import vec::len;
import vec::slice;

export merge_sort;
export quick_sort;
export quick_sort3;

type lteq<T> = block(&T, &T) -> bool ;

fn merge_sort<@T>(le: &lteq<T>, v: &[T]) -> [T] {
    fn merge<@T>(le: &lteq<T>, a: &[T], b: &[T]) -> [T] {
        let rs: [T] = ~[];
        let a_len: uint = len[T](a);
        let a_ix: uint = 0u;
        let b_len: uint = len[T](b);
        let b_ix: uint = 0u;
        while a_ix < a_len && b_ix < b_len {
            if le(a.(a_ix), b.(b_ix)) {
                rs += ~[a.(a_ix)];
                a_ix += 1u;
            } else { rs += ~[b.(b_ix)]; b_ix += 1u; }
        }
        rs += slice[T](a, a_ix, a_len);
        rs += slice[T](b, b_ix, b_len);
        ret rs;
    }
    let v_len: uint = len[T](v);
    if v_len <= 1u { ret v; }
    let mid: uint = v_len / 2u;
    let a: [T] = slice[T](v, 0u, mid);
    let b: [T] = slice[T](v, mid, v_len);
    ret merge[T](le, merge_sort[T](le, a), merge_sort[T](le, b));
}

fn swap<@T>(arr: &[mutable T], x: uint, y: uint) {
    let a = arr.(x);
    arr.(x) = arr.(y);
    arr.(y) = a;
}

fn part<@T>(compare_func: &lteq<T>, arr: &[mutable T], left: uint,
            right: uint, pivot: uint) -> uint {
    let pivot_value = arr.(pivot);
    swap[T](arr, pivot, right);
    let storage_index: uint = left;
    let i: uint = left;
    while i < right {
        if compare_func({ arr.(i) }, pivot_value) {
            swap[T](arr, i, storage_index);
            storage_index += 1u;
        }
        i += 1u;
    }
    swap[T](arr, storage_index, right);
    ret storage_index;
}

fn qsort<@T>(compare_func: &lteq<T>, arr: &[mutable T], left: uint,
             right: uint) {
    if right > left {
        let pivot = (left + right) / 2u;
        let new_pivot = part[T](compare_func, arr, left, right, pivot);
        if new_pivot != 0u {
            // Need to do this check before recursing due to overflow
            qsort[T](compare_func, arr, left, new_pivot - 1u);
        }
        qsort[T](compare_func, arr, new_pivot + 1u, right);
    }
}

fn quick_sort<@T>(compare_func: &lteq<T>, arr: &[mutable T]) {
    if len[T](arr) == 0u { ret; }
    qsort[T](compare_func, arr, 0u, len[T](arr) - 1u);
}


// Based on algorithm presented by Sedgewick and Bentley here:
// http://www.cs.princeton.edu/~rs/talks/QuicksortIsOptimal.pdf
// According to these slides this is the algorithm of choice for
// 'randomly ordered keys, abstract compare' & 'small number of key values'
fn qsort3<@T>(compare_func_lt: &lteq<T>, compare_func_eq: &lteq<T>,
              arr: &[mutable T], left: int, right: int) {
    if right <= left { ret; }
    let v: T = arr.(right);
    let i: int = left - 1;
    let j: int = right;
    let p: int = i;
    let q: int = j;
    while true {
        i += 1;
        while compare_func_lt({ arr.(i) }, v) { i += 1; }
        j -= 1;
        while compare_func_lt(v, { arr.(j) }) {
            if j == left { break; }
            j -= 1;
        }
        if i >= j { break; }
        swap[T](arr, i as uint, j as uint);
        if compare_func_eq({ arr.(i) }, v) {
            p += 1;
            swap[T](arr, p as uint, i as uint);
        }
        if compare_func_eq(v, { arr.(j) }) {
            q -= 1;
            swap[T](arr, j as uint, q as uint);
        }
    }
    swap[T](arr, i as uint, right as uint);
    j = i - 1;
    i += 1;
    let k: int = left;
    while k < p {
        swap[T](arr, k as uint, j as uint);
        k += 1;
        j -= 1;
        if k == len[T](arr) as int { break; }
    }
    k = right - 1;
    while k > q {
        swap[T](arr, i as uint, k as uint);
        k -= 1;
        i += 1;
        if k == 0 { break; }
    }
    qsort3[T](compare_func_lt, compare_func_eq, arr, left, j);
    qsort3[T](compare_func_lt, compare_func_eq, arr, i, right);
}

fn quick_sort3<@T>(compare_func_lt: &lteq<T>, compare_func_eq: &lteq<T>,
                   arr: &[mutable T]) {
    if len[T](arr) == 0u { ret; }
    qsort3[T](compare_func_lt, compare_func_eq, arr, 0,
              (len[T](arr) as int) - 1);
}

// Local Variables:
// mode: rust;
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// compile-command: "make -k -C $RBUILD 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
// End: