////////////////////////////////////////////////////////////
//~ Id types

Struct(EntityId)
{
    Uid uid;
};

Struct(ClientHandle)
{
    u32 idx;
    u32 gen;
};

#define NilClientHandle ((ClientHandle) { .gen = 0, .idx = 0 })


////////////////////////////////////////////////////////////
//~ Client store types

Struct(ClientLookupBin)
{
    struct ClientHandle first;
    struct ClientHandle last;
};

Struct(ClientStore)
{
    b32 valid;
    Arena *arena;

    /* Client lookup */
    ClientLookupBin *client_lookup_bins;
    u64 num_client_lookup_bins;

    /* Clients */
    Arena *clients_arena;
    struct Client *clients;
    ClientHandle first_free_client;
    u64 num_clients_allocated;
    u64 num_clients_reserved;
};

Inline ClientStore *sim_client_store_nil(void)
{
    extern Readonly ClientStore **_g_sim_client_store_nil;
    return *_g_sim_client_store_nil;
}

////////////////////////////////////////////////////////////
//~ Client types

Struct(SnapshotLookupBin)
{
    struct Snapshot *first;
    struct Snapshot *last;
};

Struct(Client)
{
    b32 valid;
    ClientHandle handle;
    ClientStore *store;

    Arena *snapshots_arena;

    /* Round trip time of the client (if networked) */
    i64 last_rtt_ns;

    N_ChannelId channel_id;
    u64 channel_hash;

    ClientHandle next_free;
    ClientHandle next_in_bin;
    ClientHandle prev_in_bin;

    /* The client's player entity id in the master sim (if relevant) */
    EntityId player_id;

    /* This is the highest confirmed tick of ours that we know this client has received */
    u64 ack;

    /* This is the highest confirmed ack of ours that we know this client has received (this
     * can be used to determine which client ticks will no longer be delta encoded from and
     * therefore can be released) */
    u64 double_ack;

    /* This is the highest tick of their's that we have received */
    u64 highest_received_tick;

    /* Snapshots sorted by tick (low to high) */
    u64 first_tick;
    u64 last_tick;
    u64 num_ticks;
    struct Snapshot *first_free_snapshot;

    /* Tick -> snapshot lookup */
    u64 num_snapshot_lookup_bins;
    SnapshotLookupBin *snapshot_lookup_bins;
};

Inline Client *NilClient(void)
{
    extern Readonly Client **_g_sim_client_nil;
    return *_g_sim_client_nil;
}

Inline b32 EqClientHandle(ClientHandle a, ClientHandle b)
{
    return a.gen == b.gen && a.idx == b.idx;
}

////////////////////////////////////////////////////////////
//~ Layer types

/* Absolute layers */
#define Layer_FloorDecals   (-300)
#define Layer_Bullets       (-200)
#define Layer_Tracers       (-100)
#define Layer_Shoulders     (0)
#define Layer_Walls         (100)

/* Relative layers */
#define Layer_DefaultRelative     (0)
#define Layer_RelativeWeapon      (1)

////////////////////////////////////////////////////////////
//~ Control types

Enum(ControlFlag)
{
    ControlFlag_Fire            = 1 << 0,
    ControlFlag_AltFire         = 1 << 1,

    /* Testing */
    ControlFlag_Drag            = 1 << 2,
    ControlFlag_Delete          = 1 << 3,
    ControlFlag_ClearAll        = 1 << 4,
    ControlFlag_SpawnTest1      = 1 << 5,
    ControlFlag_SpawnTest2      = 1 << 6,
    ControlFlag_SpawnTest3      = 1 << 7,
    ControlFlag_SpawnTest4      = 1 << 8,
    ControlFlag_TestWalls       = 1 << 9,
    ControlFlag_TestTiles       = 1 << 10,
    ControlFlag_TestExplode     = 1 << 11,
    ControlFlag_TestTeleport    = 1 << 12,
};

Struct(ControlData)
{
    Vec2 move;         /* Movement direction vector (speed of 0 -> 1) */
    Vec2 focus;        /* Focus direction vector (where does the controller want to look) */
    Vec2 dbg_cursor;   /* Where is the user's cursor in the world (used for things like editing the world) */
    ControlFlag flags;
};

Enum(CmdKind)
{
    CmdKind_Invalid,

    CmdKind_Control,
    CmdKind_Chat
};

////////////////////////////////////////////////////////////
//~ Tile types

Enum(TileKind)
{
    TileKind_None,
    TileKind_Wall,

    TileKind_Count
};
StaticAssert(TileKind_Count < 256);  /* Tile kind must fit in 8 bits */

////////////////////////////////////////////////////////////
//~ Snapshot types

Enum(SyncFlag)
{
    SyncFlag_NoSyncPredictables = 1 << 0
};

Struct(Snapshot)
{
    b32 valid;
    u64 tick;
    Client *client;
    Snapshot *next_free;
    Snapshot *next_in_bin;
    Snapshot *prev_in_bin;
    u64 prev_tick;
    u64 next_tick;

    Arena *arena;

    /* Sim time (guaranteed to increase by sim_dt_ns each step) */
    i64 sim_dt_ns;
    i64 sim_time_ns;

    /* If != previous tick's continuity then don't lerp */
    u64 continuity_gen;

    /* The last physics iteration (used for tracking contact lifetime) */
    u64 phys_iteration;

    /* The id of the receiver's player in the snapshot */
    EntityId local_player;

    /* Id lookup */
    struct EntBin *id_bins;
    u64 num_id_bins;

    /* Entities */
    Arena *ents_arena;
    struct Entity *ents;
    u32 first_free_ent;
    u32 num_ents_allocated;
    u32 num_ents_reserved;
};

Inline Snapshot *NilSnapshot(void)
{
    extern Readonly Snapshot **_g_sim_snapshot_nil;
    return *_g_sim_snapshot_nil;
}

////////////////////////////////////////////////////////////
//~ State types

#define ClientLookupBinsCount 127
#define TickLookupBinsCount 127
#define IdLookupBinsCount 4096

Struct(SharedSimCtx)
{
    Arena *nil_arena;
    ClientStore *nil_client_store;
    Client *nil_client;
    Snapshot *nil_snapshot;
    struct Entity *nil_ent;
};

extern SharedSimCtx shared_sim_ctx;

/* Accessed via `sim_client_store_nil()` */
extern Readonly ClientStore **_g_sim_client_store_nil;

/* Accessed via `NilClient()` */
extern Readonly Client **_g_sim_client_nil;

/* Accessed via `NilSnapshot()` */
extern Readonly Snapshot **_g_sim_snapshot_nil;
extern Readonly struct Entity **_g_sim_ent_nil;

////////////////////////////////////////////////////////////
//~ Startup

void StartupSim(void);

////////////////////////////////////////////////////////////
//~ Client store acquire operations

ClientStore *AcquireClientStore(void);
void ReleaseClientStore(ClientStore *store);

////////////////////////////////////////////////////////////
//~ Client acquire operations

Client *AcquireClient(ClientStore *store);
void ReleaseClient(Client *client);

////////////////////////////////////////////////////////////
//~ Client lookup operations

u64 ClientChannelHashFromChannelId(N_ChannelId channel_id);
void SetClientChannelId(Client *client, N_ChannelId channel_id);
Client *ClientFromChannelId(ClientStore *store, N_ChannelId channel_id);
Client *ClientFromHandle(ClientStore *store, ClientHandle handle);

////////////////////////////////////////////////////////////
//~ Snapshot acquire operations

Snapshot *AcquireSnapshot(Client *client, Snapshot *src, u64 tick);
void ReleaseSnapshot(Snapshot *ss);
void ReleaseSnapshotsInRange(Client *client, u64 start, u64 end);

////////////////////////////////////////////////////////////
//~ Snapshot lookup operations

Snapshot *SnapshotFromTick(Client *client, u64 tick);
Snapshot *SnapshotFromClosestTickLte(Client *client, u64 tick);
Snapshot *SnapshotFromClosestTickGte(Client *client, u64 tick);

////////////////////////////////////////////////////////////
//~ Tile operations

Vec2I32 WorldTileIndexFromPos(Vec2 pos);
Vec2 PosFromWorldTileIndex(Vec2I32 world_tile_index);
Vec2I32 LocalTileIndexFromWorldTileIndex(Vec2I32 world_tile_index);
Vec2I32 WorldTileIndexFromLocalTileIndex(Vec2I32 tile_chunk_index, Vec2I32 local_tile_index);
Vec2I32 TileChunkIndexFromWorldTileIndex(Vec2I32 world_tile_index);
void SetSnapshotTile(Snapshot *ss, Vec2I32 world_tile_index, TileKind tile_kind);

////////////////////////////////////////////////////////////
//~ Snapshot lerp operations

Snapshot *AcquireSnapshotFromLerp(Client *client, Snapshot *ss0, Snapshot *ss1, f64 blend);

////////////////////////////////////////////////////////////
//~ Snapshot sync operations

void SyncSnapshotEntities(Snapshot *local_ss, Snapshot *remote_ss, EntityId remote_player, u32 sync_flags);

////////////////////////////////////////////////////////////
//~ Snapshot encode operations

void EncodeSnapshot(BB_Writer *bw, Client *receiver, Snapshot *ss0, Snapshot *ss1);

////////////////////////////////////////////////////////////
//~ Snapshot decode operations

void DecodeSnapshot(BB_Reader *br, Snapshot *ss);