/* node.c -- the v4 node.  See node.h. */
#include "v4/node.h"
#include <stddef.h>

void v4_node_reset(v4_node *n)
{
    n->p = 0;
    n->a = 0;
    n->b = 0;
    for (unsigned i = 0; i < V4_NODE_WORDS; i++) n->mem[i] = 0;
    v4_guard_fill(n->mem_guard_head, V4_MEM_BOUND, V4_GUARD_PATTERN_HEAD);
    v4_guard_fill(n->mem_guard_tail, V4_MEM_BOUND, V4_GUARD_PATTERN_TAIL);
    v4_dstack_reset(&n->ds);
    v4_rstack_reset(&n->rs);
    v4_node_console_attach(n, -1);
    v4_node_console_input_attach(n, -1, -1);
    v4_node_fault_attach(n, -1);
    v4_node_stack_regs_attach(n, -1, -1);
    v4_node_error_attach(n, -1);
    v4_node_port_attach(n, -1);
}

void v4_node_error_attach(v4_node *n, v4_cell addr)
{
    n->error_reg = addr;
}

int v4_node_addr_ok(v4_cell addr)
{
    /* One unsigned compare covers both ends: a negative address is a very
     * large unsigned one. */
    return (v4_ucell)addr < (v4_ucell)V4_NODE_WORDS;
}

void v4_node_stack_regs_attach(v4_node *n, v4_cell d, v4_cell r)
{
    n->dstack_reg = d;
    n->rstack_reg = r;
}

void v4_node_fault_attach(v4_node *n, v4_cell table)
{
    n->fault_vector = (v4_node_addr_ok(table) && v4_node_addr_ok(table + (v4_cell)(V4_FAULT_KINDS - 1u))) ? table : (v4_cell)-1;
    n->fault_addr = 0;
    n->fault_kind = 0;
    n->faults = 0;
    n->stopped = 0;
}

void v4_node_fault(v4_node *n, unsigned kind, v4_cell addr)
{
    n->fault_kind = kind;
    n->fault_addr = addr;
    n->faults++;
    v4_rstack_clear(&n->rs);
    if (kind != V4_FAULT_RAISED) v4_dstack_clear(&n->ds);
    if (n->fault_vector >= 0) n->p = n->fault_vector + (v4_cell)kind;
    else n->stopped = 1;
}

int v4_node_guards_intact(const v4_node *n)
{
    return v4_guard_intact(n->mem_guard_head, V4_MEM_BOUND, V4_GUARD_PATTERN_HEAD)
        && v4_guard_intact(n->mem_guard_tail, V4_MEM_BOUND, V4_GUARD_PATTERN_TAIL)
        && v4_dstack_guards_intact(&n->ds)
        && v4_rstack_guards_intact(&n->rs);
}

v4_cell v4_node_load(const v4_node *n, v4_cell addr)
{
    if (!v4_node_addr_ok(addr)) return 0;
    return n->mem[(unsigned)addr];
}

void v4_node_store(v4_node *n, v4_cell addr, v4_cell value)
{
    /* CONSOLE-TX: capture the character, leave memory alone.  console_tx is
     * -1 when no console is attached, which no valid address equals. */
    if (addr == n->console_tx) {
        if (n->console_len < V4_CONSOLE_CAP)
            n->console[n->console_len++] = (unsigned char)((v4_ucell)value & 0xFFu);
        else
            n->console_dropped++;
        return;
    }
    /* A port: the node keeps what it wrote and is blocked until its
     * neighbour has taken it. */
    {
        int port = v4_node_port_index(n, addr);
        if (port >= 0 && port < (int)V4_PORTS) {
            n->request = value;
            n->ask_port = (unsigned)port;
            n->asking = 1;
            return;
        }
        if (port >= 0) { v4_node_fault(n, V4_FAULT_ADDRESS, addr); return; }   /* "any" and "which port" are not written to */
    }
    /* The stack registers: a store empties the stack.  -1 when not attached. */
    if (addr == n->dstack_reg) { v4_dstack_clear(&n->ds); return; }
    if (addr == n->rstack_reg) { v4_rstack_clear(&n->rs); return; }
    if (!v4_node_addr_ok(addr)) return;
    n->mem[(unsigned)addr] = value;
    /* NODE-ERROR: a non-zero code raises an error.  -1 when not attached. */
    if (addr == n->error_reg && value != 0) v4_node_fault(n, V4_FAULT_RAISED, value);
}

v4_cell v4_node_fetch(v4_node *n, v4_cell addr)
{
    /* console_rx and console_status are -1 when no input is attached, which
     * no valid address equals. */
    if (addr == n->console_status)
        return n->input_pos < n->input_len ? (v4_cell)-1 : (v4_cell)0;
    if (addr == n->console_rx) {
        v4_cell c;
        if (n->input_pos >= n->input_len) return (v4_cell)-1;
        c = (v4_cell)n->input[n->input_pos++];
        if (n->input_pos == n->input_len) n->input_pos = n->input_len = 0;
        return c;
    }
    {
        int port = v4_node_port_index(n, addr);
        if (port == (int)V4_PORTS + 1) return (v4_cell)n->last_from;
        if (port == (int)V4_PORTS + 2) { n->since_look = 0; return (v4_cell)n->writers; }
        if (port == (int)V4_PORTS + 3) { n->since_look = 0; return (v4_cell)n->readers; }
        if (port >= 0) {
            /* the word its neighbour wrote; v4_node_read_ready has said it is there */
            if (!n->given) return 0;
            n->given = 0;
            if (port == (int)V4_PORT_ANY) n->last_from = n->given_port;
            return n->given_value;
        }
    }
    if (addr == n->dstack_reg) return (v4_cell)n->ds.depth;
    if (addr == n->rstack_reg) return (v4_cell)n->rs.depth;
    return v4_node_load(n, addr);
}

void v4_node_console_input_attach(v4_node *n, v4_cell rx, v4_cell status)
{
    n->console_rx = rx;
    n->console_status = status;
    n->input_len = 0;
    n->input_pos = 0;
}

unsigned v4_node_console_feed(v4_node *n, const void *chars, unsigned len)
{
    const unsigned char *c = (const unsigned char *)chars;
    unsigned i, pending = n->input_len - n->input_pos, took = 0;

    /* Slide what is pending to the front so the whole buffer is usable. */
    if (n->input_pos > 0) {
        for (i = 0; i < pending; i++) n->input[i] = n->input[n->input_pos + i];
        n->input_pos = 0;
        n->input_len = pending;
    }
    while (took < len && n->input_len < V4_CONSOLE_CAP) n->input[n->input_len++] = c[took++];
    return took;
}

void v4_node_console_attach(v4_node *n, v4_cell addr)
{
    n->console_tx = addr;
    n->console_len = 0;
    n->console_dropped = 0;
}

void v4_node_port_attach(v4_node *n, v4_cell base)
{
    n->port = base;
    n->asking = 0;
    n->request = 0;
    n->ask_port = 0;
    n->reading = 0;
    n->read_port = 0;
    n->given = 0;
    n->given_value = 0;
    n->given_port = 0;
    n->last_from = 0;
    n->writers = 0;
    n->readers = 0;
    n->since_look = 0;
}

void v4_node_port_status(v4_node *n, unsigned writers, unsigned readers)
{
    n->writers = writers;
    n->readers = readers;
}

int v4_node_port_index(const v4_node *n, v4_cell addr)
{
    if (n->port < 0 || addr < n->port || addr > n->port + (v4_cell)V4_PORTS + 3) return -1;
    return (int)(addr - n->port);
}

int v4_node_read_ready(v4_node *n, v4_cell addr)
{
    int port = v4_node_port_index(n, addr);
    if (port < 0 || port > (int)V4_PORT_ANY) return 1;
    if (n->given && (port == (int)V4_PORT_ANY || (unsigned)port == n->given_port)) return 1;
    n->reading = 1;
    n->read_port = (unsigned)port;
    return 0;
}

void v4_node_port_give(v4_node *n, unsigned port, v4_cell value)
{
    n->given = 1;
    n->given_value = value;
    n->given_port = port;
    n->reading = 0;
}

void v4_node_born(v4_node *n, v4_cell base)
{
    v4_node_reset(n);
    v4_node_port_attach(n, base);
    n->p = base + (v4_cell)V4_PORT_ANY;
}

void v4_node_port_served(v4_node *n)
{
    n->asking = 0;
    n->since_look++;
}

unsigned v4_node_words_since_look(const v4_node *n)
{
    return n->since_look;
}

int v4_node_port_gone(v4_node *n, v4_cell code)
{
    if (code == 0 || n->error_reg < 0 || n->fault_vector < 0 || n->stopped) return 0;
    if (n->asking) n->asking = 0;
    else if (n->reading && !n->given && n->read_port != V4_PORT_ANY) n->reading = 0;
    else return 0;
    v4_node_store(n, n->error_reg, code);            /* raises it: P is the node's handler now */
    return 1;
}