/*

     File: WormGuts.c

 Abstract: C-based game engine.

  Version: 1.2

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 */

#include "WormGuts.h"

#include <stdlib.h>

GameState worm_guts(GamePosition *wormPositions, unsigned long *wormLength, GameDirection *wormDirection, GameHeading *wormHeading, GamePosition *targetPosition, unsigned long width, unsigned long height, long noBounce) {

    int retval = kGameStateContinue;

    unsigned long i;

    if (wormPositions[0].x == targetPosition->x && wormPositions[0].y == targetPosition->y) {   /* Check target */

        unsigned collisions;

        if (targetPosition->x >= 0 && targetPosition->y >= 0) retval = kGameStateScore;     /* Account for initial state */

        do {    /* Compute new location for target */

            targetPosition->x = random() % width;

            targetPosition->y = random() % height;

            for (i = 0, collisions = 0; collisions == 0 && i < *wormLength; i++) {

                if (targetPosition->x == wormPositions[i].x && targetPosition->y == wormPositions[i].y) collisions++;

            }

        } while (collisions > 0);

        (*wormLength)++;

    }

    for (i = *wormLength; i > 0; i--) { /* Advance worm */

        wormPositions[i] = wormPositions[i-1];

    }

    *wormDirection = (*wormDirection + *wormHeading) % 4;

    wormPositions[0].x += (*wormDirection == kGameDirectionEast) - (*wormDirection == kGameDirectionWest);

    wormPositions[0].y += (*wormDirection == kGameDirectionSouth) - (*wormDirection == kGameDirectionNorth);

    if (*wormHeading != kGameHeadingStraight && (wormPositions[0].x < 0 || wormPositions[0].x >= width || wormPositions[0].y < 0 || wormPositions[0].y >= height)) {

        wormPositions[0].x -= (*wormDirection == kGameDirectionEast) - (*wormDirection == kGameDirectionWest);

        wormPositions[0].y -= (*wormDirection == kGameDirectionSouth) - (*wormDirection == kGameDirectionNorth);

        *wormDirection = (*wormDirection - *wormHeading) % 4;

        wormPositions[0].x += (*wormDirection == kGameDirectionEast) - (*wormDirection == kGameDirectionWest);

        wormPositions[0].y += (*wormDirection == kGameDirectionSouth) - (*wormDirection == kGameDirectionNorth);

    }

    *wormHeading = kGameHeadingStraight;

    if (wormPositions[0].x < 0 || wormPositions[0].x >= width) {    /* Hit the wall; turn or end game */

        if (noBounce) { /* Done */

            retval = kGameStateCrash;   

        } else {    /* Turn */

            wormPositions[0].x = (wormPositions[0].x < 0) ? 0 : width - 1;

            *wormDirection = (wormPositions[0].y < height / 2) ? kGameDirectionSouth : kGameDirectionNorth;

            wormPositions[0].y += (*wormDirection == kGameDirectionSouth) - (*wormDirection == kGameDirectionNorth);

        }

    } else if (wormPositions[0].y < 0 || wormPositions[0].y >= height) {        /* Hit the wall; turn or end game */

        if (noBounce) { /* Done */

            retval = kGameStateCrash;       

        } else {    /* Turn */

            wormPositions[0].y = (wormPositions[0].y < 0) ? 0 : height - 1;

            *wormDirection = (wormPositions[0].x < width / 2) ? kGameDirectionEast : kGameDirectionWest;

            wormPositions[0].x += (*wormDirection == kGameDirectionEast) - (*wormDirection == kGameDirectionWest);

        }

    }

    for (i = 1; retval != kGameStateCrash && i < *wormLength; i++) {

        if (wormPositions[0].x == wormPositions[i].x && wormPositions[0].y == wormPositions[i].y) retval = kGameStateCrash;

    }

    return retval;

}