reval 0.7.9

Simple Rust expression evaluator
Documentation 
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use super::UserFunction;
use crate::{
    expr::keywords::{is_reserved_keyword, is_valid_identifier},
    Error, Result,
};
use std::collections::HashMap;

/// Stores user-functions so they can be easilly called
#[derive(Default)]
pub struct UserFunctions {
    functions: HashMap<&'static str, BoxedFunction>,
}

/// Convenience type for passing around boxed user-function implementations
pub(crate) type BoxedFunction = Box<dyn UserFunction + Send + Sync + 'static>;

impl UserFunctions {
    /// Get a userfunction by name
    pub(crate) fn get(&self, name: &str) -> Result<&BoxedFunction> {
        self.functions
            .get(name)
            .ok_or_else(|| Error::UnknownUserFunction(name.to_owned()))
    }

    /// Add a user-function to the collection
    pub fn add_function(
        &mut self,
        function: impl UserFunction + Send + Sync + 'static,
    ) -> Result<()> {
        self.add_boxed_function(Box::new(function))
    }

    pub(crate) fn add_boxed_function(&mut self, function: BoxedFunction) -> Result<()> {
        let name = function.name();

        if is_reserved_keyword(name) {
            return Err(Error::InvalidFunctionName(name.to_string()));
        }

        if !is_valid_identifier(name) {
            return Err(Error::InvalidFunctionName(name.to_string()));
        }

        if self.functions.contains_key(name) {
            return Err(Error::DuplicateFunctionName(name.to_string()));
        }

        self.functions.insert(name, function);

        Ok(())
    }

    /// Merge two sets of user-functions
    pub fn merge(&mut self, functions: UserFunctions) -> &mut Self {
        self.functions.extend(functions.functions);
        self
    }
}

#[cfg(test)]
mod when_managing_user_functions {
    use super::*;
    use crate::prelude::*;
    use async_trait::async_trait;

    #[test]
    fn should_add_function() {
        let mut functions = UserFunctions::default();

        functions.add_function(func("test_function")).unwrap();
        functions.get("test_function").unwrap();
    }

    #[test]
    fn should_not_add_duplicate_function_name() {
        let mut functions = UserFunctions::default();

        // Add a function
        functions.add_function(func("test_function")).unwrap();

        // Add a function with the same name
        assert!(matches!(
            functions.add_function(func("test_function")),
            Err(Error::DuplicateFunctionName(name)) if name == "test_function".to_string()
        ));
    }

    #[test]
    fn should_not_add_reserved_keyword_as_function_name() {
        let mut functions = UserFunctions::default();

        // Add a function with the same name
        assert!(matches!(
            functions.add_function(func("if")),
            Err(Error::InvalidFunctionName(name)) if name == "if".to_string()
        ));
    }

    fn func(name: &'static str) -> TestFunc {
        TestFunc { name }
    }

    struct TestFunc {
        name: &'static str,
    }

    #[async_trait]
    impl UserFunction for TestFunc {
        async fn call(&self, _params: Value) -> FunctionResult {
            Ok(Value::None)
        }

        fn name(&self) -> &'static str {
            self.name
        }
    }
}