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// IMPORTANT VARIABLE DECLARATIONS:

#define SPATIAL_PARTITION_DYNAMIC 3

typedef struct SurfaceNode SpatialPartitionCell[4];

extern SpatialPartitionCell gStaticSurfacePartition[16][16];
extern SpatialPartitionCell gDynamicSurfacePartition[16][16];
extern struct SurfaceNode *sSurfaceNodePool;
extern struct Surface *sSurfacePool;
extern s16 sSurfacePoolSize;


static void add_surface_to_cell(s16 dynamic, s16 cellX, s16 cellZ, struct Surface *surface) {
    struct SurfaceNode *newNode = alloc_surface_node();
    struct SurfaceNode *newDynNode = alloc_surface_node();

    struct SurfaceNode *list;
    struct SurfaceNode *dynList;

    s16 surfacePriority;
    s16 priority;
    s16 sortDir;
    s16 listIndex;

    s16 floorOrCeiling = 0;

    if (surface->normal.y > 0.01) {
        listIndex = SPATIAL_PARTITION_FLOORS;
        sortDir = 1; // highest to lowest, then insertion order
        floorOrCeiling = 1;
    } else if (surface->normal.y < -0.01) {
        listIndex = SPATIAL_PARTITION_CEILS;
        sortDir = -1; // lowest to highest, then insertion order
        floorOrCeiling = 1;
    } else {
        listIndex = SPATIAL_PARTITION_WALLS;
        sortDir = 0; // insertion order

        if (surface->normal.x < -0.707 || surface->normal.x > 0.707) {
            surface->flags |= SURFACE_FLAG_X_PROJECTION;
        }
    }

    //! (Surface Cucking) Surfaces are sorted by the height of their first
    //  vertex. Since vertices aren't ordered by height, this causes many
    //  lower triangles to be sorted higher. This worsens surface cucking since
    //  many functions only use the first triangle in surface order that fits,
    //  missing higher surfaces.
    //  upperY would be a better sort method.
    surfacePriority = surface->vertex1[1] * sortDir;

    newNode->surface = surface;

    newDynNode->surface = surface;


    if (dynamic) {
        list = &gDynamicSurfacePartition[cellZ][cellX][listIndex];
        if (floorOrCeiling)
            dynList = &gDynamicSurfacePartition[cellZ][cellX][SPATIAL_PARTITION_DYNAMIC];
    } else {
        list = &gStaticSurfacePartition[cellZ][cellX][listIndex];
        if (floorOrCeiling)
            dynList = &gStaticSurfacePartition[cellZ][cellX][SPATIAL_PARTITION_DYNAMIC];
    }

    // Loop until we find the appropriate place for the surface in the list.
    while (list->next != NULL) {
        priority = list->next->surface->vertex1[1] * sortDir;

        if (surfacePriority > priority) {
            break;
        }

        list = list->next;
    }
    while (dynList->next != NULL) {
        priority = dynList->next->surface->vertex1[1] * sortDir;

        if (surfacePriority > priority) {
            break;
        }

        dynList = dynList->next;
    }

    newNode->next = list->next;
    list->next = newNode;

    newDynNode->next = dynList->next;
    dynList->next = newDynNode;
}