/*

Idea: provide functions for 'exhaustive' and 'random' modification of vecs.

  two functions, "return all edits" and "return a random edit" <--
    leaning toward this model or two functions, "return the number of
    possible edits" and "return edit #n"

It would be nice if this could be data-driven, so the two functions
could share information:
  type vec_modifier = rec(fn (<T> v, uint i) -> ~[T] fun, uint lo, uint di);
  const ~[vec_modifier] vec_modifiers = ~[rec(fun=vec_omit, 0u, 1u), ...]/~;
But that gives me "error: internal compiler error unimplemented consts
that's not a plain literal".
https://github.com/graydon/rust/issues/570

vec_edits is not an iter because iters might go away.

*/

use std;
import vec;
import vec::slice;
import vec::len;
import int;

fn vec_omit<T: copy>(v: ~[T], i: uint) -> ~[T] {
    slice(v, 0u, i) + slice(v, i + 1u, len(v))
}
fn vec_dup<T: copy>(v: ~[T], i: uint) -> ~[T] {
    slice(v, 0u, i) + [v[i]] + slice(v, i, len(v))
}
fn vec_swadj<T: copy>(v: ~[T], i: uint) -> ~[T] {
    slice(v, 0u, i) + [v[i + 1u], v[i]] + slice(v, i + 2u, len(v))
}
fn vec_prefix<T: copy>(v: ~[T], i: uint) -> ~[T] { slice(v, 0u, i) }
fn vec_suffix<T: copy>(v: ~[T], i: uint) -> ~[T] { slice(v, i, len(v)) }

fn vec_poke<T: copy>(v: ~[T], i: uint, x: T) -> ~[T] {
    slice(v, 0u, i) + ~[x] + slice(v, i + 1u, len(v))
}
fn vec_insert<T: copy>(v: ~[T], i: uint, x: T) -> ~[T] {
    slice(v, 0u, i) + ~[x] + slice(v, i, len(v))
}

// Iterates over 0...length, skipping the specified number on each side.
fn ix(skip_low: uint, skip_high: uint, length: uint, it: block(uint)) {
    let i: uint = skip_low;
    while i + skip_high <= length { it(i); i += 1u; }
}

// Returns a bunch of modified versions of v, some of which introduce
// new elements (borrowed from xs).
fn vec_edits<T: copy>(v: ~[T], xs: ~[T]) -> ~[~[T]] {
    let edits: ~[~[T]] = ~[];
    let Lv: uint = len(v);

    if Lv != 1u {
        // When Lv == 1u, this is redundant with omit.
        vec::push(edits, ~[]);
    }
    if Lv >= 3u {
        // When Lv == 2u, this is redundant with swap.
        vec::push(edits, vec::reversed(v));
    }
    ix(0u, 1u, Lv) {|i| edits += ~[vec_omit(v, i)]; }
    ix(0u, 1u, Lv) {|i| edits += ~[vec_dup(v, i)]; }
    ix(0u, 2u, Lv) {|i| edits += ~[vec_swadj(v, i)]; }
    ix(1u, 2u, Lv) {|i| edits += ~[vec_prefix(v, i)]; }
    ix(2u, 1u, Lv) {|i| edits += ~[vec_suffix(v, i)]; }

    ix(0u, 1u, len(xs)) {|j|
        ix(0u, 1u, Lv) {|i|
            vec::push(edits, vec_poke(v, i, xs[j]));
        }
        ix(0u, 0u, Lv) {|i|
            vec::push(edits, vec_insert(v, i, xs[j]));
        }
    }

    edits
}

// Would be nice if this were built in:
// https://github.com/graydon/rust/issues/424
fn vec_to_str(v: ~[int]) -> str {
    let i = 0u;
    let s = "[";
    while i < len(v) {
        s += int::str(v[i]);
        if i + 1u < len(v) { s += ", "; }
        i += 1u;
    }
    ret s + "]";
}

fn show_edits(a: ~[int], xs: ~[int]) {
    log(error, "=== Edits of " + vec_to_str(a) + " ===");
    let b = vec_edits(a, xs);
    ix(0u, 1u, len(b)) {|i| log(error, vec_to_str(b[i])); }
}

fn demo_edits() {
    let xs = ~[7, 8];
    show_edits(~[], xs);
    show_edits(~[1], xs);
    show_edits(~[1, 2], xs);
    show_edits(~[1, 2, 3], xs);
    show_edits(~[1, 2, 3, 4], xs);
}

fn main() { demo_edits(); }
