feely_pona/feely_pona_game.cpp

#if defined(_CLANGD)
    #pragma once
    #include "feely_pona_unity.h"
#endif

static bool FP_Game_KeyBindIsPressed(TELY_OSInput const *input, FP_GameControls const *controls, FP_GameKeyBind key_bind)
{
    bool result = false;
    if (controls->mode == FP_GameControlMode_Keyboard) {
        result = TELY_OSInput_ScanKeyIsPressed(input, key_bind.scan_key);
    } else {
        result = TELY_OSInput_GamepadKeyIsPressed(input, controls->gamepad_index, key_bind.gamepad_key);
    }
    return result;
}

static bool FP_Game_KeyBindIsDown(TELY_OSInput const *input, FP_GameControls const *controls, FP_GameKeyBind key_bind)
{
    bool result = false;
    if (controls->mode == FP_GameControlMode_Keyboard) {
        result = TELY_OSInput_ScanKeyIsDown(input, key_bind.scan_key);
    } else {
        result = TELY_OSInput_GamepadKeyIsDown(input, controls->gamepad_index, key_bind.gamepad_key);
    }
    return result;
}

static bool operator==(FP_GameEntityHandle const &lhs, FP_GameEntityHandle const &rhs)
{
    bool result = lhs.id == rhs.id;
    return result;
}

static bool operator!=(FP_GameEntityHandle const &lhs, FP_GameEntityHandle const &rhs)
{
    bool result = !(lhs == rhs);
    return result;
}

static FP_GameCameraM2x3 FP_Game_CameraModelViewM2x3(FP_GameCamera camera)
{
    FP_GameCameraM2x3 result = {};
    result.model_view        = Dqn_M2x3_Identity();
    result.view_model        = Dqn_M2x3_Identity();

    Dqn_V2 center_offset = camera.size * .5f;
    Dqn_V2 rotate_origin = -camera.world_pos;
    result.model_view    = Dqn_M2x3_Mul(result.model_view, Dqn_M2x3_Translate(rotate_origin));
    result.model_view    = Dqn_M2x3_Mul(result.model_view, Dqn_M2x3_Rotate(camera.rotate_rads));
    result.model_view    = Dqn_M2x3_Mul(result.model_view, Dqn_M2x3_Scale(camera.scale));
    result.model_view    = Dqn_M2x3_Mul(result.model_view, Dqn_M2x3_Translate(center_offset));

    Dqn_V2 inverse_scale = Dqn_V2_InitNx1(1) / camera.scale;
    result.view_model    = Dqn_M2x3_Mul(result.view_model, Dqn_M2x3_Translate(-center_offset));
    result.view_model    = Dqn_M2x3_Mul(result.view_model, Dqn_M2x3_Scale(inverse_scale));
    result.view_model    = Dqn_M2x3_Mul(result.view_model, Dqn_M2x3_Rotate(-camera.rotate_rads));
    result.view_model    = Dqn_M2x3_Mul(result.view_model, Dqn_M2x3_Translate(-rotate_origin));

    #if 0
    Dqn_M2x3 identity = Dqn_M2x3_Mul(result.model_view, result.view_model);
    DQN_ASSERT(identity == Dqn_M2x3_Identity());
    #endif
    return result;
}

static FP_GameEntity *FP_Game_GetEntity(FP_Game *game, FP_GameEntityHandle handle)
{
    FP_GameEntity *result = nullptr;
    if (!game)
        return result;

    result                     = game->play.entities.data;
    uint64_t index_from_handle = handle.id & FP_GAME_ENTITY_HANDLE_INDEX_MASK;
    if (index_from_handle >= game->play.entities.size)
        return result;

    FP_GameEntity *candidate = game->play.entities.data + index_from_handle;
    if (candidate->handle == handle)
        result = candidate;
    return result;
}

static bool FP_Game_DFSPreOrderWalkEntityTree(FP_Game *game, FP_GameEntityIterator *it, FP_GameEntity *root)
{
    if (!game || !it || !root)
        return false;

    it->last_visited = it->entity;
    if (it->init) {
        it->iteration_count++;
    } else {
        it->init               = true;
        it->entity             = root;
        it->entity_parent      = it->entity->parent;
        it->entity_next        = it->entity->next;
        it->entity_first_child = it->entity->first_child;
    }

    if (!it->entity)
        return false;

    if (it->entity_first_child) {
        it->entity             = it->entity_first_child;
        it->entity_parent      = it->entity->parent;
        it->entity_next        = it->entity->next;
        it->entity_first_child = it->entity->first_child;
    } else {
        while (it->entity->handle != root->handle) {
            if (it->entity_next) {
                it->entity             = it->entity_next;
                it->entity_parent      = it->entity->parent;
                it->entity_next        = it->entity->next;
                it->entity_first_child = it->entity->first_child;
                break;
            } else {
                if (!it->entity_parent)
                    break;
                it->entity             = it->entity_parent;
                it->entity_parent      = it->entity->parent;
                it->entity_next        = it->entity->next;
                it->entity_first_child = it->entity->first_child;
            }
        }
    }

    return it->entity->handle != root->handle;
}

static bool FP_Game_DFSPostOrderWalkEntityTree(FP_Game *game, FP_GameEntityIterator *it, FP_GameEntity *root)
{
    if (!game || !it || !root)
        return false;

    bool ascending_tree = it->entity ? (it->last_visited == it->entity->last_child) : false;
    it->last_visited    = it->entity;

    if (it->init) {
        it->iteration_count++;
    } else {
        it->init               = true;
        it->entity             = root;
        it->entity_parent      = it->entity->parent;
        it->entity_next        = it->entity->next;
        it->entity_first_child = it->entity->first_child;
    }

    if (!it->entity)
        return false;

    // NOTE: Descend to deepest leaf node
    if (it->entity_first_child && !ascending_tree) {
        while (it->entity_first_child) {
            it->entity             = it->entity_first_child;
            it->entity_parent      = it->entity->parent;
            it->entity_next        = it->entity->next;
            it->entity_first_child = it->entity->first_child;
        }
    } else {
        // NOTE: We are at the leaf node, try going across
        if (it->entity != root && it->entity_next) {
            it->entity             = it->entity_next;
            it->entity_parent      = it->entity->parent;
            it->entity_next        = it->entity->next;
            it->entity_first_child = it->entity->first_child;
            ascending_tree         = false;
        }

        // NOTE: Try descend again
        if (it->entity_first_child && !ascending_tree) {
            while (it->entity_first_child) {
                it->entity             = it->entity_first_child;
                it->entity_parent      = it->entity->parent;
                it->entity_next        = it->entity->next;
                it->entity_first_child = it->entity->first_child;
            }
        }

        // NOTE: If we could not move further across or down then we've
        // exhausted the tree, start moving up.
        if (it->last_visited == it->entity) {
            it->entity             = it->entity_parent;
            it->entity_parent      = it->entity->parent;
            it->entity_next        = it->entity->next;
            it->entity_first_child = it->entity->first_child;
        }
    }

    return it->entity->handle != root->handle;
}


// NOTE: Parent entity
static void FP_Game_PushParentEntity(FP_Game *game, FP_GameEntityHandle handle)
{
    DQN_ASSERTF(game->play.parent_entity_stack.size >= 1, "Sentinel/nil entity has not been assigned as the 0th slot yet");
    if (game)
        Dqn_FArray_Add(&game->play.parent_entity_stack, handle);
}

static void FP_Game_PopParentEntity(FP_Game *game)
{
    // NOTE: 0th slot is reserved for the nil entity
    if (game && game->play.parent_entity_stack.size > 1)
        Dqn_FArray_PopBack(&game->play.parent_entity_stack, 1);
}

static FP_GameEntityHandle FP_Game_ActiveParentEntity(FP_Game const *game)
{
    FP_GameEntityHandle result = {};
    if (!game || !game->play.parent_entity_stack.size)
        return result;
    result = game->play.parent_entity_stack.data[game->play.parent_entity_stack.size - 1];
    return result;
}

static FP_GameEntity *FP_Game_ActiveParentEntityPointer(FP_Game const *game)
{
    FP_GameEntityHandle handle = FP_Game_ActiveParentEntity(game);
    FP_GameEntity *result      = FP_Game_GetEntity(DQN_CAST(FP_Game *)game, handle);
    return result;
}

static FP_GameEntity *FP_Game_MakeEntityPointerFV(FP_Game *game, DQN_FMT_ATTRIB char const *fmt, va_list args)
{
    FP_GameEntity *result = nullptr;
    if (!game)
        return result;

    DQN_ASSERTF(game->play.entities.size > 0, "Sentinel/nil entity has not been initialised yet");
    DQN_ASSERTF(game->play.root_entity, "Sentinel/nil entity has not been assigned yet");

    result = game->play.root_entity; // TODO(doyle): Root entity or ... the nil entity?
    if (game->play.entity_free_list) {
        result                      = game->play.entity_free_list;
        game->play.entity_free_list = game->play.entity_free_list->next;
        result->next                = nullptr;
    } else {
        if (game->play.entities.size > FP_GAME_ENTITY_HANDLE_INDEX_MAX)
            return result;

        result = Dqn_VArray_Make(&game->play.entities, Dqn_ZeroMem_Yes);
        if (!result)
            return result;
        result->handle.id = (game->play.entities.size - 1) & FP_GAME_ENTITY_HANDLE_INDEX_MASK;
    }

    result->sprite_height.meters             = 1;
    result->parent                           = FP_Game_ActiveParentEntityPointer(game);
    result->name                             = TELY_ChunkPool_AllocFmtFV(game->play.chunk_pool, fmt, args);
    result->buildings_visited                = FP_SentinelList_Init<FP_GameEntityHandle>(game->play.chunk_pool);
    result->action.sprite_alpha              = 1.f;
    result->stamina_cap                      = 93;
    result->stamina                          = result->stamina_cap;

    result->hp_cap                           = DQN_CAST(uint32_t)(FP_DEFAULT_DAMAGE * .8f);
    result->hp                               = result->hp_cap;

    result->inventory.airports_base_price    = 100;
    result->inventory.churchs_base_price     = 100;
    result->inventory.kennels_base_price     = 100;
    result->inventory.clubs_base_price       = 40;
    result->base_attack                      = FP_DEFAULT_DAMAGE;
    result->hp_recover_every_n_ticks         = 12;

    result->inventory.stamina_base_price     = 10;
    result->inventory.health_base_price      = 10;
    result->inventory.mobile_plan_base_price = 10;
    result->inventory.attack_base_price      = 10;


    // NOTE: Attach entity as a child to the parent
    FP_GameEntity *parent = result->parent;
    if (parent->first_child)
        parent->last_child->next = result;
    else
        parent->first_child = result;
    result->prev       = parent->last_child;
    parent->last_child = result;

    DQN_ASSERT(!result->next);
    DQN_ASSERT(result->handle.id);
    DQN_ASSERT(result->parent->handle == game->play.parent_entity_stack.data[game->play.parent_entity_stack.size - 1]);
    return result;
}

static FP_GameEntity *FP_Game_MakeEntityPointerF(FP_Game *game, DQN_FMT_ATTRIB char const *fmt, ...)
{
    va_list args;
    va_start(args, fmt);
    FP_GameEntity *result = FP_Game_MakeEntityPointerFV(game, fmt, args);
    va_end(args);
    return result;
}

static FP_GameEntityHandle FP_Game_MakeEntityF(FP_Game *game, DQN_FMT_ATTRIB char const *fmt, ...)
{
    va_list args;
    va_start(args, fmt);
    FP_GameEntity *entity = FP_Game_MakeEntityPointerF(game, fmt, args);
    va_end(args);

    FP_GameEntityHandle result = {};
    if (entity)
        result = entity->handle;
    return result;
}

static bool FP_Game_IsNilEntity(FP_GameEntity *entity)
{
    bool result = entity ? ((entity->handle.id & FP_GAME_ENTITY_HANDLE_INDEX_MASK) == 0) : true;
    return result;
}

static bool FP_Game_IsNilEntityHandle(FP_Game *game, FP_GameEntityHandle handle)
{
    bool result = true;
    if (handle.id != 0) {
        FP_GameEntity *entity = FP_Game_GetEntity(game, handle);
        result                = FP_Game_IsNilEntity(entity);
    }
    return result;
}

static void FP_Game_DetachEntityIntoFreeList(FP_Game *game, FP_GameEntityHandle handle)
{
    FP_GameEntity *entity = FP_Game_GetEntity(game, handle);
    if (FP_Game_IsNilEntity(entity))
        return;

    // NOTE: Entities in the entity tree always have a parent (except for the 
    // nil/root entity). If an entity is passed in to this function and there's
    // no parent, it's most likely you passed in an entity already in the free
    // list (in which case only the next pointer will be set). This is most
    // likely a mistake so we guard against it here.
    if (!DQN_CHECK(entity->parent))
        return;

    uint64_t const entity_index_from_handle = entity->handle.id & FP_GAME_ENTITY_HANDLE_INDEX_MASK;
    DQN_ASSERT(entity_index_from_handle < game->play.entities.size);

    uint64_t const entity_generation_raw    = entity->handle.id & FP_GAME_ENTITY_HANDLE_GENERATION_MASK;
    uint64_t const entity_generation        = entity_generation_raw >> FP_GAME_ENTITY_HANDLE_GENERATION_RSHIFT;
    uint64_t const new_entity_generation    = entity_generation + 1;

    // NOTE: De-attach entity from adjacent children
    if (entity->prev)
        entity->prev->next = entity->next;

    if (entity->next)
        entity->next->prev = entity->prev;

    // NOTE: De-attach from parent
    FP_GameEntity *parent = entity->parent;
    if (parent->first_child == entity)
        parent->first_child = entity->next;

    if (parent->last_child == entity)
        parent->last_child = entity->prev;

    if (entity->name.size)
        TELY_ChunkPool_Dealloc(game->play.chunk_pool, entity->name.data);

    FP_SentinelList_Deinit(&entity->spawn_list, game->play.chunk_pool);
    FP_SentinelList_Deinit(&entity->waypoints, game->play.chunk_pool);
    FP_SentinelList_Deinit(&entity->buildings_visited, game->play.chunk_pool);

    if (new_entity_generation > entity_generation) {
        // NOTE: Update the incremented handle disassociating all prior handles
        // to this entity which would reference older generation values
        *entity           = {};
        entity->parent    = game->play.root_entity;
        entity->handle.id = entity_index_from_handle | (new_entity_generation << FP_GAME_ENTITY_HANDLE_GENERATION_RSHIFT);

        // NOTE: Attach entity to the free list
        entity->next           = game->play.entity_free_list;
        entity->prev           = nullptr;
        game->play.entity_free_list = entity;
    } else {
        // NOTE: We've cycled through all possible generations for this handle
        // We will not increment it and freeze it so it is no longer allocated
        // out. This prevents code that is still holding onto *really* old
        // handles
    }
}

static void FP_Game_DeleteEntity(FP_Game *game, FP_GameEntityHandle handle)
{
    uint64_t index_from_handle = handle.id & FP_GAME_ENTITY_HANDLE_INDEX_MASK;
    if (!game || !DQN_CHECK(index_from_handle < game->play.entities.size))
        return;

    FP_GameEntity *root = game->play.entities.data + index_from_handle;
    if (root->handle != handle)
        return;

    // NOTE: The iterator snaps a copy of all the internal n-ary tree pointers
    // so as we delete we do not accidentally invalidate any of the pointers.
    for (FP_GameEntityIterator it = {}; FP_Game_DFSPostOrderWalkEntityTree(game, &it, root); ) {
        DQN_ASSERT(it.entity);
        DQN_ASSERT(it.entity != root);
        FP_GameEntity *entity = it.entity;
        FP_Game_DetachEntityIntoFreeList(game, entity->handle);
    }

    FP_Game_DetachEntityIntoFreeList(game, root->handle);
}

static Dqn_V2 FP_Game_CalcEntityWorldPos(FP_Game const *game, FP_GameEntityHandle handle)
{
    Dqn_V2 result = {};
    if (!game)
        return result;

    FP_GameEntity const *first = FP_Game_GetEntity(DQN_CAST(FP_Game *)game, handle);
    for (FP_GameEntity const *entity = first; entity != game->play.root_entity; entity = entity->parent)
        result += entity->local_pos;
    return result;
}

static Dqn_Rect FP_Game_CalcEntityLocalHitBox(FP_Game const *game, FP_GameEntityHandle handle)
{
    FP_GameEntity *entity    = FP_Game_GetEntity(DQN_CAST(FP_Game *)game, handle);
    Dqn_V2 half_hit_box_size = entity->local_hit_box_size * .5f;
    Dqn_Rect result          = Dqn_Rect_InitV2x2(entity->local_hit_box_offset - half_hit_box_size, entity->local_hit_box_size);
    return result;
}

static Dqn_Rect FP_Game_CalcEntityWorldHitBox(FP_Game const *game, FP_GameEntityHandle handle)
{
    FP_GameEntity *entity          = FP_Game_GetEntity(DQN_CAST(FP_Game *) game, handle);
    Dqn_V2           world_pos     = FP_Game_CalcEntityWorldPos(game, handle);
    Dqn_Rect         local_hit_box = FP_Game_CalcEntityLocalHitBox(game, entity->handle);
    Dqn_Rect         result        = Dqn_Rect_InitV2x2(world_pos + local_hit_box.pos, local_hit_box.size);
    return result;
}

static Dqn_Rect FP_Game_CalcEntityAttackWorldHitBox(FP_Game const *game, FP_GameEntityHandle handle)
{
    FP_GameEntity *entity      = FP_Game_GetEntity(DQN_CAST(FP_Game *) game, handle);
    Dqn_V2           world_pos = FP_Game_CalcEntityWorldPos(game, handle);
    Dqn_V2 half_hit_box_size   = entity->attack_box_size * .5f;
    Dqn_Rect result            = Dqn_Rect_InitV2x2(world_pos + entity->attack_box_offset - half_hit_box_size, entity->attack_box_size);
    return result;
}

static Dqn_FArray<Dqn_Rect, FP_GameDirection_Count> FP_Game_CalcEntityMeleeAttackBoxes(FP_Game const *game, FP_GameEntityHandle handle)
{
    Dqn_FArray<Dqn_Rect, FP_GameDirection_Count> result = {};
    Dqn_Rect hit_box                                    = FP_Game_CalcEntityWorldHitBox(game, handle);
    DQN_FOR_UINDEX (dir_index, FP_GameDirection_Count) {
        Dqn_Rect *rect = Dqn_FArray_Make(&result, Dqn_ZeroMem_Yes);
        rect->size     = hit_box.size;
        switch (dir_index) {
            case FP_GameDirection_Left: {
                rect->pos = Dqn_Rect_InterpolatedPoint(hit_box, Dqn_V2_InitNx2(-1.f, 0.f));
            } break;

            case FP_GameDirection_Right: {
                rect->pos = Dqn_Rect_InterpolatedPoint(hit_box, Dqn_V2_InitNx2(+1.f, 0.f));
            } break;

            case FP_GameDirection_Up: {
                rect->pos = Dqn_Rect_InterpolatedPoint(hit_box, Dqn_V2_InitNx2(0.f, -1.f));
            } break;

            case FP_GameDirection_Down: {
                rect->pos = Dqn_Rect_InterpolatedPoint(hit_box, Dqn_V2_InitNx2(0.f, +1.f));
            } break;

            case FP_GameDirection_Count: break;
        }
    }

    return result;
}

static Dqn_Rect FP_Game_CalcEntityArrayWorldBoundingBox(FP_Game const *game, FP_GameEntityHandle const *handles, Dqn_usize count)
{
    Dqn_Rect result = {};
    if (!game || !handles)
        return result;

    DQN_FOR_UINDEX(index, count) {
        FP_GameEntityHandle  handle = handles[index];
        FP_GameEntity const *entity = FP_Game_GetEntity(DQN_CAST(FP_Game *) game, handle);
        Dqn_Rect               bbox   = FP_Game_CalcEntityLocalHitBox(game, entity->handle);
        for (FP_GameShape const &shape_ : entity->shapes) {
            FP_GameShape const *shape = &shape_;
            switch (shape->type) {
                case FP_GameShapeType_None: {
                } break;

                case FP_GameShapeType_Circle: {
                    Dqn_Rect rect =
                        Dqn_Rect_InitV2x2(shape->p1 - shape->circle_radius, Dqn_V2_InitNx1(shape->circle_radius * 2.f));
                    bbox = Dqn_Rect_Union(bbox, rect);
                } break;

                case FP_GameShapeType_Rect: /*FALLTHRU*/
                case FP_GameShapeType_Line: {
                    Dqn_V2   min   = Dqn_V2_Min(shape->p1, shape->p2);
                    Dqn_V2   max   = Dqn_V2_Max(shape->p1, shape->p2);
                    Dqn_Rect rect  = Dqn_Rect_InitV2x2(min, max - min);

                    if (shape->type == FP_GameShapeType_Rect)
                        rect.pos -= rect.size * .5f;

                    bbox = Dqn_Rect_Union(bbox, rect);
                } break;
            }
        }
        bbox.pos += FP_Game_CalcEntityWorldPos(game, entity->handle);

        if (index)
            result = Dqn_Rect_Union(result, bbox);
        else
            result = bbox;
    }
    return result;
}

static Dqn_Rect FP_Game_CalcEntityWorldBoundingBox(FP_Game *game, FP_GameEntityHandle handle)
{
    Dqn_Rect result = FP_Game_CalcEntityArrayWorldBoundingBox(game, &handle, 1);
    return result;
}

// Reset the timers and animation for the current action and set the duration
// for the new action.
static void FP_Game_EntityActionReset(FP_Game *game, FP_GameEntityHandle entity_handle, uint64_t duration_ms, TELY_AssetAnimatedSprite sprite)
{
    FP_GameEntity *entity = FP_Game_GetEntity(game, entity_handle);
    if (!entity)
        return;
    entity->action.sprite              = sprite;
    entity->action.started_at_clock_ms = game->play.clock_ms;
    entity->action.end_at_clock_ms     = DQN_MAX(duration_ms, game->play.clock_ms + duration_ms);
}

static Dqn_V2I FP_Game_WorldPosToTilePos(FP_Game *game, Dqn_V2 world_pos)
{
    Dqn_V2I result = Dqn_V2I_InitNx2(world_pos.x / game->play.tile_size, world_pos.y / game->play.tile_size);
    return result;
}

static Dqn_V2 FP_Game_TilePosToWorldPos(FP_Game *game, Dqn_V2I tile_pos)
{
    Dqn_V2 result = Dqn_V2_InitNx2(tile_pos.x * game->play.tile_size, tile_pos.y * game->play.tile_size);
    return result;
}

static Dqn_V2 FP_Game_CalcWaypointWorldPos(FP_Game *game, FP_GameEntityHandle entity_handle, FP_GameWaypoint const *waypoint)
{
    Dqn_V2 result = {};
    if (!game || !waypoint)
        return result;

    FP_GameEntity *waypoint_entity = FP_Game_GetEntity(game, waypoint->entity);
    if (FP_Game_IsNilEntity(waypoint_entity))
        return result;

    // NOTE: We found a waypoint that is valid to move towards
    switch (waypoint->type) {
        case FP_GameWaypointType_At: {
            result = FP_Game_CalcEntityWorldPos(game, waypoint_entity->handle);
        } break;

        case FP_GameWaypointType_ClosestSide: /*FALLTHRU*/
        case FP_GameWaypointType_Side: {
            // NOTE: Sweep entity with half the radius of the source entity
            Dqn_Rect entity_hit_box   = FP_Game_CalcEntityWorldHitBox(game, entity_handle);
            Dqn_Rect waypoint_hit_box = FP_Game_CalcEntityWorldHitBox(game, waypoint_entity->handle);
            waypoint_hit_box.pos     -= (entity_hit_box.size * .5f);
            waypoint_hit_box.size    += entity_hit_box.size;

            Dqn_V2 side_pos_list[FP_GameDirection_Count] = {};
            side_pos_list[FP_GameDirection_Up]           = Dqn_V2_InitNx2(waypoint_hit_box.pos.x + waypoint_hit_box.size.w * .5f, waypoint_hit_box.pos.y - waypoint_hit_box.size.h * .1f);
            side_pos_list[FP_GameDirection_Down]         = Dqn_V2_InitNx2(waypoint_hit_box.pos.x + waypoint_hit_box.size.w * .5f, waypoint_hit_box.pos.y + waypoint_hit_box.size.h + waypoint_hit_box.size.h * .1f);
            side_pos_list[FP_GameDirection_Left]         = Dqn_V2_InitNx2(waypoint_hit_box.pos.x - waypoint_hit_box.size.w * .1f, waypoint_hit_box.pos.y + waypoint_hit_box.size.h * .5f);
            side_pos_list[FP_GameDirection_Right]        = Dqn_V2_InitNx2(waypoint_hit_box.pos.x + waypoint_hit_box.size.w + waypoint_hit_box.size.w * .1f, waypoint_hit_box.pos.y + waypoint_hit_box.size.h * .5f);

            if (waypoint->type == FP_GameWaypointType_Side) {
                result = side_pos_list[waypoint->type_direction];
            } else {
                Dqn_f32 best_dist = DQN_F32_MAX;
                for (Dqn_V2 target_pos : side_pos_list) {
                    Dqn_f32 dist_squared = Dqn_V2_LengthSq_V2x2(entity_hit_box.pos, target_pos);
                    if (dist_squared < best_dist) {
                        best_dist = dist_squared;
                        result    = target_pos;
                    }
                }
            }
        } break;

        case FP_GameWaypointType_Queue: {
            Dqn_ArrayFindResult<FP_GameEntityHandle> find_result = Dqn_FArray_Find<FP_GameEntityHandle>(&waypoint_entity->building_queue, entity_handle);
            Dqn_usize index_in_queue                             = find_result.index;
            Dqn_Rect waypoint_hit_box                            = FP_Game_CalcEntityWorldHitBox(game, waypoint_entity->handle);

            Dqn_V2 queue_starting_p = {};
            if (waypoint_entity->type == FP_EntityType_ClubTerry || waypoint_entity->type == FP_EntityType_ChurchTerry) {
                queue_starting_p = Dqn_Rect_InterpolatedPoint(waypoint_hit_box, Dqn_V2_InitNx2(0.5f, 1.1f));
            } else {
                queue_starting_p = Dqn_Rect_InterpolatedPoint(waypoint_hit_box, Dqn_V2_InitNx2(1.f, 1.1f));
            }

            Dqn_f32 queue_spacing   = FP_Game_MetersToPixelsNx1(game->play, 1.f);
            result                  = Dqn_V2_InitNx2(queue_starting_p.x - (queue_spacing * index_in_queue), queue_starting_p.y);
        } break;
    }

    result += waypoint->offset;
    return result;
}

FP_GameFindClosestEntityResult FP_Game_FindClosestEntityWithType(FP_Game *game, FP_GameEntityHandle src_entity_handle, FP_EntityType type)
{
    FP_GameFindClosestEntityResult result = {};
    FP_GameEntity *src_entity             = FP_Game_GetEntity(game, src_entity_handle);
    if (FP_Game_IsNilEntity(src_entity))
        return result;

    Dqn_V2 src_pos      = FP_Game_CalcEntityWorldPos(game, src_entity_handle);
    result.dist_squared = DQN_F32_MAX;
    result.pos          = Dqn_V2_InitNx1(DQN_F32_MAX);

    for (FP_GameEntityIterator it = {}; FP_Game_DFSPostOrderWalkEntityTree(game, &it, game->play.root_entity); ) {
        DQN_ASSERT(it.entity);
        FP_GameEntity *it_entity = it.entity;
        if (it_entity->type != type)
            continue;

        Dqn_V2 pos   = FP_Game_CalcEntityWorldPos(game, it_entity->handle);
        Dqn_f32 dist = Dqn_V2_LengthSq_V2x2(pos, src_pos);
        if (dist < result.dist_squared) {
            result.pos          = pos;
            result.dist_squared = dist;
            result.entity       = it_entity->handle;
        }
    }

    return result;
}

static FP_GameFindClosestEntityResult FP_Game_FindClosestEntityWithType(FP_Game *game, FP_GameEntityHandle src, FP_GameEntityHandle *entities, Dqn_usize size)
{
    FP_GameFindClosestEntityResult result = {};
    result.dist_squared = DQN_F32_MAX;
    result.pos          = Dqn_V2_InitNx1(DQN_F32_MAX);

    Dqn_V2 src_pos      = FP_Game_CalcEntityWorldPos(game, src);
    DQN_FOR_UINDEX (index, size) {
        FP_GameEntityHandle entity_handle = entities[index];
        FP_GameEntity *entity             = FP_Game_GetEntity(game, entity_handle);
        if (FP_Game_IsNilEntity(entity))
            continue;

        Dqn_V2 pos   = FP_Game_CalcEntityWorldPos(game, entity->handle);
        Dqn_f32 dist = Dqn_V2_LengthSq_V2x2(pos, src_pos);
        if (dist < result.dist_squared) {
            result.pos          = pos;
            result.dist_squared = dist;
            result.entity       = entity->handle;
        }
    }

    return result;
}

static bool FP_Game_CanEntityAttack(FP_GameEntity *entity, uint64_t current_time_ms)
{
    bool result = (current_time_ms - entity->last_attack_timestamp) >= entity->attack_cooldown_ms;
    return result;
}

static void FP_Game_EntityTransitionState(FP_Game *game, FP_GameEntity *entity, uint32_t desired_state)
{
    switch (entity->type) {
        case FP_EntityType_Perry: /*FALLTHRU*/
        case FP_EntityType_Terry: {
            if (desired_state == FP_EntityTerryState_Attack ||
                desired_state == FP_EntityTerryState_RangeAttack) {
                if (!FP_Game_CanEntityAttack(entity, game->play.clock_ms)) {
                    // NOTE: Cooldown not met do not transition
                    return;
                }
                entity->last_attack_timestamp = game->play.clock_ms;

                if (desired_state == FP_EntityTerryState_RangeAttack) {
                    if (entity->terry_mobile_data_plan < FP_TERRY_MOBILE_DATA_PER_RANGE_ATTACK)
                        return;
                }
            } else if (desired_state == FP_EntityTerryState_Dash) {
                if (entity->stamina < FP_TERRY_DASH_STAMINA_COST)
                    return;
            }
        } break;

        case FP_EntityType_Smoochie: {
            if (desired_state == FP_EntitySmoochieState_Attack) {
                if (!FP_Game_CanEntityAttack(entity, game->play.clock_ms)) {
                    // NOTE: Cooldown not met do not transition
                    return;
                }
                entity->last_attack_timestamp = game->play.clock_ms;
            }
        } break;

        case FP_EntityType_Clinger: {
            if (desired_state == FP_EntityClingerState_Attack) {
                if (!FP_Game_CanEntityAttack(entity, game->play.clock_ms)) {
                    // NOTE: Cooldown not met do not transition
                    return;
                }
                entity->last_attack_timestamp = game->play.clock_ms;
            }
        } break;

        case FP_EntityType_Catfish: {
            if (desired_state == FP_EntityClingerState_Attack) {
                if (!FP_Game_CanEntityAttack(entity, game->play.clock_ms)) {
                    // NOTE: Cooldown not met do not transition
                    return;
                }
                entity->last_attack_timestamp = game->play.clock_ms;
            }
        } break;


        case FP_EntityType_AirportTerry: {
        } break;

        case FP_EntityType_ChurchTerry: {
        } break;

        case FP_EntityType_ClubTerry: {
        } break;

        case FP_EntityType_Nil:
        case FP_EntityType_Heart:
        case FP_EntityType_KennelTerry:
        case FP_EntityType_Map:
        case FP_EntityType_MerchantGraveyard:
        case FP_EntityType_MerchantGym:
        case FP_EntityType_MerchantPhoneCompany:
        case FP_EntityType_MerchantTerry:
        case FP_EntityType_PhoneMessageProjectile:
        case FP_EntityType_Count: break;
        case FP_EntityType_AirportTerryPlane:
        case FP_EntityType_MobSpawner:
        case FP_EntityType_PortalMonkey: break;
        case FP_EntityType_Billboard: break;
    }
    // NOTE: If no returns are hit above we proceed with the state change
    entity->action.next_state = desired_state;
}

static void FP_GameRenderScanlines(TELY_Renderer *renderer,
                                   Dqn_f32        scanline_gap,
                                   Dqn_f32        scanline_thickness,
                                   Dqn_V2         screen_size)
{
    TELY_Render_PushTransform(renderer, Dqn_M2x3_Identity());
    DQN_DEFER { TELY_Render_PopTransform(renderer); };
    Dqn_f32 scanline_interval = scanline_gap + scanline_thickness;
    for (Dqn_f32 y = 0; y < screen_size.h; y += scanline_interval) {
        Dqn_V2 start = Dqn_V2_InitNx2(0, y);
        Dqn_V2 end   = Dqn_V2_InitNx2(screen_size.w, y);
        TELY_Render_LineColourV4(renderer, start, end, TELY_Colour_V4Alpha(TELY_COLOUR_WHITE_V4, 0.1f), scanline_thickness);
    }
}

static FP_GameCanMoveToPositionResult FP_Game_CanEntityMoveToPosition(FP_Game *game, FP_GameEntityHandle entity_handle, Dqn_V2 delta_pos)
{
    FP_GameCanMoveToPositionResult result = {};
    FP_GameEntity *entity                 = FP_Game_GetEntity(game, entity_handle);
    if (FP_Game_IsNilEntity(entity))
        return result;

    Dqn_Rect const entity_world_hit_box                    = FP_Game_CalcEntityWorldHitBox(game, entity->handle);
    Dqn_V2 const   entity_pos                              = FP_Game_CalcEntityWorldPos(game, entity->handle);
    Dqn_f32 const  SENTINEL_T                              = 999.f;
    Dqn_f32        global_earliest_t                       = SENTINEL_T;
    Dqn_V2         global_earliest_pos_just_before_collide = {};
    Dqn_V2 const   entity_new_pos                          = entity_pos + delta_pos;

    if ((entity->flags & FP_GameEntityFlag_NoClip) == 0) {
        for (FP_GameEntityIterator collider_it = {}; FP_Game_DFSPostOrderWalkEntityTree(game, &collider_it, game->play.root_entity);) {
            DQN_ASSERT(collider_it.entity);
            FP_GameEntity *collider = collider_it.entity;
            if (collider->handle == entity->handle)
                continue;

            // TODO(doyle): Calculate the list of collidables at the start of the frame
            if ((collider->flags & FP_GameEntityFlag_NonTraversable) == 0)
                continue;

            bool skip_colliding_with_player = false;
            for (FP_GameEntityHandle player : game->play.players) {
                if (player == collider->handle) {
                    skip_colliding_with_player = true;
                    break;
                }
            }

            if (skip_colliding_with_player)
                continue;

            bool entity_collides_with_collider = true;
            switch (entity->type) {
                case FP_EntityType_Catfish:  /*FALLTHRU*/
                case FP_EntityType_Smoochie: /*FALLTHRU*/
                case FP_EntityType_Clinger: {
                    if (collider->type == FP_EntityType_Smoochie || collider->type == FP_EntityType_Clinger || collider->type == FP_EntityType_Catfish) {
                        entity_collides_with_collider = false;
                    } else if (FP_Entity_IsBuildingForMobs(collider)) {
                        #if 0
                        // NOTE: We disable collision on buildings we have visited to avoid some
                        // problems ...
                        if (FP_SentinelList_Find(&entity->buildings_visited, collider->handle)) {
                            entity_collides_with_collider = false;
                        }
                        #else
                        entity_collides_with_collider = false;
                        #endif
                    } else if (collider->type == FP_EntityType_Heart ||
                               collider->type == FP_EntityType_MerchantGym ||
                               collider->type == FP_EntityType_MerchantTerry ||
                               collider->type == FP_EntityType_MerchantGraveyard ||
                               collider->type == FP_EntityType_MerchantPhoneCompany) {
                        entity_collides_with_collider = false;
                    }
                } break;

                case FP_EntityType_Perry: /*FALLTHRU*/
                case FP_EntityType_Terry: {
                    // NOTE: Don't collide with mobs when dashing (e.g. phase through)
                    FP_EntityTerryState state = *DQN_CAST(FP_EntityTerryState *)&entity->action.state;
                    if (state == FP_EntityTerryState_Dash || state == FP_EntityTerryState_DeadGhost) {
                        if (collider->type == FP_EntityType_Smoochie || collider->type == FP_EntityType_Clinger || collider->type == FP_EntityType_Catfish)
                            entity_collides_with_collider = false;
                    }
                } break;

                case FP_EntityType_Nil:                    break;
                case FP_EntityType_MerchantTerry:          break;
                case FP_EntityType_Count:                  break;
                case FP_EntityType_ClubTerry:              break;
                case FP_EntityType_Map:                    break;
                case FP_EntityType_MerchantGraveyard:      break;
                case FP_EntityType_MerchantGym:            break;
                case FP_EntityType_MerchantPhoneCompany:   break;
                case FP_EntityType_Heart:                  break;
                case FP_EntityType_AirportTerry:           break;
                case FP_EntityType_ChurchTerry:            break;
                case FP_EntityType_KennelTerry:            break;
                case FP_EntityType_PhoneMessageProjectile: break;
                case FP_EntityType_AirportTerryPlane:
                case FP_EntityType_MobSpawner:
                case FP_EntityType_PortalMonkey: break;
                case FP_EntityType_Billboard: break;
            }

            if (!entity_collides_with_collider)
                continue;

            // NOTE: Sweep collider with half the radius of the source entity
            Dqn_Rect collider_world_hit_box       = FP_Game_CalcEntityWorldHitBox(game, collider->handle);
            if (Dqn_V2_Area(collider_world_hit_box.size) <= 0)
                continue;

            Dqn_Rect swept_collider_world_hit_box = collider_world_hit_box;
            swept_collider_world_hit_box.pos      -= (entity_world_hit_box.size * .5f);
            swept_collider_world_hit_box.size     += entity_world_hit_box.size;

            if (!Dqn_Rect_ContainsPoint(swept_collider_world_hit_box, entity_new_pos))
                continue;

            Dqn_f32 collider_left_wall_x   = swept_collider_world_hit_box.pos.x;
            Dqn_f32 collider_right_wall_x  = swept_collider_world_hit_box.pos.x + swept_collider_world_hit_box.size.w;
            Dqn_f32 collider_top_wall_y    = swept_collider_world_hit_box.pos.y;
            Dqn_f32 collider_bottom_wall_y = swept_collider_world_hit_box.pos.y + swept_collider_world_hit_box.size.h;

            Dqn_V2 o = entity_pos;
            Dqn_V2 d = delta_pos;

            // NOTE: Solve collision by determining the 't' value at which
            // we hit one of the walls of the collider and move the entity
            // at exactly that point.
            // O + td = x
            // td     = x - O
            // t      = (x - O) / d

            Dqn_f32 earliest_t = SENTINEL_T;
            if (d.x != 0.f) {
                Dqn_f32 left_t  = (collider_left_wall_x  - o.x) / d.x;
                Dqn_f32 right_t = (collider_right_wall_x - o.x) / d.x;
                if (left_t >= 0.f && left_t <= 1.f)
                    earliest_t = DQN_MIN(earliest_t, left_t);
                if (right_t >= 0.f && right_t <= 1.f)
                    earliest_t = DQN_MIN(earliest_t, right_t);
            }

            if (d.y != 0.f) {
                Dqn_f32 top_t    = (collider_top_wall_y    - o.y) / d.y;
                Dqn_f32 bottom_t = (collider_bottom_wall_y - o.y) / d.y;
                if (top_t >= 0.f && top_t <= 1.f)
                    earliest_t = DQN_MIN(earliest_t, top_t);
                if (bottom_t >= 0.f && bottom_t <= 1.f)
                    earliest_t = DQN_MIN(earliest_t, bottom_t);
            }

            if (earliest_t < global_earliest_t) {
                global_earliest_t                       = earliest_t;
                global_earliest_pos_just_before_collide = entity_pos + (d * earliest_t);
            }
        }
    }

    result.yes = global_earliest_t == SENTINEL_T;
    if (!result.yes)
        result.next_closest_valid_move = delta_pos * global_earliest_t;
    return result;
}

static void FP_Game_MoveEntity(FP_Game *game, FP_GameEntityHandle entity_handle, Dqn_V2 acceleration_meters_per_s)
{
    // f"(t) = a
    // f'(t) = at + v
    // f (t) = 0.5f*a(t^2) + vt + p

    FP_GameEntity *entity = FP_Game_GetEntity(game, entity_handle);
    if (FP_Game_IsNilEntity(entity))
        return;

    Dqn_f32 t          = DQN_CAST(Dqn_f32)DQN_SQUARED(FP_GAME_PHYSICS_STEP);
    Dqn_f32 t_squared  = DQN_SQUARED(t);

    Dqn_f32 velocity_falloff_coefficient  = 0.82f;
    Dqn_f32 acceleration_feel_good_factor = 15'000.f;
    Dqn_V2  acceleration                  = FP_Game_MetersToPixelsV2(game->play, acceleration_meters_per_s) * acceleration_feel_good_factor;
    entity->velocity                      = (acceleration * t) + entity->velocity * velocity_falloff_coefficient;

    // NOTE: Zero out velocity with epsilon
    if (DQN_ABS(entity->velocity.x) < 5.f)
        entity->velocity.x = 0.f;
    if (DQN_ABS(entity->velocity.y) < 5.f)
        entity->velocity.y = 0.f;

    Dqn_V2 const delta_pos = (acceleration * 0.5f * t_squared) + (entity->velocity * t);
    FP_GameCanMoveToPositionResult move_to_result = FP_Game_CanEntityMoveToPosition(game, entity->handle, delta_pos);
    if (move_to_result.yes) {
        entity->local_pos += delta_pos;
    } else {
        entity->local_pos += move_to_result.next_closest_valid_move;
    }
}

static Dqn_Rect FP_Game_GetBuildingPlacementRectForEntity(FP_Game *game, FP_GamePlaceableBuilding placeable_building, FP_GameEntityHandle handle)
{
    Dqn_Rect       result = {};
    FP_GameEntity *entity = FP_Game_GetEntity(game, handle);
    if (FP_Game_IsNilEntity(entity))
        return result;

    FP_EntityRenderData render_data = FP_Entity_GetRenderData(game, placeable_building.type, placeable_building.state, entity->direction);
    Dqn_Rect box   = FP_Game_CalcEntityWorldHitBox(game, entity->handle);
    Dqn_V2 build_p = {};
    switch (entity->direction) {
        case FP_GameDirection_Up: {
            build_p = Dqn_Rect_InterpolatedPoint(box, Dqn_V2_InitNx2(0.5f, 0.f)) - Dqn_V2_InitNx2(0.f, render_data.render_size.h * .5f + 10.f);
        } break;

        case FP_GameDirection_Down: {
            build_p = Dqn_Rect_InterpolatedPoint(box, Dqn_V2_InitNx2(0.5f, 1.f)) + Dqn_V2_InitNx2(0.f, render_data.render_size.h * .5f + 10.f);
        } break;

        case FP_GameDirection_Left: {
            build_p = Dqn_Rect_InterpolatedPoint(box, Dqn_V2_InitNx2(0.0f, 0.5f)) - Dqn_V2_InitNx2(render_data.render_size.w * .5f + 10.f, 0);
        } break;

        case FP_GameDirection_Right: {
            build_p = Dqn_Rect_InterpolatedPoint(box, Dqn_V2_InitNx2(1.f, 0.5f)) + Dqn_V2_InitNx2(render_data.render_size.w * .5f + 10.f, 0);
        } break;

        case FP_GameDirection_Count: DQN_INVALID_CODE_PATH; break;
    }

    result.size = render_data.render_size;
    result.pos  = build_p - (render_data.render_size * .5f);
    return result;
}