jsonlogic 0.5.1

A JsonLogic implementation in Rust
Documentation 
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use serde_json::{Number, Value};

use super::{logic, Data, Expression};

/// "-", takes two numbers and returns the substraction of the them.
/// If only one argument is passed, returns the negation of that argument.
/// Returns `Value::Null` one of the arguments cannot be coerced into a number.
pub fn compute(args: &[Expression], data: &Data) -> Value {
    let a = match args.get(0).map(|arg| arg.compute(data)) {
        Some(arg) => arg,
        None => return Value::Null,
    };

    match args.get(1).map(|arg| arg.compute(data)) {
        None => compute_negation(&logic::coerce_to_f64(&a)),
        Some(b) => compute_substraction(&logic::coerce_to_f64(&a), &logic::coerce_to_f64(&b)),
    }
}

fn compute_negation(a: &Option<f64>) -> Value {
    match a {
        Some(a) => Value::Number(Number::from_f64(-1f64 * a).unwrap()),
        None => Value::Null,
    }
}

fn compute_substraction(a: &Option<f64>, b: &Option<f64>) -> Value {
    match (a, b) {
        (Some(a), Some(b)) => match Number::from_f64(a - b) {
            Some(num) => Value::Number(num),
            None => Value::Null,
        },
        _ => Value::Null,
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::compute_const;
    use serde_json::json;

    #[test]
    fn null() {
        assert_eq!(compute_const!(), Value::Null);
        assert_eq!(compute_const!(json!("a")), Value::Null);
    }

    #[test]
    fn negation() {
        assert_eq!(compute_const!(json!(1)), json!(-1.0));
        assert_eq!(compute_const!(json!("")), json!(-0.0));
        assert!(logic::is_strict_equal(
            &compute_const!(json!("")),
            &json!(0)
        ));
        assert_eq!(compute_const!(json!("-5")), json!(5.0));
    }

    #[test]
    fn substraction() {
        assert_eq!(compute_const!(json!(1), json!(2)), json!(-1.0));
        assert_eq!(compute_const!(json!(4), json!(2)), json!(2.0));
        assert_eq!(compute_const!(json!(4), json!(-2)), json!(6.0));
    }
}