//! An immutable version of ware. Does not use RefCells, instead
//! relying on the user to return the modified variable in the closure.
//!
//! ## Example
//! ```
//! use ware::im::Ware;
//!
//! fn main() {
//!   let mut chain: Ware<i32> = Ware::new();
//!   chain.wrap(Box::new(|num| num * 10));
//!   chain.wrap(Box::new(|num| num - 2));
//!   let result = chain.run(5);
//!   assert_eq!(result, 48);
//! }
//! ```

/// A middleware chain.
pub struct Ware<T> {
	/// The internal list of middleware functions.
	pub fns: Vec<Box<dyn Fn(T) -> T>>,
}

impl<T> Ware<T> {
	/// Create a new middleware chain with a given type.
	///
	/// # Example
	/// ```
	/// use ware::im::Ware;
	/// let mut chain: Ware<String> = Ware::new();
	/// ```
	pub fn new() -> Ware<T> {
		let vec: Vec<Box<dyn Fn(T) -> T>> = Vec::new();
		Ware { fns: vec }
	}

	/// Add a new middleware function to the internal function list. This function
	/// must be of the `Fn` trait, take the specified type and return the same
	/// specified type. It also has to be boxed for memory safety reasons.
	///
	/// # Example
	/// ```
	/// use ware::im::Ware;
	/// let mut chain: Ware<String> = Ware::new();
	/// chain.wrap(Box::new(|st| {
	///     let mut s = st.clone();
	///     s.push('a');
	///     s
	/// }))
	/// ```
	pub fn wrap(&mut self, func: Box<dyn Fn(T) -> T>) {
		self.fns.push(func);
	}

	/// Run the registered middleware functions with the given value to pass
	/// through. Returns whatever the last registered middleware function
	/// returns.
	pub fn run(&self, arg: T) -> T {
		self.fns.iter().fold(arg, |acc, func| func(acc))
	}
}

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

	#[test]
	fn it_works() {
		let value = 1;
		let mut w: Ware<i32> = Ware::new();
		w.wrap(Box::new(|num| num + 1));
		assert_eq!(w.run(value), 2);
	}

	#[test]
	fn it_is_immutable() {
		let value = 1;
		let closure = |num| {
			let num = num + 1;
			num
		};
		let mut w: Ware<i32> = Ware::new();
		w.wrap(Box::new(closure));
		assert_eq!(w.run(value), 2);
		assert_eq!(value, 1);
	}
}