// box1.rs
//
// At compile time, Rust needs to know how much space a type takes up. This becomes problematic
// for recursive types, where a value can have as part of itself another value of the same type.
// To get around the issue, we can use a `Box` - a smart pointer used to store data on the heap,
// which also allows us to wrap a recursive type.
//
// The recursive type we're implementing in this exercise is the `cons list` - a data structure
// frequently found in functional programming languages. Each item in a cons list contains two
// elements: the value of the current item and the next item. The last item is a value called `Nil`.
//
// Step 1: use a `Box` in the enum definition to make the code compile
// Step 2: create both empty and non-empty cons lists by replacing `todo!()`
//
// Note: the tests should not be changed
//
// Execute `rustlings hint box1` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

#[derive(PartialEq, Debug)]
pub enum List {
    Cons(i32, List),
    Nil,
}

fn main() {
    println!("This is an empty cons list: {:?}", create_empty_list());
    println!(
        "This is a non-empty cons list: {:?}",
        create_non_empty_list()
    );
    // convert unit tests to main
    fn test_create_empty_list() {
        assert_eq!(List::Nil, create_empty_list())
    }

    fn test_create_non_empty_list() {
        assert_ne!(create_empty_list(), create_non_empty_list())
    }
    test_create_empty_list();
    test_create_non_empty_list();
}

pub fn create_empty_list() -> List {
    todo!()
}

pub fn create_non_empty_list() -> List {
    todo!()
}


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

    #[test]
    fn test_create_empty_list() {
        assert_eq!(List::Nil, create_empty_list())
    }

    #[test]
    fn test_create_non_empty_list() {
        assert_ne!(create_empty_list(), create_non_empty_list())
    }
}

// cow1.rs

// This exercise explores the Cow, or Clone-On-Write type.
// Cow is a clone-on-write smart pointer.
// It can enclose and provide immutable access to borrowed data, and clone the data lazily when mutation or ownership is required.
// The type is designed to work with general borrowed data via the Borrow trait.
//
// This exercise is meant to show you what to expect when passing data to Cow.
// Fix the unit tests by checking for Cow::Owned(_) and Cow::Borrowed(_) at the TODO markers.

// I AM NOT DONE

use std::borrow::Cow;

fn abs_all<'a, 'b>(input: &'a mut Cow<'b, [i32]>) -> &'a mut Cow<'b, [i32]> {
    for i in 0..input.len() {
        let v = input[i];
        if v < 0 {
            // Clones into a vector if not already owned.
            input.to_mut()[i] = -v;
        }
    }
    input
}

// convert unit tests to main
fn main() {
    fn reference_mutation() -> Result<(), &'static str> {
        // Clone occurs because `input` needs to be mutated.
        let slice = [-1, 0, 1];
        let mut input = Cow::from(&slice[..]);
        match abs_all(&mut input) {
            Cow::Owned(_) => Ok(()),
            _ => Err("Expected owned value"),
        }
    }

    fn reference_no_mutation() -> Result<(), &'static str> {
        // No clone occurs because `input` doesn't need to be mutated.
        let slice = [0, 1, 2];
        let mut input = Cow::from(&slice[..]);
        match abs_all(&mut input) {
            // TODO
        }
    }

    fn owned_no_mutation() -> Result<(), &'static str> {
        // We can also pass `slice` without `&` so Cow owns it directly.
        // In this case no mutation occurs and thus also no clone,
        // but the result is still owned because it always was.
        let slice = vec![0, 1, 2];
        let mut input = Cow::from(slice);
        match abs_all(&mut input) {
            // TODO
        }
    }

    fn owned_mutation() -> Result<(), &'static str> {
        // Of course this is also the case if a mutation does occur.
        // In this case the call to `to_mut()` returns a reference to
        // the same data as before.
        let slice = vec![-1, 0, 1];
        let mut input = Cow::from(slice);
        match abs_all(&mut input) {
            // TODO
        }
    }
    reference_mutation();
    reference_no_mutation();
    owned_no_mutation();
    owned_mutation();
}


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

    #[test]
    fn reference_mutation() -> Result<(), &'static str> {
        // Clone occurs because `input` needs to be mutated.
        let slice = [-1, 0, 1];
        let mut input = Cow::from(&slice[..]);
        match abs_all(&mut input) {
            Cow::Owned(_) => Ok(()),
            _ => Err("Expected owned value"),
        }
    }

    #[test]
    fn reference_no_mutation() -> Result<(), &'static str> {
        // No clone occurs because `input` doesn't need to be mutated.
        let slice = [0, 1, 2];
        let mut input = Cow::from(&slice[..]);
        match abs_all(&mut input) {
            // TODO
        }
    }

    #[test]
    fn owned_no_mutation() -> Result<(), &'static str> {
        // We can also pass `slice` without `&` so Cow owns it directly.
        // In this case no mutation occurs and thus also no clone,
        // but the result is still owned because it always was.
        let slice = vec![0, 1, 2];
        let mut input = Cow::from(slice);
        match abs_all(&mut input) {
            // TODO
        }
    }

    #[test]
    fn owned_mutation() -> Result<(), &'static str> {
        // Of course this is also the case if a mutation does occur.
        // In this case the call to `to_mut()` returns a reference to
        // the same data as before.
        let slice = vec![-1, 0, 1];
        let mut input = Cow::from(slice);
        match abs_all(&mut input) {
            // TODO
        }
    }
}

// rc1.rs
// In this exercise, we want to express the concept of multiple owners via the Rc<T> type.
// This is a model of our solar system - there is a Sun type and multiple Planets.
// The Planets take ownership of the sun, indicating that they revolve around the sun.

// Make this code compile by using the proper Rc primitives to express that the sun has multiple owners.

// I AM NOT DONE

use std::rc::Rc;

#[derive(Debug)]
struct Sun {}

#[derive(Debug)]
enum Planet {
    Mercury(Rc<Sun>),
    Venus(Rc<Sun>),
    Earth(Rc<Sun>),
    Mars(Rc<Sun>),
    Jupiter(Rc<Sun>),
    Saturn(Rc<Sun>),
    Uranus(Rc<Sun>),
    Neptune(Rc<Sun>),
}

impl Planet {
    fn details(&self) {
        println!("Hi from {:?}!", self)
    }
}

fn main() {
    let sun = Rc::new(Sun {});
    println!("reference count = {}", Rc::strong_count(&sun)); // 1 reference

    let mercury = Planet::Mercury(Rc::clone(&sun));
    println!("reference count = {}", Rc::strong_count(&sun)); // 2 references
    mercury.details();

    let venus = Planet::Venus(Rc::clone(&sun));
    println!("reference count = {}", Rc::strong_count(&sun)); // 3 references
    venus.details();

    let earth = Planet::Earth(Rc::clone(&sun));
    println!("reference count = {}", Rc::strong_count(&sun)); // 4 references
    earth.details();

    let mars = Planet::Mars(Rc::clone(&sun));
    println!("reference count = {}", Rc::strong_count(&sun)); // 5 references
    mars.details();

    let jupiter = Planet::Jupiter(Rc::clone(&sun));
    println!("reference count = {}", Rc::strong_count(&sun)); // 6 references
    jupiter.details();

    // TODO
    let saturn = Planet::Saturn(Rc::new(Sun {}));
    println!("reference count = {}", Rc::strong_count(&sun)); // 7 references
    saturn.details();

    // TODO
    let uranus = Planet::Uranus(Rc::new(Sun {}));
    println!("reference count = {}", Rc::strong_count(&sun)); // 8 references
    uranus.details();

    // TODO
    let neptune = Planet::Neptune(Rc::new(Sun {}));
    println!("reference count = {}", Rc::strong_count(&sun)); // 9 references
    neptune.details();

    assert_eq!(Rc::strong_count(&sun), 9);

    drop(neptune);
    println!("reference count = {}", Rc::strong_count(&sun)); // 8 references

    drop(uranus);
    println!("reference count = {}", Rc::strong_count(&sun)); // 7 references

    drop(saturn);
    println!("reference count = {}", Rc::strong_count(&sun)); // 6 references

    drop(jupiter);
    println!("reference count = {}", Rc::strong_count(&sun)); // 5 references

    drop(mars);
    println!("reference count = {}", Rc::strong_count(&sun)); // 4 references

    // TODO
    println!("reference count = {}", Rc::strong_count(&sun)); // 3 references

    // TODO
    println!("reference count = {}", Rc::strong_count(&sun)); // 2 references

    // TODO
    println!("reference count = {}", Rc::strong_count(&sun)); // 1 reference

    assert_eq!(Rc::strong_count(&sun), 1);
}

use std::rc::Rc;

struct Node {
    value: i32,
    parent: Option<Rc<Node>>,
    children: Vec<Rc<Node>>,
}

impl Node {
    fn new(value: i32) -> Rc<Self> {
        Rc::new(Self {
            value,
            parent: None,
            children: Vec::new(),
        })
    }

    fn add_child(&mut self, child: Rc<Self>) {
        self.children.push(child);
        child.parent = Some(Rc::clone(&self));
    }
}

fn main() {
    let root = Node::new(0);
    let child1 = Node::new(1);
    let child2 = Node::new(2);
    child1.add_child(Rc::clone(&child2));
    child2.add_child(Rc::clone(&child1));
    root.add_child(child1);
    root.add_child(child2);
    println!("{}", root.value);
}