/* $Id$ */

/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */

/** @file direction_func.h Different functions related to conversions between directions. */

#ifndef DIRECTION_FUNC_H
#define DIRECTION_FUNC_H

#include "direction_type.h"

/**
 * Checks if an integer value is a valid DiagDirection
 *
 * @param d The value to check
 * @return True if the value belongs to a DiagDirection, else false
 */
static inline bool IsValidDiagDirection(DiagDirection d)
{
	return d < DIAGDIR_END;
}

/**
 * Checks if an integer value is a valid Direction
 *
 * @param d The value to check
 * @return True if the value belongs to a Direction, else false
 */
static inline bool IsValidDirection(Direction d)
{
	return d < DIR_END;
}

/**
 * Checks if an integer value is a valid Axis
 *
 * @param d The value to check
 * @return True if the value belongs to an Axis, else false
 */
static inline bool IsValidAxis(Axis d)
{
	return d < AXIS_END;
}

/**
 * Return the reverse of a direction
 *
 * @param d The direction to get the reverse from
 * @return The reverse Direction
 */
static inline Direction ReverseDir(Direction d)
{
	assert(IsValidDirection(d));
	return (Direction)(4 ^ d);
}


/**
 * Calculate the difference between two directions
 *
 * @param d0 The first direction as the base
 * @param d1 The second direction as the offset from the base
 * @return The difference how the second direction drifts of the first one.
 */
static inline DirDiff DirDifference(Direction d0, Direction d1)
{
	assert(IsValidDirection(d0));
	assert(IsValidDirection(d1));
	/* Cast to uint so compiler can use bitmask. If the difference is negative
	 * and we used int instead of uint, further "+ 8" would have to be added. */
	return (DirDiff)((uint)(d0 - d1) % 8);
}

/**
 * Applies two differences together
 *
 * This function adds two differences together and returns the resulting
 * difference. So adding two DIRDIFF_REVERSE together results in the
 * DIRDIFF_SAME difference.
 *
 * @param d The first difference
 * @param delta The second difference to add on
 * @return The resulting difference
 */
static inline DirDiff ChangeDirDiff(DirDiff d, DirDiff delta)
{
	/* Cast to uint so compiler can use bitmask. Result can never be negative. */
	return (DirDiff)((uint)(d + delta) % 8);
}

/**
 * Change a direction by a given difference
 *
 * This functions returns a new direction of the given direction
 * which is rotated by the given difference.
 *
 * @param d The direction to get a new direction from
 * @param delta The offset/drift applied to the direction
 * @return The new direction
 */
static inline Direction ChangeDir(Direction d, DirDiff delta)
{
	assert(IsValidDirection(d));
	/* Cast to uint so compiler can use bitmask. Result can never be negative. */
	return (Direction)((uint)(d + delta) % 8);
}


/**
 * Returns the reverse direction of the given DiagDirection
 *
 * @param d The DiagDirection to get the reverse from
 * @return The reverse direction
 */
static inline DiagDirection ReverseDiagDir(DiagDirection d)
{
	assert(IsValidDiagDirection(d));
	return (DiagDirection)(2 ^ d);
}

/**
 * Calculate the difference between two DiagDirection values
 *
 * @param d0 The first direction as the base
 * @param d1 The second direction as the offset from the base
 * @return The difference how the second direction drifts of the first one.
 */
static inline DiagDirDiff DiagDirDifference(DiagDirection d0, DiagDirection d1)
{
	assert(IsValidDiagDirection(d0));
	assert(IsValidDiagDirection(d1));
	/* Cast to uint so compiler can use bitmask. Result can never be negative. */
	return (DiagDirDiff)((uint)(d0 - d1) % 4);
}

/**
 * Applies a difference on a DiagDirection
 *
 * This function applies a difference on a DiagDirection and returns
 * the new DiagDirection.
 *
 * @param d The DiagDirection
 * @param delta The difference to apply on
 * @return The new direction which was calculated
 */
static inline DiagDirection ChangeDiagDir(DiagDirection d, DiagDirDiff delta)
{
	assert(IsValidDiagDirection(d));
	/* Cast to uint so compiler can use bitmask. Result can never be negative. */
	return (DiagDirection)((uint)(d + delta) % 4);
}

/**
 * Convert a Direction to a DiagDirection.
 *
 * This function can be used to convert the 8-way Direction to
 * the 4-way DiagDirection. If the direction cannot be mapped its
 * "rounded clockwise". So DIR_N becomes DIAGDIR_NE.
 *
 * @param dir The direction to convert
 * @return The resulting DiagDirection, maybe "rounded clockwise".
 */
static inline DiagDirection DirToDiagDir(Direction dir)
{
	assert(IsValidDirection(dir));
	return (DiagDirection)(dir >> 1);
}

/**
 * Convert a DiagDirection to a Direction.
 *
 * This function can be used to convert the 4-way DiagDirection
 * to the 8-way Direction. As 4-way are less than 8-way not all
 * possible directions can be calculated.
 *
 * @param dir The direction to convert
 * @return The resulting Direction
 */
static inline Direction DiagDirToDir(DiagDirection dir)
{
	assert(IsValidDiagDirection(dir));
	return (Direction)(dir * 2 + 1);
}


/**
 * Select the other axis as provided.
 *
 * This is basically the not-operator for the axis.
 *
 * @param a The given axis
 * @return The other axis
 */
static inline Axis OtherAxis(Axis a)
{
	assert(IsValidAxis(a));
	return (Axis)(a ^ 1);
}


/**
 * Convert a DiagDirection to the axis.
 *
 * This function returns the axis which belongs to the given
 * DiagDirection. The axis X belongs to the DiagDirection
 * north-east and south-west.
 *
 * @param d The DiagDirection
 * @return The axis which belongs to the direction
 */
static inline Axis DiagDirToAxis(DiagDirection d)
{
	assert(IsValidDiagDirection(d));
	return (Axis)(d & 1);
}


/**
 * Converts an Axis to a DiagDirection
 *
 * This function returns the DiagDirection which
 * belongs to the axis. As 2 directions are mapped to an axis
 * this function returns the one which points to south,
 * either south-west (on X axis) or south-east (on Y axis)
 *
 * @param a The axis
 * @return The direction pointed to south
 */
static inline DiagDirection AxisToDiagDir(Axis a)
{
	assert(IsValidAxis(a));
	return (DiagDirection)(2 - a);
}

/**
 * Converts an Axis to a Direction
 *
 * This function returns the Direction which
 * belongs to the axis. As 2 directions are mapped to an axis
 * this function returns the one which points to south,
 * either south-west (on X axis) or south-east (on Y axis)
 *
 * @param a The axis
 * @return The direction pointed to south
 */
static inline Direction AxisToDirection(Axis a)
{
	assert(IsValidAxis(a));
	return (Direction)(5 - 2 * a);
}

/**
 * Convert an axis and a flag for north/south into a DiagDirection
 * @param xy axis to convert
 * @param ns north -> 0, south -> 1
 * @return the desired DiagDirection
 */
static inline DiagDirection XYNSToDiagDir(Axis xy, uint ns)
{
	assert(IsValidAxis(xy));
	return (DiagDirection)(xy * 3 ^ ns * 2);
}

/**
 * Checks if a given Direction is diagonal.
 *
 * @param dir The given direction.
 * @return True if the direction is diagonal.
 */
static inline bool IsDiagonalDirection(Direction dir)
{
	assert(IsValidDirection(dir));
	return (dir & 1) != 0;
}

#endif /* DIRECTION_FUNC_H */
