/*
Module: deque

A deque.  Untested as of yet.  Likely buggy.
*/

/*
Object: t
*/
type t<T> = obj {
    // Method: size
    fn size() -> uint;
    // Method: add_front
    fn add_front(T);
    // Method: add_back
    fn add_back(T);
    // Method: pop_front
    fn pop_front() -> T;
    // Method: pop_back
    fn pop_back() -> T;
    // Method: peek_front
    fn peek_front() -> T;
    // Method: peek_back
    fn peek_back() -> T;
    // Method: get
    fn get(int) -> T;
    };

/*
Section: Functions
*/

/*
Function: create
*/
fn create<copy T>() -> t<T> {
    type cell<T> = option::t<T>;

    let initial_capacity: uint = 32u; // 2^5
     /**
      * Grow is only called on full elts, so nelts is also len(elts), unlike
      * elsewhere.
      */
    fn grow<copy T>(nelts: uint, lo: uint, elts: [mutable cell<T>]) ->
       [mutable cell<T>] {
        assert (nelts == vec::len(elts));
        let rv = [mutable];

        let i = 0u;
        let nalloc = uint::next_power_of_two(nelts + 1u);
        while i < nalloc {
            if i < nelts {
                rv += [mutable elts[(lo + i) % nelts]];
            } else { rv += [mutable option::none]; }
            i += 1u;
        }

        ret rv;
    }
    fn get<T>(elts: [mutable cell<T>], i: uint) -> T {
        ret alt elts[i] { option::some(t) { t } _ { fail } };
    }
    obj deque<copy T>(mutable nelts: uint,
                      mutable lo: uint,
                      mutable hi: uint,
                      mutable elts: [mutable cell<T>]) {
        fn size() -> uint { ret nelts; }
        fn add_front(t: T) {
            let oldlo: uint = lo;
            if lo == 0u {
                lo = vec::len::<cell<T>>(elts) - 1u;
            } else { lo -= 1u; }
            if lo == hi {
                elts = grow::<T>(nelts, oldlo, elts);
                lo = vec::len::<cell<T>>(elts) - 1u;
                hi = nelts;
            }
            elts[lo] = option::some::<T>(t);
            nelts += 1u;
        }
        fn add_back(t: T) {
            if lo == hi && nelts != 0u {
                elts = grow::<T>(nelts, lo, elts);
                lo = 0u;
                hi = nelts;
            }
            elts[hi] = option::some::<T>(t);
            hi = (hi + 1u) % vec::len::<cell<T>>(elts);
            nelts += 1u;
        }

        /**
         * We actually release (turn to none()) the T we're popping so
         * that we don't keep anyone's refcount up unexpectedly.
         */
        fn pop_front() -> T {
            let t: T = get::<T>(elts, lo);
            elts[lo] = option::none::<T>;
            lo = (lo + 1u) % vec::len::<cell<T>>(elts);
            nelts -= 1u;
            ret t;
        }
        fn pop_back() -> T {
            if hi == 0u {
                hi = vec::len::<cell<T>>(elts) - 1u;
            } else { hi -= 1u; }
            let t: T = get::<T>(elts, hi);
            elts[hi] = option::none::<T>;
            nelts -= 1u;
            ret t;
        }
        fn peek_front() -> T { ret get::<T>(elts, lo); }
        fn peek_back() -> T { ret get::<T>(elts, hi - 1u); }
        fn get(i: int) -> T {
            let idx: uint = (lo + (i as uint)) % vec::len::<cell<T>>(elts);
            ret get::<T>(elts, idx);
        }
    }
    let v: [mutable cell<T>] =
        vec::init_elt_mut(option::none, initial_capacity);
    ret deque::<T>(0u, 0u, 0u, v);
}
// Local Variables:
// mode: rust;
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// End: