/* wire.c -- a queue of whole messages.  See wire.h.
 *
 * Nothing here uses the C library: the bare-metal kernel links this file.
 */
#include "v4/wire.h"
#include "v4/message.h"

void v4_wire_reset(v4_wire_queue *q)
{
    unsigned i;
    for (i = 0; i < V4_WIRE_CELLS; i++) q->cell[i] = 0;
    q->head = 0;
    q->used = 0;
    q->mark = 0;
    q->arrived = 0;
    q->freed = 0;
    q->looked = 0;
}

unsigned v4_wire_cells(v4_cell length)
{
    if (length < 0 || length > (v4_cell)V4_MSG_MAX_CHARS) return 0;
    return V4_WIRE_HEADER + ((unsigned)length + 3u) / 4u;
}

/* the cell `off` cells from the front */
static unsigned slot(const v4_wire_queue *q, unsigned off)
{
    unsigned s = q->head + off;
    return s >= V4_WIRE_CELLS ? s - V4_WIRE_CELLS : s;
}

/* the cells the message `off` cells from the front takes */
static unsigned size_at(const v4_wire_queue *q, unsigned off)
{
    return v4_wire_cells(q->cell[slot(q, off + 6u)]);
}

int v4_wire_room(const v4_wire_queue *q, unsigned cells)
{
    return cells <= V4_WIRE_CELLS - q->used ? V4_WIRE_DONE : V4_WIRE_NO_ROOM;
}

/* `n` cells, already checked to fit, onto the back */
static unsigned back(v4_wire_queue *q, unsigned n)
{
    unsigned at = q->used;
    q->used += n;
    q->arrived = 1;
    return at;
}

int v4_wire_put(v4_wire_queue *q, const v4_cell *header7, const v4_cell *text)
{
    unsigned n = v4_wire_cells(header7[6]), at, i;
    if (n == 0) return V4_WIRE_NOT_A_MESSAGE;
    if (v4_wire_room(q, n) != V4_WIRE_DONE) return V4_WIRE_NO_ROOM;
    at = back(q, n);
    for (i = 0; i < V4_WIRE_HEADER; i++) q->cell[slot(q, at + i)] = header7[i];
    for (; i < n; i++) q->cell[slot(q, at + i)] = text[i - V4_WIRE_HEADER];
    return V4_WIRE_DONE;
}

void v4_wire_first(v4_wire_queue *q)
{
    q->looked = 0;
    q->mark = 0;
}

int v4_wire_next(v4_wire_queue *q)
{
    q->looked = 0;
    if (q->mark >= q->used) return V4_WIRE_NO_MESSAGE;
    q->mark += size_at(q, q->mark);
    return q->mark < q->used ? V4_WIRE_DONE : V4_WIRE_NO_MESSAGE;
}

int v4_wire_look(v4_wire_queue *q, v4_cell *header7)
{
    unsigned i;
    if (q->mark >= q->used) return V4_WIRE_NO_MESSAGE;
    for (i = 0; i < V4_WIRE_HEADER; i++) header7[i] = q->cell[slot(q, q->mark + i)];
    q->looked = 1;
    return V4_WIRE_DONE;
}

/* the marked message is off the queue; the mark is at the one that followed */
static void remove_marked(v4_wire_queue *q)
{
    unsigned n = size_at(q, q->mark), i;
    if (q->mark == 0) {
        q->head = slot(q, n);
    } else {
        for (i = q->mark; i + n < q->used; i++) q->cell[slot(q, i)] = q->cell[slot(q, i + n)];
    }
    q->used -= n;
    q->freed = 1;
    q->looked = 0;
}

int v4_wire_take(v4_wire_queue *q, v4_cell *header7, v4_cell *text, unsigned text_cap)
{
    unsigned n, i;
    if (q->mark >= q->used) return V4_WIRE_NO_MESSAGE;
    n = size_at(q, q->mark);
    if (n - V4_WIRE_HEADER > text_cap) return V4_WIRE_NOT_A_MESSAGE;
    for (i = 0; i < V4_WIRE_HEADER; i++) header7[i] = q->cell[slot(q, q->mark + i)];
    for (; i < n; i++) text[i - V4_WIRE_HEADER] = q->cell[slot(q, q->mark + i)];
    remove_marked(q);
    return V4_WIRE_DONE;
}

int v4_wire_drop(v4_wire_queue *q)
{
    if (q->mark >= q->used) return V4_WIRE_NO_MESSAGE;
    remove_marked(q);
    return V4_WIRE_DONE;
}

int v4_wire_move(v4_wire_queue *from, v4_wire_queue *to)
{
    unsigned n, at, i;
    if (from->mark >= from->used) return V4_WIRE_NO_MESSAGE;
    n = size_at(from, from->mark);
    if (from == to || v4_wire_room(to, n) != V4_WIRE_DONE) return V4_WIRE_NO_ROOM;
    at = back(to, n);
    for (i = 0; i < n; i++) to->cell[slot(to, at + i)] = from->cell[slot(from, from->mark + i)];
    to->cell[slot(to, at + 3u)] = (v4_cell)((v4_ucell)from->cell[slot(from, from->mark + 3u)] - 1u);   /* in the unsigned type: no overflow at the least cell */
    remove_marked(from);
    return V4_WIRE_DONE;
}