#define HOST_CHANNEL_ID_NIL (N_ChannelId) { .gen = 0, .idx = 0 }
#define HOST_CHANNEL_ID_ALL (N_ChannelId) { .gen = U32_MAX, .idx = U32_MAX }

#define N_PacketMagic       0xd9e3b8b6
#define N_MaxPacketChunkLen 1024
#define N_MaxPacketLen      1280  /* Give enough space for msg chunk + header */

#define N_NumChannelLookupBins      512
#define N_NumMsgAssemblerLookupBins 16384

typedef i32 N_CmdKind; enum {
    HOST_CMD_KIND_NONE,

    HOST_CMD_KIND_TRY_CONNECT,
    HOST_CMD_KIND_CONNECT_SUCCESS,
    HOST_CMD_KIND_DISCONNECT,
    HOST_CMD_KIND_HEARTBEAT,
    HOST_CMD_KIND_WRITE
};

typedef i32 N_EventKind; enum {
    HOST_EVENT_KIND_NONE,

    HOST_EVENT_KIND_CHANNEL_OPENED,
    HOST_EVENT_KIND_CHANNEL_CLOSED,
    HOST_EVENT_KIND_MSG
};

typedef i32 N_WriteFlag; enum {
    HOST_WRITE_FLAG_NONE = 0,

    HOST_WRITE_FLAG_RELIABLE = (1 << 0)
};

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

Struct(N_Cmd) {
    N_CmdKind kind;
    N_ChannelId channel_id;

    u16 heartbeat_id;
    u16 heartbeat_ack_id;

    b32 write_reliable;
    String write_msg;


    N_Cmd *next;
};

Struct(N_Event) {
    N_EventKind kind;
    N_ChannelId channel_id;
    String msg;

    N_Event *next;
};

Struct(N_EventList) {
    N_Event *first;
    N_Event *last;
};

Struct(N_ChannelLookupBin) {
    struct host_channel *first;
    struct host_channel *last;
};

Struct(N_RcvBuffer) {
    Arena *arena;
    struct host_rcv_packet *first_packet;
    struct host_rcv_packet *last_packet;
};

Struct(N_SndPacket) {
    N_SndPacket *next;
    u64 seq;

    u64 data_len;
    u8 data[N_MaxPacketLen];
};

Struct(N_Host) {
    Arena *arena;

    P_Sock *sock;

    BuddyCtx *buddy;  /* For storing msg assembler data */

    Arena *cmd_arena;
    N_Cmd *first_cmd;
    N_Cmd *last_cmd;
    N_Cmd *first_free_cmd;

    Arena *channel_arena;
    struct host_channel *channels;
    struct host_channel *first_free_channel;
    u64 num_channels_reserved;

    N_SndPacket *first_free_packet;                                  /* Allocated in `arena` */
    struct host_msg_assembler *first_free_msg_assembler;                        /* Allocated in `arena` */

    N_ChannelLookupBin *channel_lookup_bins;                        /* Allocated in `arena` */
    u64 num_channel_lookup_bins;

    struct host_msg_assembler_lookup_bin *msg_assembler_lookup_bins;            /* Allocated in `arena` */
    u64 num_msg_assembler_lookup_bins;

    /* Double buffer for incoming data */
    P_Mutex rcv_buffer_write_mutex;
    N_RcvBuffer *rcv_buffer_read;
    N_RcvBuffer *rcv_buffer_write;

    u64 bytes_received;
    u64 bytes_sent;
};

/* ========================== *
 * Startup
 * ========================== */

Struct(N_StartupReceipt) { i32 _; };
N_StartupReceipt host_startup(void);

/* ========================== *
 * Host
 * ========================== */

N_Host *host_alloc(u16 listen_port);

void host_release(N_Host *host);

/* ========================== *
 * Queue
 * ========================== */

void host_queue_connect_to_address(N_Host *host, P_Address connect_address);

void host_queue_disconnect(N_Host *host, N_ChannelId channel_id);

void host_queue_write(N_Host *host, N_ChannelId channel_id, String msg, u32 flags);

/* ========================== *
 * Info
 * ========================== */

i64 host_get_channel_last_rtt_ns(N_Host *host, N_ChannelId channel_id);
INLINE b32 host_channel_id_eq(N_ChannelId a, N_ChannelId b) { return a.idx == b.idx && a.gen == b.gen; }
INLINE b32 host_channel_id_is_nil(N_ChannelId id) { return id.gen == 0 && id.idx == 0; }

/* ========================== *
 * Update
 * ========================== */

N_EventList host_update_begin(Arena *arena, N_Host *host);
void host_update_end(N_Host *host);