#[derive(Debug)]
pub struct Stack<T> {
    size: usize,
    data: Vec<T>,
}

impl<T> Stack<T> {
    pub fn new() -> Self {
        Stack {
            size: 0,
            data: Vec::new(),
        }
    }

    pub fn is_empty(&self) -> bool {
        self.size == 0
    }

    pub fn push(&mut self, item: T) {
        self.data.push(item);
        self.size += 1;
    }

    pub fn pop(&mut self) -> Option<T> {
        if self.size == 0 {
            None
        } else {
            self.size -= 1;
            self.data.pop()
        }
    }

    pub fn peek(&self) -> Option<&T> {
        if self.size == 0 {
            None
        } else {
            self.data.last()
        }
    }

    pub fn size(&self) -> usize {
        self.size
    }

    pub fn clear(&mut self) {
        self.data.clear();
    }

    pub fn into_iter(self) -> IntoIter<T> {
        IntoIter(self)
    }

    pub fn iter(&self) -> Iter<T> {
        Iter {
            stack: self.data.iter().collect(),
        }
    }

    pub fn iter_mut(&mut self) -> IterMut<T> {
        IterMut {
            stack: self.data.iter_mut().collect(),
        }
    }
}

pub struct IntoIter<T>(Stack<T>);
impl<T: Clone> Iterator for IntoIter<T> {
    type Item = T;

    fn next(&mut self) -> Option<Self::Item> {
        if self.0.is_empty() {
            None
        } else {
            self.0.size -= 1;
            self.0.data.pop()
        }
    }
}

pub struct Iter<'a, T: 'a> {
    stack: Vec<&'a T>,
}
impl<'a, T> Iterator for Iter<'a, T> {
    type Item = &'a T;

    fn next(&mut self) -> Option<Self::Item> {
        self.stack.pop()
    }
}
pub struct IterMut<'a, T: 'a> {
    stack: Vec<&'a mut T>,
}
impl<'a, T> Iterator for IterMut<'a, T> {
    type Item = &'a mut T;

    fn next(&mut self) -> Option<Self::Item> {
        self.stack.pop()
    }
}

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

    #[test]
    fn test_stack_new() {
        let stack = Stack::<i32>::new();

        assert_eq!(stack.size, 0);
    }
    #[test]
    fn test_stack_is_empty() {
        let stack = Stack::<i32>::new();

        assert!(stack.is_empty());
    }

    #[test]
    fn test_stack_push() {
        let mut stack = Stack::<i32>::new();
        stack.push(1);
        stack.push(2);
        stack.push(3);

        assert_eq!(stack.size, 3);
    }

    #[test]
    fn test_stack_pop() {
        let mut stack = Stack::<i32>::new();
        stack.push(1);
        stack.push(2);
        stack.push(3);

        assert_eq!(stack.pop(), Some(3));
    }

    #[test]
    fn test_stack_peek() {
        let mut stack = Stack::<i32>::new();
        stack.push(1);
        stack.push(2);
        stack.push(3);

        assert_eq!(stack.peek(), Some(&3));
    }

    #[test]
    fn test_stack_into_iter() {
        let mut stack = Stack::<i32>::new();
        stack.push(1);
        stack.push(2);
        stack.push(3);

        let mut iter = stack.into_iter();
        assert_eq!(iter.next(), Some(3));
        assert_eq!(iter.next(), Some(2));
        assert_eq!(iter.next(), Some(1));
        assert_eq!(iter.next(), None);
    }

    #[test]
    fn test_stack_iter() {
        let mut stack = Stack::<i32>::new();
        stack.push(1);
        stack.push(2);
        stack.push(3);

        let mut iter = stack.iter();
        assert_eq!(iter.next(), Some(&3));
        assert_eq!(iter.next(), Some(&2));
        assert_eq!(iter.next(), Some(&1));
        assert_eq!(iter.next(), None);
    }

    #[test]
    fn test_stack_iter_mut() {
        let mut stack = Stack::<i32>::new();
        stack.push(1);
        stack.push(2);
        stack.push(3);

        let mut iter = stack.iter_mut();

        assert_eq!(iter.next(), Some(&mut 3));
        assert_eq!(iter.next(), Some(&mut 2));
        assert_eq!(iter.next(), Some(&mut 1));
    }
}