                                            if is_truthy {
                                                binary.right().clone()
                                            } else {
                                                binary.left().clone()
                                            }
                                        },
                                    )
                                }
                                BinaryOperator::Or => {
                                    self.evaluator.evaluate(binary.left()).is_truthy().map(
                                        |is_truthy| {
                                            if is_truthy {
                                                binary.left().clone()
                                            } else {
                                                binary.right().clone()
                                            }
                                        },
                                    )
                                }
                                _ => None,
                            }
                            .map(|mut expression| {
                                self.process_expression(&mut expression);
                                expression
                            })
                        })
                } else {
                    match binary.operator() {
                        BinaryOperator::And => {
                            if !self.evaluator.has_side_effects(binary.left()) {
                                self.evaluator.evaluate(binary.left()).is_truthy().map(
                                    |is_truthy| {
                                        if is_truthy {
                                            binary.right().clone()
                                        } else {
                                            binary.left().clone()
                                        }
                                    },
                                )
                            } else {
                                None
                            }
                        }
                        BinaryOperator::Or => {
                            if !self.evaluator.has_side_effects(binary.left()) {
                                self.evaluator.evaluate(binary.left()).is_truthy().map(
                                    |is_truthy| {
                                        if is_truthy {
                                            binary.left().clone()
                                        } else {
                                            binary.right().clone()
                                        }
                                    },
                                )
                            } else {
                                None
                            }
                        }
                        _ => None,
                    }
                }
            }
            Expression::If(_) => {
                if !self.evaluator.has_side_effects(expression) {
                    self.evaluator.evaluate(expression).to_expression()
                } else {
                    None
                }
            }
            _ => None,
        }
    }
}

impl NodeProcessor for Computer {
    fn process_expression(&mut self, expression: &mut Expression) {
        if let Some(replace_with) = self.replace_with(expression) {
            *expression = replace_with;
        }
    }
}

pub const COMPUTE_EXPRESSIONS_RULE_NAME: &str = "compute_expression";

/// A rule that compute expressions that do not have any side-effects.
#[derive(Debug, Default, PartialEq, Eq)]
pub struct ComputeExpression {}

impl FlawlessRule for ComputeExpression {
    fn flawless_process(&self, block: &mut Block, _: &Context) {
        let mut processor = Computer::default();
        DefaultVisitor::visit_block(block, &mut processor);
    }
}

impl RuleConfiguration for ComputeExpression {
    fn configure(&mut self, properties: RuleProperties) -> Result<(), RuleConfigurationError> {
        verify_no_rule_properties(&properties)?;

        Ok(())
    }

    fn get_name(&self) -> &'static str {
        COMPUTE_EXPRESSIONS_RULE_NAME
    }

    fn serialize_to_properties(&self) -> RuleProperties {
        RuleProperties::new()
    }
}

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

    use insta::assert_json_snapshot;

    fn new_rule() -> ComputeExpression {
        ComputeExpression::default()
    }

    #[test]
    fn serialize_default_rule() {
        let rule: Box<dyn Rule> = Box::new(new_rule());

        assert_json_snapshot!("default_compute_expression", rule);
    }
}