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

use crate::{
    di::{Asyncify, Injectable, Insert},
    from_fn_with_description, Handler, HandlerDescription,
};
use std::{ops::ControlFlow, sync::Arc};

/// Constructs a handler that optionally passes a value of a new type further.
///
/// If the `proj` function returns `Some(v)` then `v` will be added to the
/// container and passed further in a handler chain. If the function returns
/// `None`, then the handler will return [`ControlFlow::Continue`] with the old
/// container.
#[must_use]
#[track_caller]
pub fn filter_map<'a, Projection, Input, Output, NewType, Args, Descr>(
    proj: Projection,
) -> Handler<'a, Input, Output, Descr>
where
    Input: Clone,
    Asyncify<Projection>: Injectable<Input, Option<NewType>, Args> + Send + Sync + 'a,
    Input: Insert<NewType> + Send + 'a,
    Output: 'a,
    Descr: HandlerDescription,
    NewType: Send,
{
    filter_map_with_description(Descr::filter_map(), proj)
}

/// The asynchronous version of [`filter_map`].
#[must_use]
#[track_caller]
pub fn filter_map_async<'a, Projection, Input, Output, NewType, Args, Descr>(
    proj: Projection,
) -> Handler<'a, Input, Output, Descr>
where
    Input: Clone,
    Projection: Injectable<Input, Option<NewType>, Args> + Send + Sync + 'a,
    Input: Insert<NewType> + Send + 'a,
    Output: 'a,
    Descr: HandlerDescription,
    NewType: Send,
{
    filter_map_async_with_description(Descr::filter_map_async(), proj)
}

/// [`filter_map`] with a custom description.
#[must_use]
pub fn filter_map_with_description<'a, Projection, Input, Output, NewType, Args, Descr>(
    description: Descr,
    proj: Projection,
) -> Handler<'a, Input, Output, Descr>
where
    Input: Clone,
    Asyncify<Projection>: Injectable<Input, Option<NewType>, Args> + Send + Sync + 'a,
    Input: Insert<NewType> + Send + 'a,
    Output: 'a,
    NewType: Send,
{
    filter_map_async_with_description(description, Asyncify(proj))
}

/// [`filter_map_async`] with a custom description.
#[must_use]
pub fn filter_map_async_with_description<'a, Projection, Input, Output, NewType, Args, Descr>(
    description: Descr,
    proj: Projection,
) -> Handler<'a, Input, Output, Descr>
where
    Input: Clone,
    Projection: Injectable<Input, Option<NewType>, Args> + Send + Sync + 'a,
    Input: Insert<NewType> + Send + 'a,
    Output: 'a,
    NewType: Send,
{
    let proj = Arc::new(proj);

    from_fn_with_description(description, move |container: Input, cont| {
        let proj = Arc::clone(&proj);

        async move {
            let proj = proj.inject(&container);
            let res = proj().await;
            std::mem::drop(proj);

            match res {
                Some(new_type) => {
                    let mut intermediate = container.clone();
                    intermediate.insert(new_type);
                    match cont(intermediate).await {
                        ControlFlow::Continue(_) => ControlFlow::Continue(container),
                        ControlFlow::Break(result) => ControlFlow::Break(result),
                    }
                }
                None => ControlFlow::Continue(container),
            }
        }
    })
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{deps, help_inference};

    #[tokio::test]
    async fn test_some() {
        let value = 123;

        let result = help_inference(filter_map(move || Some(value)))
            .endpoint(move |event: i32| async move {
                assert_eq!(event, value);
                value
            })
            .dispatch(deps![])
            .await;

        assert!(result == ControlFlow::Break(value));
    }

    #[tokio::test]
    async fn test_none() {
        let result = help_inference(filter_map(|| None::<i32>))
            .endpoint(|| async move { unreachable!() })
            .dispatch(deps![])
            .await;

        assert!(result == ControlFlow::Continue(crate::deps![]));
    }
}