/*
  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.
*/

/**
 * log_region.c - Growable per-VM log-persistence ring on Artemis's disk.
 * See starkernel/log_region.h for the format/interface design.
 *
 * Deliberately never calls log_message() (or anything documented to call
 * it) -- this runs inside Artemis's own dictionary context during message
 * delivery (LOG-APPEND, dispatched by a sender's MSG-SEND/MSG-TICK); a log
 * call here would append to Artemis's own buffer and eventually flush back
 * through this same path.
 */

#include "starkernel/log_region.h"

#include <stddef.h>
#include <string.h>

#include "block_subsystem.h" /* blk_meta_zone_read/write, compute_crc64 */

static uint64_t log_region_ctrl_compute_crc(const log_region_ctrl_t *ctrl) {
    size_t crc_span = offsetof(log_region_ctrl_t, hdr_crc);
    return compute_crc64((const uint8_t *)ctrl, crc_span);
}

/* Reads the control header; returns 0 and *out populated only if magic,
 * version, and CRC all check out. Any other result (blank, foreign,
 * corrupt, or a read failure) is treated identically by the caller: "not
 * yet initialized," matching genesis_marker_read()'s own discipline. */
static int log_region_ctrl_read(log_region_ctrl_t *out) {
    if (blk_meta_zone_read(LOG_REGION_DEVBLOCK_FROM_TOP_BASE, (uint8_t *)out) != 0) return -1;
    if (LOG_REGION_GET_MAGIC(out->magic) != (uint32_t)(LOG_REGION_MAGIC & 0xFFFFFFFFull)) return -1;
    if (LOG_REGION_GET_VERSION(out->magic) != LOG_REGION_VERSION_0) return -1;
    uint64_t want_crc = log_region_ctrl_compute_crc(out);
    if (want_crc != out->hdr_crc) return -1;
    return 0;
}

static int log_region_ctrl_write(log_region_ctrl_t *ctrl) {
    ctrl->hdr_crc = log_region_ctrl_compute_crc(ctrl);
    return blk_meta_zone_write(LOG_REGION_DEVBLOCK_FROM_TOP_BASE, (const uint8_t *)ctrl) == 0 ? 0 : -1;
}

static void log_region_ctrl_init_fresh(log_region_ctrl_t *ctrl) {
    memset(ctrl, 0, sizeof(*ctrl));
    ctrl->magic     = LOG_REGION_PACK(LOG_REGION_VERSION_0);
    ctrl->devblocks = LOG_REGION_INITIAL_DEVBLOCKS;
    ctrl->head_slot = 0;
    ctrl->tail_slot = 0;
    ctrl->record_count = 0;
}

/* Reads/writes the devblock holding slot_index (LOG_SLOTS_PER_DEVBLOCK
 * slots per devblock), one devblock_from_top past the control header for
 * every LOG_SLOTS_PER_DEVBLOCK slots. */
static uint32_t log_region_slot_devblock_from_top(uint32_t slot_index) {
    return LOG_REGION_DEVBLOCK_FROM_TOP_BASE + 1u + (slot_index / LOG_SLOTS_PER_DEVBLOCK);
}

static int log_region_read_slot(uint32_t slot_index, log_slot_t *out) {
    uint8_t devblock_buf[4096];
    uint32_t dft = log_region_slot_devblock_from_top(slot_index);
    uint32_t slot_in_devblock = slot_index % LOG_SLOTS_PER_DEVBLOCK;

    if (blk_meta_zone_read(dft, devblock_buf) != 0) return -1;
    memcpy(out, devblock_buf + (size_t)slot_in_devblock * LOG_SLOT_SIZE, sizeof(*out));
    return 0;
}

static int log_region_write_slot(uint32_t slot_index, const log_slot_t *slot) {
    uint8_t devblock_buf[4096];
    uint32_t dft = log_region_slot_devblock_from_top(slot_index);
    uint32_t slot_in_devblock = slot_index % LOG_SLOTS_PER_DEVBLOCK;

    /* Read-modify-write: blk_meta_zone_*() only operates at whole-devblock
     * granularity, and a devblock holds LOG_SLOTS_PER_DEVBLOCK slots, so a
     * single-slot write must preserve its siblings. A read failure on a
     * never-yet-written devblock (blank fence content) is not fatal here --
     * proceed with a zeroed buffer, matching zuse_eligibility.c's own
     * "blank fence content is indistinguishable from absent, treat as
     * absent" discipline. */
    if (blk_meta_zone_read(dft, devblock_buf) != 0) {
        memset(devblock_buf, 0, sizeof(devblock_buf));
    }
    memcpy(devblock_buf + (size_t)slot_in_devblock * LOG_SLOT_SIZE, slot, sizeof(*slot));
    return blk_meta_zone_write(dft, devblock_buf) == 0 ? 0 : -1;
}

int log_region_append(uint8_t level, uint64_t timestamp,
                       const char *source, uint32_t source_len,
                       const char *msg, uint32_t msg_len) {
    log_region_ctrl_t ctrl;
    if (log_region_ctrl_read(&ctrl) != 0) {
        log_region_ctrl_init_fresh(&ctrl);
    }

    uint32_t total_slots = ctrl.devblocks * LOG_SLOTS_PER_DEVBLOCK;
    if (ctrl.record_count >= total_slots) {
        if (ctrl.devblocks < LOG_REGION_MAX_DEVBLOCKS) {
            /* Grow: new slots appear at indices [old_total_slots ..
             * new_total_slots-1], nothing already written moves -- safe
             * to do at any point in the ring's lifecycle regardless of
             * wrap state, since head/tail are slot INDICES modulo
             * total_slots, and the modulus is simply larger from here on. */
            ctrl.devblocks += LOG_REGION_GROWTH_INCREMENT;
            if (ctrl.devblocks > LOG_REGION_MAX_DEVBLOCKS) ctrl.devblocks = LOG_REGION_MAX_DEVBLOCKS;
            total_slots = ctrl.devblocks * LOG_SLOTS_PER_DEVBLOCK;
        }
        if (ctrl.record_count >= total_slots) {
            /* Still full (growth ceiling already reached) -- evict oldest,
             * unless doing so would discard higher-priority history for a
             * lower-priority newcomer (FABRIC-3.md §XXXII.4, 2026-09-15:
             * plain FIFO eviction here was flagged as level-blind -- a
             * flood of INFO/DEBUG noise could push out real ERROR/WARN
             * records). Read the oldest slot's own level before evicting:
             * if it's ERROR/WARN and the incoming record is not, protect
             * it -- drop the incoming record instead of evicting real
             * history. Any other combination (oldest is already low
             * priority, or the incoming record is itself ERROR/WARN)
             * evicts exactly as before. A read failure on the oldest slot
             * (should not happen -- it was written by this same function)
             * falls back to the prior unconditional-eviction behavior
             * rather than wedging the ring. */
            log_slot_t oldest;
            int oldest_protected = 0;
            if (log_region_read_slot(ctrl.head_slot, &oldest) == 0) {
                oldest_protected = (oldest.level <= LOG_REGION_PROTECTED_MAX_LEVEL);
            }
            int incoming_protected = (level <= LOG_REGION_PROTECTED_MAX_LEVEL);
            if (oldest_protected && !incoming_protected) {
                return 1; /* dropped by design, not a failure -- see header */
            }
            ctrl.head_slot = (ctrl.head_slot + 1u) % total_slots;
            ctrl.record_count--;
        }
    }

    log_slot_t slot;
    memset(&slot, 0, sizeof(slot));
    slot.timestamp = timestamp;
    slot.level     = level;

    uint32_t src_n = source_len;
    if (src_n > LOG_SLOT_SOURCE_MAX) src_n = LOG_SLOT_SOURCE_MAX;
    memcpy(slot.source, source, src_n);

    uint32_t msg_n = msg_len;
    if (msg_n > LOG_SLOT_MSG_MAX) msg_n = LOG_SLOT_MSG_MAX;
    memcpy(slot.msg, msg, msg_n);
    slot.msg_len = (uint16_t)msg_n;

    if (log_region_write_slot(ctrl.tail_slot, &slot) != 0) return -1;

    ctrl.tail_slot = (ctrl.tail_slot + 1u) % total_slots;
    if (ctrl.record_count < total_slots) ctrl.record_count++;

    return log_region_ctrl_write(&ctrl);
}