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extern crate time;

use {Player, MoveResult};
use game_manager::{Game, State};
use gdl::{Move, Score, Role};

use std::cmp::{max, min};

/// An alpha beta search player with a bounded depth. This player should only be used for 2 player
/// games.
pub struct AlphaBetaPlayer {
    depth_limit: u32,
    best_move: Option<Move>
}

impl AlphaBetaPlayer {
    /// Returns a AlphaBetaPlayer that does not recurse past the given depth
    pub fn new(depth: u32) -> AlphaBetaPlayer {
        AlphaBetaPlayer { depth_limit: depth, best_move: None }
    }

    fn best_move(&mut self, game: &Game) -> MoveResult<Move> {
        let role = game.role();
        let cur_state = game.current_state();
        let mut moves = game.legal_moves(cur_state, role);
        assert!(moves.len() >= 1, "No legal moves");

        if moves.len() == 1 {
            return Ok(moves.swap_remove(0));
        }

        let mut max = 0;
        let mut res = moves[0].clone();
        self.best_move = Some(res.clone());
        let opponent = opponent(game, role);
        for m in moves {
            let score = match self.min_score(game, cur_state, &opponent, m.clone(), 0, 100, 0) {
                Ok(score) => score,
                Err(m) => return Err(m)
            };
            if score == 100 {
                return Ok(m);
            } else if score > max {
                max = score;
                self.best_move = Some(m.clone());
                res = m
            }
            check_time_result!(self, game);
        }
        Ok(res)
    }

    fn max_score(&mut self, game: &Game, state: &State, role: &Role, alpha: u8, beta: u8,
                 depth: u32) -> MoveResult<Score> {
        if depth >= self.depth_limit {
            return Ok(game.goal(state, game.role()));
        }

        if game.is_terminal(state) {
            return Ok(game.goal(state, game.role()));
        }

        let moves = game.legal_moves(state, role);
        assert!(!moves.is_empty(), "No legal moves");

        let opponent = opponent(game, role);
        let mut alpha = alpha;
        for m in moves {
            let res = match self.min_score(game, state, &opponent, m, alpha, beta, depth + 1) {
                Ok(score) => score,
                e @ Err(_) => return e
            };

            alpha = max(res, alpha);
            if alpha >= beta {
                return Ok(beta);
            }
            check_time_result!(self, game);
        }
        Ok(alpha)
    }

    fn min_score(&mut self, game: &Game, state: &State, role: &Role, last_move: Move, alpha: u8,
                 beta: u8, depth: u32) -> MoveResult<Score> {
        let moves = game.legal_moves(state, role);
        assert!(!moves.is_empty(), "No legal moves");

        let mut beta = beta;
        for m in moves {
            let move_vec = if game.roles()[0] == *role {
                vec![m, last_move.clone()]
            } else {
                vec![last_move.clone(), m]
            };
            let s = game.next_state(state, &*move_vec);
            let opponent = opponent(game, role);
            let res = match self.max_score(game, &s, &opponent, alpha, beta, depth) {
                Ok(score) => score,
                e @ Err(_) => return e
            };
            beta = min(res, beta);
            if beta <= alpha {
                return Ok(alpha);
            }
            check_time_result!(self, game);
        }
        Ok(beta)
    }

}

impl Player for AlphaBetaPlayer {
    fn name(&self) -> String {
        "AlphaBetaPlayer".to_string()
    }

    fn select_move(&mut self, game: &Game) -> Move {
        let m = match self.best_move(&game) {
            Ok(m) => m,
            Err(m) => { warn!("Out of time"); m }
        };
        info!("Selecting move {}", m.to_string());
        m
    }

    fn out_of_time(&mut self, _: &Game) -> Move {
        self.best_move.take().unwrap()
    }
}

fn opponent<'a>(game: &'a Game, role: &'a Role) -> &'a Role {
    let roles = game.roles();
    assert!(roles.len() == 2, "Must be a two player game");
    let res: Vec<_> = roles.into_iter().filter(|r| *r != role).collect();
    assert_eq!(res.len(), 1);
    res[0]
}