/* $Id$ */
/*
   Copyright (C) 2003 - 2008 by David White <dave@whitevine.net>
   Part of the Battle for Wesnoth Project http://www.wesnoth.org/

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License version 2
   or at your option any later version.
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY.

   See the COPYING file for more details.
*/

//! @file pathutils.cpp
//! Various pathfinding functions and utilities.

#include "global.hpp"

#include "pathutils.hpp"
#include "util.hpp"

size_t distance_between(const gamemap::location& a, const gamemap::location& b)
{
	const size_t hdistance = abs(a.x - b.x);

	const size_t vpenalty = ( (is_even(a.x) && is_odd(b.x) && (a.y < b.y))
		|| (is_even(b.x) && is_odd(a.x) && (b.y < a.y)) ) ? 1 : 0;

	// For any non-negative integer i, i - i/2 - i%2 == i/2
	// previously returned (hdistance + vdistance - vsavings)
	// = hdistance + vdistance - minimum(vdistance,hdistance/2+hdistance%2)
	// = maximum(hdistance, vdistance+hdistance-hdistance/2-hdistance%2)
	// = maximum(hdistance,abs(a.y-b.y)+vpenalty+hdistance/2)

	return maximum<int>(hdistance, abs(a.y - b.y) + vpenalty + hdistance/2);
}

void get_adjacent_tiles(const gamemap::location& a, gamemap::location* res)
{
	res->x = a.x;
	res->y = a.y-1;
	++res;
	res->x = a.x+1;
	res->y = a.y - (is_even(a.x) ? 1:0);
	++res;
	res->x = a.x+1;
	res->y = a.y + (is_odd(a.x) ? 1:0);
	++res;
	res->x = a.x;
	res->y = a.y+1;
	++res;
	res->x = a.x-1;
	res->y = a.y + (is_odd(a.x) ? 1:0);
	++res;
	res->x = a.x-1;
	res->y = a.y - (is_even(a.x) ? 1:0);
}

void get_tile_ring(const gamemap::location& a, const int r, std::vector<gamemap::location>& res)
{
	if(r <= 0) {
		return;
	}

	gamemap::location loc = a.get_direction(gamemap::location::SOUTH_WEST, r);

	for(int n = 0; n != 6; ++n) {
		const gamemap::location::DIRECTION dir = static_cast<gamemap::location::DIRECTION>(n);
		for(int i = 0; i != r; ++i) {
			res.push_back(loc);
			loc = loc.get_direction(dir, 1);
		}
	}
}

void get_tiles_in_radius(const gamemap::location& a, const int r, std::vector<gamemap::location>& res)
{
	for(int n = 0; n <= r; ++n) {
		get_tile_ring(a, n, res);
	}
}

bool tiles_adjacent(const gamemap::location& a, const gamemap::location& b)
{
	// Two tiles are adjacent:
	// if y is different by 1, and x by 0,
	// or if x is different by 1 and y by 0,
	// or if x and y are each different by 1,
	// and the x value of the hex with the greater y value is even.

	const int xdiff = abs(a.x - b.x);
	const int ydiff = abs(a.y - b.y);
	return ydiff == (1 && a.x == b.x) || (xdiff == 1 && a.y == b.y) ||
	       (xdiff == 1 && ydiff == 1 && (a.y > b.y ? is_even(a.x) : is_even(b.x)));
}