// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

/*!

A doubly-linked list. Supports O(1) head, tail, count, push, pop, etc.

# Safety note

Do not use ==, !=, <, etc on doubly-linked lists -- it may not terminate.

*/

use core::prelude::*;

use core::managed;

pub type DListLink<T> = Option<@mut DListNode<T>>;

pub struct DListNode<T> {
    data: T,
    linked: bool, // for assertions
    prev: DListLink<T>,
    next: DListLink<T>,
}

pub struct DList<T> {
    size: uint,
    hd: DListLink<T>,
    tl: DListLink<T>,
}

priv impl<T> DListNode<T> {
    fn assert_links(@mut self) {
        match self.next {
            Some(neighbour) => match neighbour.prev {
              Some(me) => if !managed::mut_ptr_eq(self, me) {
                  fail!("Asymmetric next-link in dlist node.")
              },
              None => fail!("One-way next-link in dlist node.")
            },
            None => ()
        }
        match self.prev {
            Some(neighbour) => match neighbour.next {
              Some(me) => if !managed::mut_ptr_eq(me, self) {
                  fail!("Asymmetric prev-link in dlist node.")
              },
              None => fail!("One-way prev-link in dlist node.")
            },
            None => ()
        }
    }
}

pub impl<T> DListNode<T> {
    /// Get the next node in the list, if there is one.
    fn next_link(@mut self) -> DListLink<T> {
        self.assert_links();
        self.next
    }
    /// Get the next node in the list, failing if there isn't one.
    fn next_node(@mut self) -> @mut DListNode<T> {
        match self.next_link() {
            Some(nobe) => nobe,
            None       => fail!("This dlist node has no next neighbour.")
        }
    }
    /// Get the previous node in the list, if there is one.
    fn prev_link(@mut self) -> DListLink<T> {
        self.assert_links();
        self.prev
    }
    /// Get the previous node in the list, failing if there isn't one.
    fn prev_node(@mut self) -> @mut DListNode<T> {
        match self.prev_link() {
            Some(nobe) => nobe,
            None       => fail!("This dlist node has no previous neighbour.")
        }
    }
}

/// Creates a new dlist node with the given data.
pub fn new_dlist_node<T>(data: T) -> @mut DListNode<T> {
    @mut DListNode { data: data, linked: false, prev: None, next: None }
}

/// Creates a new, empty dlist.
pub fn DList<T>() -> @mut DList<T> {
    @mut DList { size: 0, hd: None, tl: None }
}

/// Creates a new dlist with a single element
pub fn from_elem<T>(data: T) -> @mut DList<T> {
    let list = DList();
    list.push(data);
    list
}

pub fn from_vec<T:Copy>(vec: &[T]) -> @mut DList<T> {
    do vec::foldl(DList(), vec) |list,data| {
        list.push(*data); // Iterating left-to-right -- add newly to the tail.
        list
    }
}

/// Produce a list from a list of lists, leaving no elements behind in the
/// input. O(number of sub-lists).
pub fn concat<T>(lists: @mut DList<@mut DList<T>>) -> @mut DList<T> {
    let result = DList();
    while !lists.is_empty() {
        result.append(lists.pop().get());
    }
    result
}

priv impl<T> DList<T> {
    fn new_link(data: T) -> DListLink<T> {
        Some(@mut DListNode {
            data: data,
            linked: true,
            prev: None,
            next: None
        })
    }
    fn assert_mine(@mut self, nobe: @mut DListNode<T>) {
        // These asserts could be stronger if we had node-root back-pointers,
        // but those wouldn't allow for O(1) append.
        if self.size == 0 {
            fail!("This dlist is empty; that node can't be on it.")
        }
        if !nobe.linked { fail!("That node isn't linked to any dlist.") }
        if !((nobe.prev.is_some()
              || managed::mut_ptr_eq(self.hd.expect("headless dlist?"),
                                 nobe)) &&
             (nobe.next.is_some()
              || managed::mut_ptr_eq(self.tl.expect("tailless dlist?"),
                                 nobe))) {
            fail!("That node isn't on this dlist.")
        }
    }
    fn make_mine(&self, nobe: @mut DListNode<T>) {
        if nobe.prev.is_some() || nobe.next.is_some() || nobe.linked {
            fail!("Cannot insert node that's already on a dlist!")
        }
        nobe.linked = true;
    }
    // Link two nodes together. If either of them are 'none', also sets
    // the head and/or tail pointers appropriately.
    #[inline(always)]
    fn link(&mut self, before: DListLink<T>, after: DListLink<T>) {
        match before {
            Some(neighbour) => neighbour.next = after,
            None            => self.hd        = after
        }
        match after {
            Some(neighbour) => neighbour.prev = before,
            None            => self.tl        = before
        }
    }
    // Remove a node from the list.
    fn unlink(@mut self, nobe: @mut DListNode<T>) {
        self.assert_mine(nobe);
        assert!(self.size > 0);
        self.link(nobe.prev, nobe.next);
        nobe.prev = None; // Release extraneous references.
        nobe.next = None;
        nobe.linked = false;
        self.size -= 1;
    }

    fn add_head(@mut self, nobe: DListLink<T>) {
        self.link(nobe, self.hd); // Might set tail too.
        self.hd = nobe;
        self.size += 1;
    }
    fn add_tail(@mut self, nobe: DListLink<T>) {
        self.link(self.tl, nobe); // Might set head too.
        self.tl = nobe;
        self.size += 1;
    }
    fn insert_left(@mut self,
                   nobe: DListLink<T>,
                   neighbour: @mut DListNode<T>) {
        self.assert_mine(neighbour);
        assert!(self.size > 0);
        self.link(neighbour.prev, nobe);
        self.link(nobe, Some(neighbour));
        self.size += 1;
    }
    fn insert_right(@mut self,
                    neighbour: @mut DListNode<T>,
                    nobe: DListLink<T>) {
        self.assert_mine(neighbour);
        assert!(self.size > 0);
        self.link(nobe, neighbour.next);
        self.link(Some(neighbour), nobe);
        self.size += 1;
    }
}

pub impl<T> DList<T> {
    /// Get the size of the list. O(1).
    fn len(@mut self) -> uint { self.size }
    /// Returns true if the list is empty. O(1).
    fn is_empty(@mut self) -> bool { self.len() == 0 }

    /// Add data to the head of the list. O(1).
    fn push_head(@mut self, data: T) {
        self.add_head(DList::new_link(data));
    }
    /**
     * Add data to the head of the list, and get the new containing
     * node. O(1).
     */
    fn push_head_n(@mut self, data: T) -> @mut DListNode<T> {
        let nobe = DList::new_link(data);
        self.add_head(nobe);
        nobe.get()
    }
    /// Add data to the tail of the list. O(1).
    fn push(@mut self, data: T) {
        self.add_tail(DList::new_link(data));
    }
    /**
     * Add data to the tail of the list, and get the new containing
     * node. O(1).
     */
    fn push_n(@mut self, data: T) -> @mut DListNode<T> {
        let nobe = DList::new_link(data);
        self.add_tail(nobe);
        nobe.get()
    }
    /**
     * Insert data into the middle of the list, left of the given node.
     * O(1).
     */
    fn insert_before(@mut self, data: T, neighbour: @mut DListNode<T>) {
        self.insert_left(DList::new_link(data), neighbour);
    }
    /**
     * Insert an existing node in the middle of the list, left of the
     * given node. O(1).
     */
    fn insert_n_before(@mut self,
                       nobe: @mut DListNode<T>,
                       neighbour: @mut DListNode<T>) {
        self.make_mine(nobe);
        self.insert_left(Some(nobe), neighbour);
    }
    /**
     * Insert data in the middle of the list, left of the given node,
     * and get its containing node. O(1).
     */
    fn insert_before_n(
        @mut self,
        data: T,
        neighbour: @mut DListNode<T>
    ) -> @mut DListNode<T> {
        let nobe = DList::new_link(data);
        self.insert_left(nobe, neighbour);
        nobe.get()
    }
    /**
     * Insert data into the middle of the list, right of the given node.
     * O(1).
     */
    fn insert_after(@mut self, data: T, neighbour: @mut DListNode<T>) {
        self.insert_right(neighbour, DList::new_link(data));
    }
    /**
     * Insert an existing node in the middle of the list, right of the
     * given node. O(1).
     */
    fn insert_n_after(@mut self,
                      nobe: @mut DListNode<T>,
                      neighbour: @mut DListNode<T>) {
        self.make_mine(nobe);
        self.insert_right(neighbour, Some(nobe));
    }
    /**
     * Insert data in the middle of the list, right of the given node,
     * and get its containing node. O(1).
     */
    fn insert_after_n(
        @mut self,
        data: T,
        neighbour: @mut DListNode<T>
    ) -> @mut DListNode<T> {
        let nobe = DList::new_link(data);
        self.insert_right(neighbour, nobe);
        nobe.get()
    }

    /// Remove a node from the head of the list. O(1).
    fn pop_n(@mut self) -> DListLink<T> {
        let hd = self.peek_n();
        hd.map(|nobe| self.unlink(*nobe));
        hd
    }
    /// Remove a node from the tail of the list. O(1).
    fn pop_tail_n(@mut self) -> DListLink<T> {
        let tl = self.peek_tail_n();
        tl.map(|nobe| self.unlink(*nobe));
        tl
    }
    /// Get the node at the list's head. O(1).
    fn peek_n(@mut self) -> DListLink<T> { self.hd }
    /// Get the node at the list's tail. O(1).
    fn peek_tail_n(@mut self) -> DListLink<T> { self.tl }

    /// Get the node at the list's head, failing if empty. O(1).
    fn head_n(@mut self) -> @mut DListNode<T> {
        match self.hd {
            Some(nobe) => nobe,
            None       => fail!("Attempted to get the head of an empty dlist.")
        }
    }
    /// Get the node at the list's tail, failing if empty. O(1).
    fn tail_n(@mut self) -> @mut DListNode<T> {
        match self.tl {
            Some(nobe) => nobe,
            None       => fail!("Attempted to get the tail of an empty dlist.")
        }
    }

    /// Remove a node from anywhere in the list. O(1).
    fn remove(@mut self, nobe: @mut DListNode<T>) { self.unlink(nobe); }

    /**
     * Empty another list onto the end of this list, joining this list's tail
     * to the other list's head. O(1).
     */
    fn append(@mut self, them: @mut DList<T>) {
        if managed::mut_ptr_eq(self, them) {
            fail!("Cannot append a dlist to itself!")
        }
        if them.len() > 0 {
            self.link(self.tl, them.hd);
            self.tl    = them.tl;
            self.size += them.size;
            them.size  = 0;
            them.hd    = None;
            them.tl    = None;
        }
    }
    /**
     * Empty another list onto the start of this list, joining the other
     * list's tail to this list's head. O(1).
     */
    fn prepend(@mut self, them: @mut DList<T>) {
        if managed::mut_ptr_eq(self, them) {
            fail!("Cannot prepend a dlist to itself!")
        }
        if them.len() > 0 {
            self.link(them.tl, self.hd);
            self.hd    = them.hd;
            self.size += them.size;
            them.size  = 0;
            them.hd    = None;
            them.tl    = None;
        }
    }

    /// Reverse the list's elements in place. O(n).
    fn reverse(@mut self) {
        do self.hd.while_some |nobe| {
            let next_nobe = nobe.next;
            self.remove(nobe);
            self.make_mine(nobe);
            self.add_head(Some(nobe));
            next_nobe
        }
    }

    /**
     * Remove everything from the list. This is important because the cyclic
     * links won't otherwise be automatically refcounted-collected. O(n).
     */
    fn clear(@mut self) {
        // Cute as it would be to simply detach the list and proclaim "O(1)!",
        // the GC would still be a hidden O(n). Better to be honest about it.
        while !self.is_empty() {
            let _ = self.pop_n();
        }
    }

    /// Iterate over nodes.
    fn each_node(@mut self, f: &fn(@mut DListNode<T>) -> bool) -> bool {
        let mut link = self.peek_n();
        while link.is_some() {
            let nobe = link.get();
            if !f(nobe) { return false; }
            link = nobe.next_link();
        }
        return true;
    }

    /// Check data structure integrity. O(n).
    fn assert_consistent(@mut self) {
        if self.hd.is_none() || self.tl.is_none() {
            assert!(self.hd.is_none() && self.tl.is_none());
        }
        // iterate forwards
        let mut count = 0;
        let mut link = self.peek_n();
        let mut rabbit = link;
        while link.is_some() {
            let nobe = link.get();
            assert!(nobe.linked);
            // check cycle
            if rabbit.is_some() {
                rabbit = rabbit.get().next;
            }
            if rabbit.is_some() {
                rabbit = rabbit.get().next;
            }
            if rabbit.is_some() {
                assert!(!managed::mut_ptr_eq(rabbit.get(), nobe));
            }
            // advance
            link = nobe.next_link();
            count += 1;
        }
        assert_eq!(count, self.len());
        // iterate backwards - some of this is probably redundant.
        link = self.peek_tail_n();
        rabbit = link;
        while link.is_some() {
            let nobe = link.get();
            assert!(nobe.linked);
            // check cycle
            if rabbit.is_some() {
                rabbit = rabbit.get().prev;
            }
            if rabbit.is_some() {
                rabbit = rabbit.get().prev;
            }
            if rabbit.is_some() {
                assert!(!managed::mut_ptr_eq(rabbit.get(), nobe));
            }
            // advance
            link = nobe.prev_link();
            count -= 1;
        }
        assert_eq!(count, 0);
    }
}

pub impl<T:Copy> DList<T> {
    /// Remove data from the head of the list. O(1).
    fn pop(@mut self) -> Option<T> {
        self.pop_n().map(|nobe| nobe.data)
    }

    /// Remove data from the tail of the list. O(1).
    fn pop_tail(@mut self) -> Option<T> {
        self.pop_tail_n().map(|nobe| nobe.data)
    }

    /// Get data at the list's head. O(1).
    fn peek(@mut self) -> Option<T> {
        self.peek_n().map(|nobe| nobe.data)
    }

    /// Get data at the list's tail. O(1).
    fn peek_tail(@mut self) -> Option<T> {
        self.peek_tail_n().map (|nobe| nobe.data)
    }

    /// Get data at the list's head, failing if empty. O(1).
    fn head(@mut self) -> T { self.head_n().data }

    /// Get data at the list's tail, failing if empty. O(1).
    fn tail(@mut self) -> T { self.tail_n().data }

    /// Get the elements of the list as a vector. O(n).
    fn to_vec(@mut self) -> ~[T] {
        let mut v = vec::with_capacity(self.size);
        for old_iter::eachi(&self) |index,data| {
            v[index] = *data;
        }
        v
    }
}

impl<T> BaseIter<T> for @mut DList<T> {
    /**
     * Iterates through the current contents.
     *
     * Attempts to access this dlist during iteration are allowed (to
     * allow for e.g. breadth-first search with in-place enqueues), but
     * removing the current node is forbidden.
     */
    fn each(&self, f: &fn(v: &T) -> bool) -> bool {
        let mut link = self.peek_n();
        while link.is_some() {
            let nobe = link.get();
            assert!(nobe.linked);

            {
                let frozen_nobe = &*nobe;
                if !f(&frozen_nobe.data) { return false; }
            }

            // Check (weakly) that the user didn't do a remove.
            if self.size == 0 {
                fail!("The dlist became empty during iteration??")
            }
            if !nobe.linked ||
                (!((nobe.prev.is_some()
                    || managed::mut_ptr_eq(self.hd.expect("headless dlist?"),
                                           nobe))
                   && (nobe.next.is_some()
                    || managed::mut_ptr_eq(self.tl.expect("tailless dlist?"),
                                           nobe)))) {
                fail!("Removing a dlist node during iteration is forbidden!")
            }
            link = nobe.next_link();
        }
        return true;
    }

    #[inline(always)]
    fn size_hint(&self) -> Option<uint> { Some(self.len()) }
}

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

    use super::*;

    #[test]
    fn test_dlist_concat() {
        let a = from_vec([1,2]);
        let b = from_vec([3,4]);
        let c = from_vec([5,6]);
        let d = from_vec([7,8]);
        let ab = from_vec([a,b]);
        let cd = from_vec([c,d]);
        let abcd = concat(concat(from_vec([ab,cd])));
        abcd.assert_consistent(); assert_eq!(abcd.len(), 8);
        abcd.assert_consistent(); assert_eq!(abcd.pop().get(), 1);
        abcd.assert_consistent(); assert_eq!(abcd.pop().get(), 2);
        abcd.assert_consistent(); assert_eq!(abcd.pop().get(), 3);
        abcd.assert_consistent(); assert_eq!(abcd.pop().get(), 4);
        abcd.assert_consistent(); assert_eq!(abcd.pop().get(), 5);
        abcd.assert_consistent(); assert_eq!(abcd.pop().get(), 6);
        abcd.assert_consistent(); assert_eq!(abcd.pop().get(), 7);
        abcd.assert_consistent(); assert_eq!(abcd.pop().get(), 8);
        abcd.assert_consistent(); assert!(abcd.is_empty());
    }
    #[test]
    fn test_dlist_append() {
        let a = from_vec([1,2,3]);
        let b = from_vec([4,5,6]);
        a.append(b);
        assert_eq!(a.len(), 6);
        assert_eq!(b.len(), 0);
        b.assert_consistent();
        a.assert_consistent(); assert_eq!(a.pop().get(), 1);
        a.assert_consistent(); assert_eq!(a.pop().get(), 2);
        a.assert_consistent(); assert_eq!(a.pop().get(), 3);
        a.assert_consistent(); assert_eq!(a.pop().get(), 4);
        a.assert_consistent(); assert_eq!(a.pop().get(), 5);
        a.assert_consistent(); assert_eq!(a.pop().get(), 6);
        a.assert_consistent(); assert!(a.is_empty());
    }
    #[test]
    fn test_dlist_append_empty() {
        let a = from_vec([1,2,3]);
        let b = DList::<int>();
        a.append(b);
        assert_eq!(a.len(), 3);
        assert_eq!(b.len(), 0);
        b.assert_consistent();
        a.assert_consistent(); assert_eq!(a.pop().get(), 1);
        a.assert_consistent(); assert_eq!(a.pop().get(), 2);
        a.assert_consistent(); assert_eq!(a.pop().get(), 3);
        a.assert_consistent(); assert!(a.is_empty());
    }
    #[test]
    fn test_dlist_append_to_empty() {
        let a = DList::<int>();
        let b = from_vec([4,5,6]);
        a.append(b);
        assert_eq!(a.len(), 3);
        assert_eq!(b.len(), 0);
        b.assert_consistent();
        a.assert_consistent(); assert_eq!(a.pop().get(), 4);
        a.assert_consistent(); assert_eq!(a.pop().get(), 5);
        a.assert_consistent(); assert_eq!(a.pop().get(), 6);
        a.assert_consistent(); assert!(a.is_empty());
    }
    #[test]
    fn test_dlist_append_two_empty() {
        let a = DList::<int>();
        let b = DList::<int>();
        a.append(b);
        assert_eq!(a.len(), 0);
        assert_eq!(b.len(), 0);
        b.assert_consistent();
        a.assert_consistent();
    }
    #[test]
    #[ignore(cfg(windows))]
    #[should_fail]
    fn test_dlist_append_self() {
        let a = DList::<int>();
        a.append(a);
    }
    #[test]
    #[ignore(cfg(windows))]
    #[should_fail]
    fn test_dlist_prepend_self() {
        let a = DList::<int>();
        a.prepend(a);
    }
    #[test]
    fn test_dlist_prepend() {
        let a = from_vec([1,2,3]);
        let b = from_vec([4,5,6]);
        b.prepend(a);
        assert_eq!(a.len(), 0);
        assert_eq!(b.len(), 6);
        a.assert_consistent();
        b.assert_consistent(); assert_eq!(b.pop().get(), 1);
        b.assert_consistent(); assert_eq!(b.pop().get(), 2);
        b.assert_consistent(); assert_eq!(b.pop().get(), 3);
        b.assert_consistent(); assert_eq!(b.pop().get(), 4);
        b.assert_consistent(); assert_eq!(b.pop().get(), 5);
        b.assert_consistent(); assert_eq!(b.pop().get(), 6);
        b.assert_consistent(); assert!(b.is_empty());
    }
    #[test]
    fn test_dlist_reverse() {
        let a = from_vec([5,4,3,2,1]);
        a.reverse();
        assert_eq!(a.len(), 5);
        a.assert_consistent(); assert_eq!(a.pop().get(), 1);
        a.assert_consistent(); assert_eq!(a.pop().get(), 2);
        a.assert_consistent(); assert_eq!(a.pop().get(), 3);
        a.assert_consistent(); assert_eq!(a.pop().get(), 4);
        a.assert_consistent(); assert_eq!(a.pop().get(), 5);
        a.assert_consistent(); assert!(a.is_empty());
    }
    #[test]
    fn test_dlist_reverse_empty() {
        let a = DList::<int>();
        a.reverse();
        assert_eq!(a.len(), 0);
        a.assert_consistent();
    }
    #[test]
    fn test_dlist_each_node() {
        let a = from_vec([1,2,4,5]);
        for a.each_node |nobe| {
            if nobe.data > 3 {
                a.insert_before(3, nobe);
            }
        }
        assert_eq!(a.len(), 6);
        a.assert_consistent(); assert_eq!(a.pop().get(), 1);
        a.assert_consistent(); assert_eq!(a.pop().get(), 2);
        a.assert_consistent(); assert_eq!(a.pop().get(), 3);
        a.assert_consistent(); assert_eq!(a.pop().get(), 4);
        a.assert_consistent(); assert_eq!(a.pop().get(), 3);
        a.assert_consistent(); assert_eq!(a.pop().get(), 5);
        a.assert_consistent(); assert!(a.is_empty());
    }
    #[test]
    fn test_dlist_clear() {
        let a = from_vec([5,4,3,2,1]);
        a.clear();
        assert_eq!(a.len(), 0);
        a.assert_consistent();
    }
    #[test]
    fn test_dlist_is_empty() {
        let empty = DList::<int>();
        let full1 = from_vec([1,2,3]);
        assert!(empty.is_empty());
        assert!(!full1.is_empty());
    }
    #[test]
    fn test_dlist_head_tail() {
        let l = from_vec([1,2,3]);
        assert_eq!(l.head(), 1);
        assert_eq!(l.tail(), 3);
        assert_eq!(l.len(), 3);
    }
    #[test]
    fn test_dlist_pop() {
        let l = from_vec([1,2,3]);
        assert_eq!(l.pop().get(), 1);
        assert_eq!(l.tail(), 3);
        assert_eq!(l.head(), 2);
        assert_eq!(l.pop().get(), 2);
        assert_eq!(l.tail(), 3);
        assert_eq!(l.head(), 3);
        assert_eq!(l.pop().get(), 3);
        assert!(l.is_empty());
        assert!(l.pop().is_none());
    }
    #[test]
    fn test_dlist_pop_tail() {
        let l = from_vec([1,2,3]);
        assert_eq!(l.pop_tail().get(), 3);
        assert_eq!(l.tail(), 2);
        assert_eq!(l.head(), 1);
        assert_eq!(l.pop_tail().get(), 2);
        assert_eq!(l.tail(), 1);
        assert_eq!(l.head(), 1);
        assert_eq!(l.pop_tail().get(), 1);
        assert!(l.is_empty());
        assert!(l.pop_tail().is_none());
    }
    #[test]
    fn test_dlist_push() {
        let l = DList::<int>();
        l.push(1);
        assert_eq!(l.head(), 1);
        assert_eq!(l.tail(), 1);
        l.push(2);
        assert_eq!(l.head(), 1);
        assert_eq!(l.tail(), 2);
        l.push(3);
        assert_eq!(l.head(), 1);
        assert_eq!(l.tail(), 3);
        assert_eq!(l.len(), 3);
    }
    #[test]
    fn test_dlist_push_head() {
        let l = DList::<int>();
        l.push_head(3);
        assert_eq!(l.head(), 3);
        assert_eq!(l.tail(), 3);
        l.push_head(2);
        assert_eq!(l.head(), 2);
        assert_eq!(l.tail(), 3);
        l.push_head(1);
        assert_eq!(l.head(), 1);
        assert_eq!(l.tail(), 3);
        assert_eq!(l.len(), 3);
    }
    #[test]
    fn test_dlist_foldl() {
        let l = from_vec(vec::from_fn(101, |x|x));
        assert_eq!(old_iter::foldl(&l, 0, |accum,elem| *accum+*elem), 5050);
    }
    #[test]
    fn test_dlist_break_early() {
        let l = from_vec([1,2,3,4,5]);
        let mut x = 0;
        for l.each |i| {
            x += 1;
            if (*i == 3) { break; }
        }
        assert_eq!(x, 3);
    }
    #[test]
    fn test_dlist_remove_head() {
        let l = DList::<int>();
        l.assert_consistent(); let one = l.push_n(1);
        l.assert_consistent(); let _two = l.push_n(2);
        l.assert_consistent(); let _three = l.push_n(3);
        l.assert_consistent(); assert_eq!(l.len(), 3);
        l.assert_consistent(); l.remove(one);
        l.assert_consistent(); assert_eq!(l.len(), 2);
        l.assert_consistent(); assert_eq!(l.head(), 2);
        l.assert_consistent(); assert_eq!(l.tail(), 3);
        l.assert_consistent(); assert_eq!(l.pop().get(), 2);
        l.assert_consistent(); assert_eq!(l.pop().get(), 3);
        l.assert_consistent(); assert!(l.is_empty());
    }
    #[test]
    fn test_dlist_remove_mid() {
        let l = DList::<int>();
        l.assert_consistent(); let _one = l.push_n(1);
        l.assert_consistent(); let two = l.push_n(2);
        l.assert_consistent(); let _three = l.push_n(3);
        l.assert_consistent(); assert_eq!(l.len(), 3);
        l.assert_consistent(); l.remove(two);
        l.assert_consistent(); assert_eq!(l.len(), 2);
        l.assert_consistent(); assert_eq!(l.head(), 1);
        l.assert_consistent(); assert_eq!(l.tail(), 3);
        l.assert_consistent(); assert_eq!(l.pop().get(), 1);
        l.assert_consistent(); assert_eq!(l.pop().get(), 3);
        l.assert_consistent(); assert!(l.is_empty());
    }
    #[test]
    fn test_dlist_remove_tail() {
        let l = DList::<int>();
        l.assert_consistent(); let _one = l.push_n(1);
        l.assert_consistent(); let _two = l.push_n(2);
        l.assert_consistent(); let three = l.push_n(3);
        l.assert_consistent(); assert_eq!(l.len(), 3);
        l.assert_consistent(); l.remove(three);
        l.assert_consistent(); assert_eq!(l.len(), 2);
        l.assert_consistent(); assert_eq!(l.head(), 1);
        l.assert_consistent(); assert_eq!(l.tail(), 2);
        l.assert_consistent(); assert_eq!(l.pop().get(), 1);
        l.assert_consistent(); assert_eq!(l.pop().get(), 2);
        l.assert_consistent(); assert!(l.is_empty());
    }
    #[test]
    fn test_dlist_remove_one_two() {
        let l = DList::<int>();
        l.assert_consistent(); let one = l.push_n(1);
        l.assert_consistent(); let two = l.push_n(2);
        l.assert_consistent(); let _three = l.push_n(3);
        l.assert_consistent(); assert_eq!(l.len(), 3);
        l.assert_consistent(); l.remove(one);
        l.assert_consistent(); l.remove(two);
        // and through and through, the vorpal blade went snicker-snack
        l.assert_consistent(); assert_eq!(l.len(), 1);
        l.assert_consistent(); assert_eq!(l.head(), 3);
        l.assert_consistent(); assert_eq!(l.tail(), 3);
        l.assert_consistent(); assert_eq!(l.pop().get(), 3);
        l.assert_consistent(); assert!(l.is_empty());
    }
    #[test]
    fn test_dlist_remove_one_three() {
        let l = DList::<int>();
        l.assert_consistent(); let one = l.push_n(1);
        l.assert_consistent(); let _two = l.push_n(2);
        l.assert_consistent(); let three = l.push_n(3);
        l.assert_consistent(); assert_eq!(l.len(), 3);
        l.assert_consistent(); l.remove(one);
        l.assert_consistent(); l.remove(three);
        l.assert_consistent(); assert_eq!(l.len(), 1);
        l.assert_consistent(); assert_eq!(l.head(), 2);
        l.assert_consistent(); assert_eq!(l.tail(), 2);
        l.assert_consistent(); assert_eq!(l.pop().get(), 2);
        l.assert_consistent(); assert!(l.is_empty());
    }
    #[test]
    fn test_dlist_remove_two_three() {
        let l = DList::<int>();
        l.assert_consistent(); let _one = l.push_n(1);
        l.assert_consistent(); let two = l.push_n(2);
        l.assert_consistent(); let three = l.push_n(3);
        l.assert_consistent(); assert_eq!(l.len(), 3);
        l.assert_consistent(); l.remove(two);
        l.assert_consistent(); l.remove(three);
        l.assert_consistent(); assert_eq!(l.len(), 1);
        l.assert_consistent(); assert_eq!(l.head(), 1);
        l.assert_consistent(); assert_eq!(l.tail(), 1);
        l.assert_consistent(); assert_eq!(l.pop().get(), 1);
        l.assert_consistent(); assert!(l.is_empty());
    }
    #[test]
    fn test_dlist_remove_all() {
        let l = DList::<int>();
        l.assert_consistent(); let one = l.push_n(1);
        l.assert_consistent(); let two = l.push_n(2);
        l.assert_consistent(); let three = l.push_n(3);
        l.assert_consistent(); assert_eq!(l.len(), 3);
        l.assert_consistent(); l.remove(two);
        l.assert_consistent(); l.remove(three);
        l.assert_consistent(); l.remove(one); // Twenty-three is number one!
        l.assert_consistent(); assert!(l.peek().is_none());
        l.assert_consistent(); assert!(l.is_empty());
    }
    #[test]
    fn test_dlist_insert_n_before() {
        let l = DList::<int>();
        l.assert_consistent(); let _one = l.push_n(1);
        l.assert_consistent(); let two = l.push_n(2);
        l.assert_consistent(); let three = new_dlist_node(3);
        l.assert_consistent(); assert_eq!(l.len(), 2);
        l.assert_consistent(); l.insert_n_before(three, two);
        l.assert_consistent(); assert_eq!(l.len(), 3);
        l.assert_consistent(); assert_eq!(l.head(), 1);
        l.assert_consistent(); assert_eq!(l.tail(), 2);
        l.assert_consistent(); assert_eq!(l.pop().get(), 1);
        l.assert_consistent(); assert_eq!(l.pop().get(), 3);
        l.assert_consistent(); assert_eq!(l.pop().get(), 2);
        l.assert_consistent(); assert!(l.is_empty());
    }
    #[test]
    fn test_dlist_insert_n_after() {
        let l = DList::<int>();
        l.assert_consistent(); let one = l.push_n(1);
        l.assert_consistent(); let _two = l.push_n(2);
        l.assert_consistent(); let three = new_dlist_node(3);
        l.assert_consistent(); assert_eq!(l.len(), 2);
        l.assert_consistent(); l.insert_n_after(three, one);
        l.assert_consistent(); assert_eq!(l.len(), 3);
        l.assert_consistent(); assert_eq!(l.head(), 1);
        l.assert_consistent(); assert_eq!(l.tail(), 2);
        l.assert_consistent(); assert_eq!(l.pop().get(), 1);
        l.assert_consistent(); assert_eq!(l.pop().get(), 3);
        l.assert_consistent(); assert_eq!(l.pop().get(), 2);
        l.assert_consistent(); assert!(l.is_empty());
    }
    #[test]
    fn test_dlist_insert_before_head() {
        let l = DList::<int>();
        l.assert_consistent(); let one = l.push_n(1);
        l.assert_consistent(); let _two = l.push_n(2);
        l.assert_consistent(); assert_eq!(l.len(), 2);
        l.assert_consistent(); l.insert_before(3, one);
        l.assert_consistent(); assert_eq!(l.len(), 3);
        l.assert_consistent(); assert_eq!(l.head(), 3);
        l.assert_consistent(); assert_eq!(l.tail(), 2);
        l.assert_consistent(); assert_eq!(l.pop().get(), 3);
        l.assert_consistent(); assert_eq!(l.pop().get(), 1);
        l.assert_consistent(); assert_eq!(l.pop().get(), 2);
        l.assert_consistent(); assert!(l.is_empty());
    }
    #[test]
    fn test_dlist_insert_after_tail() {
        let l = DList::<int>();
        l.assert_consistent(); let _one = l.push_n(1);
        l.assert_consistent(); let two = l.push_n(2);
        l.assert_consistent(); assert_eq!(l.len(), 2);
        l.assert_consistent(); l.insert_after(3, two);
        l.assert_consistent(); assert_eq!(l.len(), 3);
        l.assert_consistent(); assert_eq!(l.head(), 1);
        l.assert_consistent(); assert_eq!(l.tail(), 3);
        l.assert_consistent(); assert_eq!(l.pop().get(), 1);
        l.assert_consistent(); assert_eq!(l.pop().get(), 2);
        l.assert_consistent(); assert_eq!(l.pop().get(), 3);
        l.assert_consistent(); assert!(l.is_empty());
    }
    #[test] #[should_fail] #[ignore(cfg(windows))]
    fn test_dlist_asymmetric_link() {
        let l = DList::<int>();
        let _one = l.push_n(1);
        let two = l.push_n(2);
        two.prev = None;
        l.assert_consistent();
    }
    #[test] #[should_fail] #[ignore(cfg(windows))]
    fn test_dlist_cyclic_list() {
        let l = DList::<int>();
        let one = l.push_n(1);
        let _two = l.push_n(2);
        let three = l.push_n(3);
        three.next = Some(one);
        one.prev = Some(three);
        l.assert_consistent();
    }
    #[test] #[should_fail] #[ignore(cfg(windows))]
    fn test_dlist_headless() {
        DList::<int>().head();
    }
    #[test] #[should_fail] #[ignore(cfg(windows))]
    fn test_dlist_insert_already_present_before() {
        let l = DList::<int>();
        let one = l.push_n(1);
        let two = l.push_n(2);
        l.insert_n_before(two, one);
    }
    #[test] #[should_fail] #[ignore(cfg(windows))]
    fn test_dlist_insert_already_present_after() {
        let l = DList::<int>();
        let one = l.push_n(1);
        let two = l.push_n(2);
        l.insert_n_after(one, two);
    }
    #[test] #[should_fail] #[ignore(cfg(windows))]
    fn test_dlist_insert_before_orphan() {
        let l = DList::<int>();
        let one = new_dlist_node(1);
        let two = new_dlist_node(2);
        l.insert_n_before(one, two);
    }
    #[test] #[should_fail] #[ignore(cfg(windows))]
    fn test_dlist_insert_after_orphan() {
        let l = DList::<int>();
        let one = new_dlist_node(1);
        let two = new_dlist_node(2);
        l.insert_n_after(two, one);
    }
}