/*
  StarForth — Steady-State Virtual Machine Runtime

  Copyright (c) 2023–2025 Robert A. James
  All rights reserved.

  This file is part of the StarForth project.

  Licensed under the StarForth License, Version 1.0 (the "License");
  you may not use this file except in compliance with the License.

  You may obtain a copy of the License at:
      https://github.com/star.4th@proton.me/StarForth/LICENSE.txt

  This software is provided "AS IS", WITHOUT WARRANTY OF ANY KIND,
  express or implied, including but not limited to the warranties of
  merchantability, fitness for a particular purpose, and noninfringement.

 See the License for the specific language governing permissions and
 limitations under the License.

 */

/**
 * stadium.h - The Stadium cell and header (FABRIC.md §3, punch list item 3.1)
 *
 * A cell is one of exactly two things: a patron header, or a continuation
 * cell owned by exactly one patron. The union is closed, two-valued, and
 * fixed at build time -- not a type field. See FABRIC.md §3.
 */

#ifndef STARKERNEL_VM_STADIUM_H
#define STARKERNEL_VM_STADIUM_H

#ifdef __STARKERNEL__

#include <stdint.h>

#define STADIUM_CELL_BYTES 64

/*
 * StadiumPatronHeader - one member of the closed two-valued cell union
 * (FABRIC.md §3). Nine wires: identity, heat, TTL, pin (a bit in `flags`),
 * link, code field (`behaviour`), mass, payload, contains. `flags` bit 0 is
 * `pin`; the remaining bits are reserved. `behaviour` is the closed code-field
 * enumeration (§18.3) -- not yet defined, item 3.3's scope.
 *
 * Field order is largest-to-smallest so natural C99 alignment adds zero
 * padding: every offset below is already a multiple of that field's own
 * alignment, and the struct's total size (64) is a multiple of its max
 * alignment (8), so no compiler inserts trailing padding either. Do not
 * reorder without re-checking this holds on all three ISAs.
 */
typedef struct {
    uint64_t identity;     /* offset 0  -- handle or name, never a content hash while resident (§24.4) */
    uint64_t heat;         /* offset 8  -- Q48.16, conserved share of 1.0 (§19.1) */
    uint32_t ttl;          /* offset 16 -- remaining lifetime; messages and ACLs only (§17.1) */
    uint32_t link;         /* offset 20 -- index into the Stadium, not a pointer */
    uint32_t contains;     /* offset 24 -- index of the patron held inside this one, or none (item 1.1) */
    uint16_t mass;         /* offset 28 -- cells this patron occupies (§19.2) */
    uint8_t  flags;        /* offset 30 -- bit 0 = pin; remaining bits reserved */
    uint8_t  behaviour;    /* offset 31 -- code field, closed enumeration (§18.3) */
    uint8_t  payload[32];  /* offset 32 -- inline payload, used when mass == 1 */
} StadiumPatronHeader;

/*
 * StadiumContinuationCell - the other member of the union. Owned by exactly
 * one patron header, chained by `next`. Never ranked, never reaped, never
 * dispatched (§3) -- pure floor space, accounted for in its owner's mass.
 */
typedef struct {
    uint32_t next;          /* offset 0 -- index of the next continuation cell, or none */
    uint8_t  payload[60];   /* offset 4 */
} StadiumContinuationCell;

/*
 * StadiumCell - the closed two-valued union itself (§3). Which member is
 * valid for a given array slot is NOT stored in the cell -- FABRIC.md's item
 * 3.1 amendment to §3 rules this an external side bitmap, one bit per cell,
 * kept outside the cell array. Declared here as the indexing contract this
 * type expects; item 3.2 (boot-time allocation) allocates the bitmap itself.
 */
typedef union {
    StadiumPatronHeader     header;
    StadiumContinuationCell continuation;
} StadiumCell;

/* C99-portable compile-time size assertions (no _Static_assert -- that's C11). */
typedef char stadium_header_size_check[(sizeof(StadiumPatronHeader) == STADIUM_CELL_BYTES) ? 1 : -1];
typedef char stadium_continuation_size_check[(sizeof(StadiumContinuationCell) == STADIUM_CELL_BYTES) ? 1 : -1];
typedef char stadium_cell_size_check[(sizeof(StadiumCell) == STADIUM_CELL_BYTES) ? 1 : -1];

#endif /* __STARKERNEL__ */

#endif /* STARKERNEL_VM_STADIUM_H */