/* blocks.c -- the kernel serves a node's block requests.  See blocks.h.
 *
 * This is the one file of v4's that includes v3's headers: every block goes
 * through v3's own calls.
 */
#include "v4/blocks.h"
#include "block_subsystem.h"

static void let_go(v4_blocks *w)
{
    unsigned i;
    for (i = 0; i < V4_BLOCK_SLOTS; i++) { w->block[i] = 0; w->changed[i] = 0; }
    w->next = 0;
    w->last = -1;
}

void v4_blocks_init(v4_blocks *w, v4_cell window)
{
    w->window = window;
    w->epoch = blk_subsys_epoch();
    let_go(w);
}

static v4_cell slot_addr(const v4_blocks *w, unsigned s)
{
    return w->window + (v4_cell)(s * V4_BLOCK_CELLS);
}

/* The block in slot s is written.  Whether or not storage takes it, it is
 * no longer marked. */
static int write_slot(v4_blocks *w, v4_node *n, unsigned s)
{
    uint8_t *b = blk_get_buffer(w->block[s], 1);
    v4_cell at = slot_addr(w, s);
    unsigned i;

    w->changed[s] = 0;
    if (!b) return V4_BLOCK_REFUSED;
    for (i = 0; i < V4_BLOCK_CELLS; i++) {
        v4_ucell c = (v4_ucell)n->mem[at + (v4_cell)i];
        b[4u * i] = (uint8_t)(c & 0xFFu);
        b[4u * i + 1u] = (uint8_t)((c >> 8) & 0xFFu);
        b[4u * i + 2u] = (uint8_t)((c >> 16) & 0xFFu);
        b[4u * i + 3u] = (uint8_t)((c >> 24) & 0xFFu);
    }
    return (blk_update(w->block[s]) == BLK_OK && blk_flush(w->block[s]) == BLK_OK) ? V4_BLOCK_OK : V4_BLOCK_REFUSED;
}

/* A slot to put a block in: an empty one, or one whose block is not marked,
 * or, with every one marked, the next in turn, its block written first.
 * *status is not V4_BLOCK_OK if that write was refused; the slot is empty
 * all the same. */
static unsigned take_slot(v4_blocks *w, v4_node *n, int *status)
{
    unsigned i, s;

    *status = V4_BLOCK_OK;
    for (i = 0; i < V4_BLOCK_SLOTS; i++) if (w->block[i] == 0) return i;
    for (i = 0; i < V4_BLOCK_SLOTS; i++) {
        s = (w->next + i) % V4_BLOCK_SLOTS;
        if (!w->changed[s]) break;
    }
    if (i == V4_BLOCK_SLOTS) {
        s = w->next;
        *status = write_slot(w, n, s);
    }
    w->next = (s + 1u) % V4_BLOCK_SLOTS;
    w->block[s] = 0;
    w->changed[s] = 0;
    if (w->last == (int)s) w->last = -1;
    return s;
}

/* BLOCK and BUFFER: ( n -- waddr status ) */
static void slot_for(v4_blocks *w, v4_node *n, int read)
{
    v4_cell num, at;
    uint32_t block;
    unsigned i, s;
    int status;

    if (n->ds.depth < 1u) { v4_dstack_reset(&n->ds); v4_dstack_push(&n->ds, 0); v4_dstack_push(&n->ds, (v4_cell)V4_BLOCK_REFUSED); return; }
    num = v4_dstack_pop(&n->ds);
    block = (uint32_t)num;
    if (num < 1 || (uint64_t)num > 0xFFFFFFFFull || !blk_is_valid(block)) {
        v4_dstack_push(&n->ds, 0); v4_dstack_push(&n->ds, (v4_cell)V4_BLOCK_RANGE);
        return;
    }
    for (s = 0; s < V4_BLOCK_SLOTS && w->block[s] != block; s++) { }
    if (s == V4_BLOCK_SLOTS) {
        const uint8_t *b = 0;
        s = take_slot(w, n, &status);
        if (status == V4_BLOCK_OK && read) {
            b = blk_get_buffer(block, 0);
            if (!b) status = V4_BLOCK_REFUSED;
        }
        if (status != V4_BLOCK_OK) { v4_dstack_push(&n->ds, 0); v4_dstack_push(&n->ds, (v4_cell)status); return; }
        at = slot_addr(w, s);
        for (i = 0; i < V4_BLOCK_CELLS; i++)
            n->mem[at + (v4_cell)i] = b ? (v4_cell)((v4_ucell)b[4u * i] | ((v4_ucell)b[4u * i + 1u] << 8)
                                                    | ((v4_ucell)b[4u * i + 2u] << 16) | ((v4_ucell)b[4u * i + 3u] << 24))
                                        : 0;
        w->block[s] = block;
        w->changed[s] = 0;
    }
    w->last = (int)s;
    v4_dstack_push(&n->ds, slot_addr(w, s));
    v4_dstack_push(&n->ds, (v4_cell)V4_BLOCK_OK);
}

int v4_blocks_serve(v4_blocks *w, v4_node *n, v4_cell request)
{
    unsigned s;
    int status = V4_BLOCK_OK;

    if (request > V4_REQ_BLOCK || request < V4_REQ_EMPTY_BUFFERS) return 0;

    /* the chain is not what it was: what the slots hold is of no chain now */
    if (blk_subsys_epoch() != w->epoch) { let_go(w); w->epoch = blk_subsys_epoch(); }

    if (request == V4_REQ_EMPTY_BUFFERS) { let_go(w); return 1; }

    /* the window is all in the node's memory, or nothing is done */
    if (!v4_node_addr_ok(w->window) || !v4_node_addr_ok(w->window + (v4_cell)(V4_BLOCK_SLOTS * V4_BLOCK_CELLS - 1u))) {
        if (request == V4_REQ_BLOCK || request == V4_REQ_BUFFER) {
            if (n->ds.depth >= 1u) (void)v4_dstack_pop(&n->ds);
            v4_dstack_push(&n->ds, 0);
        }
        v4_dstack_push(&n->ds, (v4_cell)V4_BLOCK_REFUSED);
        return 1;
    }

    if (request == V4_REQ_BLOCK)  { slot_for(w, n, 1); return 1; }
    if (request == V4_REQ_BUFFER) { slot_for(w, n, 0); return 1; }
    if (request == V4_REQ_UPDATE) {
        if (w->last >= 0 && w->block[w->last] != 0) w->changed[w->last] = 1;
    } else {                                         /* SAVE-BUFFERS */
        for (s = 0; s < V4_BLOCK_SLOTS; s++)
            if (w->block[s] != 0 && w->changed[s] && write_slot(w, n, s) != V4_BLOCK_OK) {
                status = V4_BLOCK_REFUSED;
                w->block[s] = 0;
                if (w->last == (int)s) w->last = -1;
            }
    }
    v4_dstack_push(&n->ds, (v4_cell)status);
    return 1;
}