/*
A key,value store that works on anything.

This works using a binary search tree. In the first version, it's a
very naive algorithm, but it will probably be updated to be a
red-black tree or something else.

*/

import option::some;
import option::none;
import option = option::t;

export treemap;
export init;
export insert;
export find;
export traverse;

tag tree_node<@K, @V> {
    empty;
    node(@K, @V, treemap<K, V>, treemap<K, V>);
}

type treemap<@K, @V> = @mutable tree_node<K, V>;

fn init<@K, @V>() -> treemap<K,V> { @mutable empty }

fn insert<@K, @V>(m : &treemap<K, V>, k : &K, v : &V) {
    alt m {
      @empty. {
        *m = node(@k, @v, @mutable empty, @mutable empty);
      }
      @node(@kk, _, _, _) {
        // We have to name left and right individually, because
        // otherwise the alias checker complains.
        if k < kk {
            alt m {
              @node(_, _, left, _) {
                insert(left, k, v);
              }
            }
        }
        else {
            alt m {
              @node(_, _, _, right) {
                insert(right, k, v);
              }
            }
        }
      }
    }
}

fn find<@K, @V>(m : &treemap<K, V>, k : &K) -> option<V> {
  alt *m {
    empty. { none }
    node(@kk, @v, _, _) {
      if k == kk { some(v) }
      // Again, ugliness to unpack left and right individually.
      else if k < kk {
          alt *m {
            node(_, _, left, _) {
              find(left, k)
            }
          }
      }
      else {
          alt *m {
            node(_, _, _, right) {
              find(right, k)
            }
          }
      }
    }
  }
}

// Performs an in-order traversal
fn traverse<@K, @V>(m : &treemap<K, V>, f : fn(&K, &V)) {
  alt *m {
    empty. { }
    node(@k, @v, _, _) {
      // copy v to make aliases work out
      let v1 = v;
      alt *m {
        node(_, _, left, _) {
          traverse(left, f);
        }
      }
      f(k, v1);
      alt *m {
        node(_, _, _, right) {
          traverse(right, f);
        }
      }
    }
  }
}