use game::{Position, Move, ZobristHash, NumPlies};

use negamax::Bound;

#[derive(Clone, Debug)]
pub struct Data {
    pub hash: ZobristHash,
    pub depth: NumPlies,
    pub bound: Bound,
    pub best_move_opt: Option<Move>,
}

pub struct TranspositionTable(Vec<Option<Data>>);
impl TranspositionTable {
    pub fn with_capacity(capacity: usize) -> Self {
        TranspositionTable(vec![None; capacity])
    }
    pub fn get<'a>(&'a self, pos: &Position) -> Option<&'a Data> {
        let hash = pos.hash();
        let idx = (hash.0 % (self.0.len() as u64)) as usize;
        self.0[idx].as_ref().and_then(|x| {
            let is_correct_pos = x.hash == hash &&
                                 x.best_move_opt.as_ref()
                                  .map_or(true, |y| pos.legal_iter().any(|z| *y == z));
            if is_correct_pos { Some(x) } else { None }
        })
    }
    // TODO implement a better replacement scheme
    pub fn set(&mut self, pos: &Position, depth: NumPlies, best_move_opt: Option<Move>, bound: Bound) {
        let hash = pos.hash();
        let idx = (hash.0 % (self.0.len() as u64)) as usize;
        self.0[idx] = Some(Data { hash: hash, depth: depth, best_move_opt: best_move_opt, bound: bound });
    }
}

use game::{Position, Move, ZobristHash, NumPlies};

use negamax::Bound;

#[derive(Clone, Debug)]
pub struct Data {
    pub hash: ZobristHash,
    pub depth: NumPlies,
    pub bound: Bound,
    pub best_move_opt: Option<Move>,
}

pub struct TranspositionTable(Vec<Option<Data>>);
impl TranspositionTable {
    pub fn with_capacity(capacity: usize) -> Self {
        TranspositionTable(vec![None; capacity])
    }
    pub fn get<'a>(&'a self, pos: &Position) -> Option<&'a Data> {
        let hash = pos.hash();
        let idx = (hash.0 % (self.0.len() as u64)) as usize;
        self.0[idx].as_ref().and_then(|x| if x.hash == hash { Some(x) } else { None })
    }
    // TODO implement a better replacement scheme
    pub fn set(&mut self, pos: &Position, depth: NumPlies, best_move_opt: Option<Move>, bound: Bound) {
        let hash = pos.hash();
        let idx = (hash.0 % (self.0.len() as u64)) as usize;
        self.0[idx] = Some(Data { hash: hash, depth: depth, best_move_opt: best_move_opt, bound: bound });
    }
}

--- 
+++ 
@@ -18,7 +18,12 @@
     pub fn get<'a>(&'a self, pos: &Position) -> Option<&'a Data> {
         let hash = pos.hash();
         let idx = (hash.0 % (self.0.len() as u64)) as usize;
-        self.0[idx].as_ref().and_then(|x| if x.hash == hash { Some(x) } else { None })
+        self.0[idx].as_ref().and_then(|x| {
+            let is_correct_pos = x.hash == hash &&
+                                 x.best_move_opt.as_ref()
+                                  .map_or(true, |y| pos.legal_iter().any(|z| *y == z));
+            if is_correct_pos { Some(x) } else { None }
+        })
     }
     // TODO implement a better replacement scheme
     pub fn set(&mut self, pos: &Position, depth: NumPlies, best_move_opt: Option<Move>, bound: Bound) {
Check if best move in transposition table is valid
