////////////////////////////////////////////////////////////
//~ Acquire

PP_Ent *PP_AcquireRawEnt(PP_Snapshot *ss, PP_Ent *parent, PP_EntKey key)
{
    Assert(parent->valid);
    Assert(ss->valid);
    Assert(ss == parent->ss);
    PP_Ent *ent;
    if (ss->first_free_ent > 0 && ss->first_free_ent < ss->num_ents_reserved)
    {
        /* Reuse from free list */
        ent = &ss->ents[ss->first_free_ent];
        ss->first_free_ent = ent->next_free;
    }
    else
    {
        /* Make new */
        ent = PushStructNoZero(ss->ents_arena, PP_Ent);
        ++ss->num_ents_reserved;
    }
    *ent = *PP_NilEnt();
    ent->ss = ss;
    ent->valid = 1;
    ent->owner = ss->client->player_id;
    ent->_is_xform_dirty = 1;
    ++ss->num_ents_allocated;

    PP_SetEntKey(ent, key);
    PP_Link(ent, parent);

    return ent;
}

/* Acquires a new entity that will not sync */
PP_Ent *PP_AcquireLocalEnt(PP_Ent *parent)
{
    PP_Snapshot *ss = parent->ss;
    PP_Ent *e = PP_AcquireRawEnt(ss, parent, PP_RandomKey());
    e->owner = ss->local_player;
    return e;
}

PP_Ent *PP_AcquireLocalEntWithKey(PP_Ent *parent, PP_EntKey key)
{
    PP_Snapshot *ss = parent->ss;
    PP_Ent *e = PP_AcquireRawEnt(ss, parent, key);
    e->owner = ss->local_player;
    return e;
}

/* Acquires a new entity to be synced to clients */
PP_Ent *PP_AcquireSyncSrcEnt(PP_Ent *parent)
{
    PP_Snapshot *ss = parent->ss;
    PP_Ent *e = PP_AcquireRawEnt(ss, parent, PP_RandomKey());
    PP_EnableProp(e, PP_Prop_SyncSrc);
    e->owner = ss->local_player;
    return e;
}

PP_Ent *PP_AcquireSyncSrcEntWithKey(PP_Ent *parent, PP_EntKey key)
{
    PP_Snapshot *ss = parent->ss;
    PP_Ent *e = PP_AcquireRawEnt(ss, parent, key);
    PP_EnableProp(e, PP_Prop_SyncSrc);
    e->owner = ss->local_player;
    return e;
}

/* Acquires a new entity that will sync with incoming net src ents containing key, and coming from the specified owner */
PP_Ent *PP_AcquireSyncDstEnt(PP_Ent *parent, PP_EntKey ent_id, PP_EntKey owner_id)
{
    PP_Snapshot *ss = parent->ss;
    PP_Ent *e = PP_AcquireRawEnt(ss, parent, ent_id);
    PP_EnableProp(e, PP_Prop_SyncDst);
    e->owner = owner_id;
    return e;
}

////////////////////////////////////////////////////////////
//~ Release

void PP_ReleaseRawEnt(PP_Ent *ent)
{
    PP_Snapshot *ss = ent->ss;
    /* Release children */
    PP_Ent *child = PP_EntFromKey(ss, ent->first);
    while (child->valid)
    {
        PP_Ent *next = PP_EntFromKey(ss, child->next);
        PP_ReleaseRawEnt(child);
        child = next;
    }

    /* Release uid */
    PP_SetEntKey(ent, PP_NilEntKey);

    /* Release */
    ent->valid = 0;
    ent->next_free = ss->first_free_ent;
    ss->first_free_ent = PP_IndexFromEnt(ss, ent);
    --ss->num_ents_allocated;
}

void PP_Release(PP_Ent *ent)
{
    PP_Snapshot *ss = ent->ss;
    PP_Ent *parent = PP_EntFromKey(ss, ent->parent);
    if (parent->valid)
    {
        PP_Unlink(ent);
    }
    PP_ReleaseRawEnt(ent);
}

void PP_ReleaseAllWithProp(PP_Snapshot *ss, PP_Prop prop)
{
    TempArena scratch = BeginScratchNoConflict();

    PP_Ent **ents_to_release = PushDry(scratch.arena, PP_Ent *);
    u64 ents_to_release_count = 0;
    for (u64 ent_index = 0; ent_index < ss->num_ents_reserved; ++ent_index)
    {
        PP_Ent *ent = &ss->ents[ent_index];
        if (ent->valid && PP_HasProp(ent, prop))
        {
            *PushStructNoZero(scratch.arena, PP_Ent *) = ent;
            ++ents_to_release_count;
        }
    }

    /* Release from snapshot */
    /* TODO: Breadth first iteration to only release parent entities (since
     * child entities will be released along with parent anyway) */
    for (u64 i = 0; i < ents_to_release_count; ++i)
    {
        PP_Ent *ent = ents_to_release[i];
        if (ent->valid && !ent->is_root && !PP_HasProp(ent, PP_Prop_Cmd) && !PP_HasProp(ent, PP_Prop_Player))
        {
            PP_Release(ent);
        }
    }

    EndScratch(scratch);
}

////////////////////////////////////////////////////////////
//~ Activate

void PP_ActivateEnt(PP_Ent *ent, u64 current_tick)
{
    PP_EnableProp(ent, PP_Prop_Active);
    ent->activation_tick = current_tick;
    ++ent->continuity_gen;
}

////////////////////////////////////////////////////////////
//~ Ent key

u32 PP_IndexFromEnt(PP_Snapshot *ss, PP_Ent *ent)
{
    return ent - ss->ents;
}

PP_Ent *PP_EntFromIndex(PP_Snapshot *ss, u32 index)
{
    if (index > 0 && index < ss->num_ents_reserved)
    {
        return &ss->ents[index];
    }
    else
    {
        return PP_NilEnt();
    }
}

PP_EntBin *PP_EntBinFromKey(PP_Snapshot *ss, PP_EntKey key)
{
    return &ss->key_bins[key.uid.lo % ss->num_key_bins];
}

/* NOTE: This should only really happen during ent allocation (it doesn't make sense for an allocated ent's key to change) */
void PP_SetEntKey(PP_Ent *ent, PP_EntKey key)
{
    PP_Snapshot *ss = ent->ss;
    PP_EntKey old_id = ent->key;
    if (!PP_EqEntKey(old_id, key))
    {
        /* Release old from lookup */
        if (!PP_IsNilEntKey(old_id))
        {
            PP_EntBin *bin = PP_EntBinFromKey(ss, old_id);
            u32 prev_index = 0;
            u32 next_index = 0;
            u32 search_index = bin->first;
            PP_Ent *prev = PP_NilEnt();
            PP_Ent *next = PP_NilEnt();
            PP_Ent *search = PP_EntFromIndex(ss, search_index);
            while (search->valid)
            {
                next_index = search->next_in_id_bin;
                next = PP_EntFromIndex(ss, next_index);
                if (PP_EqEntKey(search->key, old_id))
                {
                    break;
                }
                prev_index = search_index;
                prev = search;
                search_index = next_index;
                search = next;
            }

            /* Old key not in bin, this should be impossible. */
            Assert(search->valid);

            if (prev->valid)
            {
                prev->next_in_id_bin = next_index;
            }
            else
            {
                bin->first = next_index;
            }

            if (next->valid)
            {
                next->prev_in_id_bin = prev_index;
            }
            else
            {
                bin->last = prev_index;
            }
        }

        /* Insert new key into lookup */
        if (!PP_IsNilEntKey(key))
        {
#if IsRtcEnabled
            {
                PP_Ent *existing = PP_EntFromKey(ss, key);
                /* Collision should be extremely unlikely under normal circumstances, there's probably a logic error somewhere. */
                Assert(!existing->valid);
            }
#endif

            PP_EntBin *bin = PP_EntBinFromKey(ss, key);
            u32 ent_index = PP_IndexFromEnt(ss, ent);
            PP_Ent *last = PP_EntFromIndex(ss, bin->last);
            if (last->valid)
            {
                last->next_in_id_bin = ent_index;
                ent->prev_in_id_bin = bin->last;
            }
            else
            {
                bin->first = ent_index;
                ent->prev_in_id_bin = 0;
            }
            bin->last = ent_index;
        }

        ent->key = key;
    }

}

PP_Ent *PP_EntFromKey(PP_Snapshot *ss, PP_EntKey key)
{
    PP_Ent *result = PP_NilEnt();
    if (!PP_IsNilEntKey(key) && ss->valid)
    {
        PP_EntBin *bin = PP_EntBinFromKey(ss, key);
        for (PP_Ent *e = PP_EntFromIndex(ss, bin->first); e->valid; e = PP_EntFromIndex(ss, e->next_in_id_bin))
        {
            if (PP_EqEntKey(e->key, key))
            {
                result = e;
                break;
            }
        }
    }
    return result;
}

PP_EntKey PP_RandomKey(void)
{
    PP_EntKey result = ZI;
    result.uid = UidFromTrueRand();
    return result;
}

/* Returns the deterministic key of the contact constraint ent key that should be produced from e0 & e1 colliding */
PP_EntKey PP_ContactConstraintKeyFromContactingKeys(PP_EntKey player_id, PP_EntKey id0, PP_EntKey id1)
{
    PP_EntKey result = ZI;
    result.uid = PP_ContactBasisUid;
    result.uid = CombineUid(result.uid, player_id.uid);
    result.uid = CombineUid(result.uid, id0.uid);
    result.uid = CombineUid(result.uid, id1.uid);
    return result;
}

/* Returns the deterministic key of the debug contact constraint ent key that should be produced from e0 & e1 colliding */
PP_EntKey PP_CollisionDebugKeyFromKeys(PP_EntKey player_id, PP_EntKey id0, PP_EntKey id1)
{
    PP_EntKey result = ZI;
    result.uid = PP_CollisionDebugBasisUid;
    result.uid = CombineUid(result.uid, player_id.uid);
    result.uid = CombineUid(result.uid, id0.uid);
    result.uid = CombineUid(result.uid, id1.uid);
    return result;
}

/* Returns the deterministic key of the tile chunk that should be produced at chunk pos */
PP_EntKey PP_TileChunkKeyFromIndex(Vec2I32 chunk_index)
{
    PP_EntKey result = ZI;
    result.uid = PP_TileChunkBasisUid;
    result.uid = CombineUid(result.uid, UID(RandU64FromSeed(chunk_index.x), RandU64FromSeed(chunk_index.y)));
    return result;
}

////////////////////////////////////////////////////////////
//~ Query

PP_Ent *PP_FirstWithProp(PP_Snapshot *ss, PP_Prop prop)
{
    u64 count = ss->num_ents_reserved;
    PP_Ent *entities = ss->ents;
    for (u64 ent_index = 0; ent_index < count; ++ent_index)
    {
        PP_Ent *ent = &entities[ent_index];
        if (ent->valid && PP_HasProp(ent, prop))
        {
            return ent;
        }
    }
    return PP_NilEnt();
}

PP_Ent *PP_FirstWithAllProps(PP_Snapshot *ss, PP_PropArray props)
{
    u64 count = ss->num_ents_reserved;
    PP_Ent *entities = ss->ents;
    for (u64 ent_index = 0; ent_index < count; ++ent_index)
    {
        PP_Ent *ent = &entities[ent_index];
        if (ent->valid)
        {
            b32 all = 1;
            for (u64 i = 0; i < props.count; ++i)
            {
                if (!PP_HasProp(ent, props.props[i]))
                {
                    all = 0;
                    break;
                }
            }
            if (all)
            {
                return ent;
            }
        }
    }
    return PP_NilEnt();
}

////////////////////////////////////////////////////////////
//~ Tree

void PP_Link(PP_Ent *ent, PP_Ent *parent)
{
    PP_Snapshot *ss = ent->ss;

    PP_Ent *old_parent = PP_EntFromKey(ss, ent->parent);
    if (old_parent->valid)
    {
        /* Unlink from current parent */
        PP_Unlink(ent);
    }

    PP_EntKey ent_id = ent->key;
    PP_EntKey last_child_id = parent->last;
    PP_Ent *last_child = PP_EntFromKey(ss, last_child_id);
    if (last_child->valid)
    {
        ent->prev = last_child_id;
        last_child->next = ent_id;
    }
    else
    {
        parent->first = ent_id;
    }
    parent->last = ent_id;

    if (parent->is_root)
    {
        ent->is_top = 1;
        ent->top = ent_id;
    }
    else
    {
        ent->top = parent->top;
    }

    ent->parent = parent->key;
}

/* NOTE: PP_Ent will be dangling after calling this, should re-link to root ent. */
void PP_Unlink(PP_Ent *ent)
{
    PP_Snapshot *ss = ent->ss;

    PP_EntKey parent_id = ent->parent;
    PP_Ent *parent = PP_EntFromKey(ss, parent_id);
    PP_Ent *prev = PP_EntFromKey(ss, ent->prev);
    PP_Ent *next = PP_EntFromKey(ss, ent->next);

    /* Unlink from parent & siblings */
    if (prev->valid)
    {
        prev->next = next->key;
    }
    else
    {
        parent->first = next->key;
    }
    if (next->valid)
    {
        next->prev = prev->key;
    }
    else
    {
        parent->last = prev->key;
    }
    ent->prev = PP_NilEntKey;
    ent->next = PP_NilEntKey;
}

////////////////////////////////////////////////////////////
//~ Xform

void PP_MarkChildXformsDirty(PP_Snapshot *ss, PP_Ent *ent)
{
    for (PP_Ent *child = PP_EntFromKey(ss, ent->first); child->valid; child = PP_EntFromKey(ss, child->next))
    {
        if (child->_is_xform_dirty)
        {
            break;
        }
        else
        {
            child->_is_xform_dirty = 1;
            PP_MarkChildXformsDirty(ss, child);
        }
    }
}

Xform PP_XformFromEnt_(PP_Snapshot *ss, PP_Ent *ent)
{
    Xform xf;
    if (ent->_is_xform_dirty)
    {
        if (ent->is_top)
        {
            xf = ent->_local_xform;
        }
        else
        {
            PP_Ent *parent = PP_EntFromKey(ss, ent->parent);
            xf = PP_XformFromEnt_(ss, parent);
            xf = MulXform(xf, ent->_local_xform);
            ent->_xform = xf;
            ent->_is_xform_dirty = 0;
        }
        ent->_xform = xf;
        ent->_is_xform_dirty = 0;
    }
    else
    {
        xf = ent->_xform;
    }
    return xf;
}

Xform PP_XformFromEnt(PP_Ent *ent)
{
    Xform xf;
    if (ent->_is_xform_dirty)
    {
        if (ent->is_top)
        {
            xf = ent->_local_xform;
        }
        else
        {
            PP_Snapshot *ss = ent->ss;
            PP_Ent *parent = PP_EntFromKey(ss, ent->parent);
            xf = PP_XformFromEnt_(ss, parent);
            xf = MulXform(xf, ent->_local_xform);
            ent->_xform = xf;
            ent->_is_xform_dirty = 0;
        }
        ent->_xform = xf;
        ent->_is_xform_dirty = 0;
    }
    else
    {
        xf = ent->_xform;
    }
    return xf;
}

Xform PP_LocalXformFromEnt(PP_Ent *ent)
{
    return ent->_local_xform;
}

void PP_SetXform(PP_Ent *ent, Xform xf)
{
    if (!EqXform(xf, ent->_xform))
    {
        PP_Snapshot *ss = ent->ss;
        /* Update local xform */
        if (ent->is_top)
        {
            ent->_local_xform = xf;
        }
        else
        {
            PP_Ent *parent = PP_EntFromKey(ss, ent->parent);
            Xform parent_global = PP_XformFromEnt_(ss, parent);
            ent->_local_xform = MulXform(InvertXform(parent_global), xf);
        }
        ent->_xform = xf;
        ent->_is_xform_dirty = 0;
        PP_MarkChildXformsDirty(ss, ent);
    }
}

void PP_SetLocalXform(PP_Ent *ent, Xform xf)
{
    if (!EqXform(xf, ent->_local_xform))
    {
        ent->_local_xform = xf;
        ent->_is_xform_dirty = 1;
        PP_MarkChildXformsDirty(ent->ss, ent);
    }
}

////////////////////////////////////////////////////////////
//~ Movement

void PP_SetLinearVelocity(PP_Ent *ent, Vec2 velocity)
{
    if (PP_HasProp(ent, PP_Prop_Kinematic) || PP_HasProp(ent, PP_Prop_Dynamic))
    {
        ent->linear_velocity = ClampVec2Len(velocity, SIM_MAX_LINEAR_VELOCITY);
    }
}

void PP_SetAngularVelocity(PP_Ent *ent, f32 velocity)
{
    if (PP_HasProp(ent, PP_Prop_Kinematic) || PP_HasProp(ent, PP_Prop_Dynamic))
    {
        ent->angular_velocity = ClampF32(velocity, -SIM_MAX_ANGULAR_VELOCITY, SIM_MAX_ANGULAR_VELOCITY);
    }
}

void PP_ApplyLinearImpulse(PP_Ent *ent, Vec2 impulse, Vec2 point)
{
    if (PP_HasProp(ent, PP_Prop_Dynamic))
    {
        Xform xf = PP_XformFromEnt(ent);
        Vec2 center = xf.og;
        f32 scale = AbsF32(DeterminantFromXform(xf));
        f32 inv_mass = 1.f / (ent->mass_unscaled * scale);
        f32 inv_inertia = 1.f / (ent->inertia_unscaled * scale);

        Vec2 vcp = SubVec2(point, center);
        PP_SetLinearVelocity(ent, AddVec2(ent->linear_velocity, MulVec2(impulse, inv_mass)));
        PP_SetAngularVelocity(ent, WedgeVec2(vcp, impulse) * inv_inertia);
    }
}

void PP_ApplyLinearImpulseToCenter(PP_Ent *ent, Vec2 impulse)
{
    if (PP_HasProp(ent, PP_Prop_Dynamic))
    {
        Xform xf = PP_XformFromEnt(ent);
        f32 scale = AbsF32(DeterminantFromXform(xf));
        f32 inv_mass = 1.f / (ent->mass_unscaled * scale);

        PP_SetLinearVelocity(ent, AddVec2(ent->linear_velocity, MulVec2(impulse, inv_mass)));
    }
}

void PP_ApplyForceToCenter(PP_Ent *ent, Vec2 force)
{
    if (PP_HasProp(ent, PP_Prop_Dynamic))
    {
        ent->force = AddVec2(ent->force, force);
    }
}

void PP_ApplyAngularImpulse(PP_Ent *ent, f32 impulse)
{
    if (PP_HasProp(ent, PP_Prop_Dynamic))
    {
        Xform xf = PP_XformFromEnt(ent);
        f32 scale = AbsF32(DeterminantFromXform(xf));
        f32 inv_inertia = 1.f / (ent->inertia_unscaled * scale);
        PP_SetAngularVelocity(ent, ent->angular_velocity + impulse * inv_inertia);
    }
}

void PP_ApplyTorque(PP_Ent *ent, f32 torque)
{
    if (PP_HasProp(ent, PP_Prop_Dynamic))
    {
        ent->torque += torque;
    }
}

////////////////////////////////////////////////////////////
//~ Tile

PP_Ent *PP_TileChunkFromChunkIndex(PP_Snapshot *ss, Vec2I32 chunk_index)
{
    PP_EntKey chunk_id = PP_TileChunkKeyFromIndex(chunk_index);
    PP_Ent *chunk_ent = PP_EntFromKey(ss, chunk_id);
    return chunk_ent;
}

PP_Ent *PP_TileChunkFromWorldTileIndex(PP_Snapshot *ss, Vec2I32 world_tile_index)
{
    Vec2I32 chunk_index = PP_TileChunkIndexFromWorldTileIndex(world_tile_index);
    PP_Ent *chunk_ent = PP_TileChunkFromChunkIndex(ss, chunk_index);
    return chunk_ent;
}

PP_TileKind PP_TileKindFromChunk(PP_Ent *chunk_ent, Vec2I32 local_tile_index)
{
    PP_TileKind result = chunk_ent->tile_chunk_tiles[local_tile_index.x + (local_tile_index.y * SIM_TILES_PER_CHUNK_SQRT)];
    return result;
}

////////////////////////////////////////////////////////////
//~ Lerp

void PP_LerpEnt(PP_Ent *e, PP_Ent *e0, PP_Ent *e1, f64 blend)
{
    if (PP_IsValidAndActive(e0) && PP_IsValidAndActive(e1)
        && PP_EqEntKey(e0->key, e1->key)
        && e0->continuity_gen == e1->continuity_gen)
    {
        e->_local_xform = LerpXform(e0->_local_xform, e1->_local_xform, blend);

        if (e->is_top)
        {
            /* TODO: Cache parent & child xforms in sim */
            Xform e0_xf = PP_XformFromEnt(e0);
            Xform e1_xf = PP_XformFromEnt(e1);
            PP_SetXform(e, LerpXform(e0_xf, e1_xf, blend));
        }

        e->control_force = LerpF32(e0->control_force, e1->control_force, blend);
        e->control_torque = LerpF32(e0->control_torque, e1->control_torque, blend);

        e->linear_velocity = LerpVec2(e0->linear_velocity, e1->linear_velocity, blend);
        e->angular_velocity = LerpAngleF32(e0->angular_velocity, e1->angular_velocity, blend);

        e->control.move = LerpVec2(e0->control.move, e1->control.move, blend);
        e->control.focus = LerpVec2(e0->control.focus, e1->control.focus, blend);

        e->sprite_local_xform = LerpXform(e0->sprite_local_xform, e1->sprite_local_xform, blend);
        e->animation_last_frame_change_time_ns = LerpI64(e0->animation_last_frame_change_time_ns, e1->animation_last_frame_change_time_ns, (f64)blend);
        e->animation_frame = (u32)RoundF32ToI32(LerpF32(e0->animation_frame, e1->animation_frame, blend));

        e->camera_quad_xform = LerpXform(e0->camera_quad_xform, e1->camera_quad_xform, blend);
        e->camera_xform_target = LerpXform(e0->camera_xform_target, e1->camera_xform_target, blend);
        e->shake = LerpF32(e0->shake, e1->shake, blend);

        e->tracer_gradient_start = LerpVec2(e0->tracer_gradient_start, e1->tracer_gradient_start, blend);
        e->tracer_gradient_end = LerpVec2(e0->tracer_gradient_end, e1->tracer_gradient_end, blend);
    }
}

////////////////////////////////////////////////////////////
//~ Sync

/* Walks a local & remote ent tree and allocates any missing net dst ents from remote src ents */
void PP_CreateMissingEntsFromSnapshots(PP_Ent *local_parent, PP_Ent *remote, PP_EntKey remote_player)
{
    __prof;
    if (PP_HasProp(remote, PP_Prop_SyncSrc))
    {
        PP_Snapshot *local_ss = local_parent->ss;
        PP_Snapshot *remote_ss = remote->ss;

        PP_EntKey key = remote->key;
        PP_Ent *local_ent = PP_EntFromKey(local_ss, key);
        if (!local_ent->valid)
        {
            local_ent = PP_AcquireSyncDstEnt(local_parent, key, remote_player);
        }
        for (PP_Ent *remote_child = PP_EntFromKey(remote_ss, remote->first); remote_child->valid; remote_child = PP_EntFromKey(remote_ss, remote_child->next))
        {
            PP_CreateMissingEntsFromSnapshots(local_ent, remote_child, remote_player);
        }
    }
}

/* Copies data between two synced entities */
void PP_SyncEnt(PP_Ent *local, PP_Ent *remote)
{
    PP_Ent old = *local;
    CopyStruct(local, remote);

    /* Why would 2 ents w/ different uids ever be synced? */
    Assert(PP_EqEntKey(local->key, old.key));

    local->ss = old.ss;
    local->key = old.key;

    /* Keep local tree */
    local->parent = old.parent;
    local->prev = old.prev;
    local->next = old.next;
    local->first = old.first;
    local->last = old.last;
    local->top = old.top;
    local->owner = old.owner;

    /* Keep indices */
    local->next_in_id_bin = old.next_in_id_bin;
    local->prev_in_id_bin = old.prev_in_id_bin;
    local->next_free = old.next_free;

    PP_DisableProp(local, PP_Prop_SyncSrc);
    PP_EnableProp(local, PP_Prop_SyncDst);
}

#if 1

////////////////////////////////////////////////////////////
//~ Encode

void PP_EncodeEnt(BB_Writer *bw, PP_Ent *e0, PP_Ent *e1)
{
    PP_Snapshot *ss = e1->ss;
    /* FIXME: Things like xforms need to be retreived manually rather than memcopied. */

    /* TODO: Granular delta encoding */

    u64 pos = 0;
    e1->ss = e0->ss;
    while (pos < sizeof(*e1))
    {
        u64 chunk_size = MinU64(pos + 8, sizeof(*e1)) - pos;
        u8 *chunk0 = (u8 *)e0 + pos;
        u8 *chunk1 = (u8 *)e1 + pos;
        if (BB_WriteBit(bw, !EqBytes(chunk0, chunk1, chunk_size)))
        {
            u64 bits = 0;
            CopyBytes(&bits, chunk1, chunk_size);
            BB_WriteUBits(bw, bits, 64);
        }
        pos += 8;
    }
    e1->ss = ss;
}

////////////////////////////////////////////////////////////
//~ Decode

void PP_DecodeEnt(BB_Reader *br, PP_Ent *e)
{
    PP_Snapshot *old_ss = e->ss;
    {
        u64 pos = 0;
        while (pos < sizeof(*e))
        {
            u8 *chunk = (u8 *)e + pos;
            if (BB_ReadBit(br))
            {
                u64 chunk_size = MinU64(pos + 8, sizeof(*e)) - pos;
                u64 bits = BB_ReadUBits(br, 64);
                CopyBytes(chunk, &bits, chunk_size);
            }
            pos += 8;
        }
    }
    e->ss = old_ss;

}

#else

////////////////////////////////////////////////////////////
//~ Encode

void PP_EncodeEnt(BB_Writer *bw, PP_Ent *e0, PP_Ent *e1)
{
    PP_Snapshot *ss = e1->ss;


    /* FIXME: Things like xforms need to be retreived manually rather than memcopied.
     * This will also be true for things like ent keys once uids are implemented. */

     /* TODO: Granular delta encoding */

    u64 pos = 0;
    e1->ss = e0->ss;
    while (pos < sizeof(*e1))
    {
        u64 chunk_size = MinU64(pos + 8, sizeof(*e1)) - pos;
        u8 *chunk0 = (u8 *)e0 + pos;
        u8 *chunk1 = (u8 *)e1 + pos;
        if (EqBytes(chunk0, chunk1, chunk_size))
        {
            BB_WriteBit(bw, 0);
        }
        else
        {
            BB_WriteBit(bw, 1);
            u64 bits = 0;
            CopyBytes(&bits, chunk1, chunk_size);
            BB_WriteUBits(bw, bits, 64);
        }
        pos += 8;
    }
    e1->ss = ss;
}

////////////////////////////////////////////////////////////
//~ Decode

void PP_DecodeEnt(BB_Reader *br, PP_Ent *e)
{
    PP_Ent decoded = *e;
    {
        u64 pos = 0;
        while (pos < sizeof(decoded))
        {
            u8 *chunk = (u8 *)&decoded + pos;
            if (BB_ReadBit(br))
            {
                u64 chunk_size = MinU64(pos + 8, sizeof(decoded)) - pos;
                u64 bits = BB_ReadUBits(br, 64);
                CopyBytes(chunk, &bits, chunk_size);
            }
            pos += 8;
        }
    }
    decoded.ss = e->ss;

    PP_EntKey old_id = e->key;
    PP_EntKey new_id = decoded.key;
    CopyStruct(e, &decoded);
    e->key = old_id;
    if (!PP_EqEntKey(old_id, new_id))
    {
        PP_SetEntKey(e, new_id);
    }
}
#endif