/*
 * bug-1864: the vtaskmgr dispatcher checked each queued task's endpoint
 * "busy" flag one item at a time while the vcpu finishing that endpoint's
 * previous message cleared the flag without the queue lock. Within ONE
 * scan, task N was skipped (endpoint still busy), the endpoint unblocked,
 * and task N+1 for the SAME endpoint was then dequeued first -- a standby
 * processed WAL entry seq 258 before 257 and NACKed (log-mismatch storms).
 *
 * vtask_deq_eligible() takes the busy check as a parameter so these tests
 * can make an endpoint unblock part-way through a scan, deterministically.
 */
#include <stdlib.h>
#include <string.h>

#include <unity/unity.h>

#include "dataq.h"
#include "netio.h"
#include "vtaskmgr.h"

static endpoint_t* g_ep1;
static endpoint_t* g_ep2;
static int         g_ep1_checks;

static vtask_t* make_io_task(endpoint_t* ep)
{
    vtask_t*      t = (vtask_t*)calloc(1, sizeof(*t));
    vtask_data_t* d = (vtask_data_t*)calloc(1, sizeof(*d));

    TEST_ASSERT_NOT_NULL(t);
    TEST_ASSERT_NOT_NULL(d);
    d->vtype       = VTASK_IO;
    d->u.iodata.ep = ep;
    t->data        = d;
    return t;
}

static vtask_t* make_generic_task(void)
{
    vtask_t*      t = (vtask_t*)calloc(1, sizeof(*t));
    vtask_data_t* d = (vtask_data_t*)calloc(1, sizeof(*d));

    TEST_ASSERT_NOT_NULL(t);
    TEST_ASSERT_NOT_NULL(d);
    d->vtype = VTASK_GENERIC;
    t->data  = d;
    return t;
}

static void free_task(vtask_t* t)
{
    if (t != NULL) {
        free(t->data);
        free(t);
    }
}

/* ep1 is busy on the first check of this scan, then its running task
 * finishes and it is free for every later check -- the live interleaving */
static int ep1_unblocks_mid_scan(endpoint_t* ep)
{
    if (ep == g_ep1) {
        return (g_ep1_checks++ == 0);
    }
    return 0;
}

static int ep1_busy(endpoint_t* ep) { return (ep == g_ep1); }
static int none_busy(endpoint_t* ep) { (void)ep; return 0; }

static void order_setup(dataq_t* q)
{
    dataq_init(q, NULL);
    g_ep1        = (endpoint_t*)calloc(1, sizeof(endpoint_t));
    g_ep2        = (endpoint_t*)calloc(1, sizeof(endpoint_t));
    g_ep1_checks = 0;
}

static void order_teardown(dataq_t* q)
{
    data_item_t* it;

    while ((it = dataq_deq(q, NULL)) != NULL) {
        free_task(ITPTR_TO_VTASK(it));
    }
    free(g_ep1);
    free(g_ep2);
}

/* the bug: a later message must never overtake an earlier one of the same
 * endpoint, even if the endpoint frees up while the scan is between them */
static void test_later_task_of_skipped_endpoint_is_not_dequeued(void)
{
    dataq_t  q;
    vtask_t* first;
    vtask_t* second;
    vtask_t* got;

    order_setup(&q);
    first  = make_io_task(g_ep1);
    second = make_io_task(g_ep1);
    dataq_enq(&q, &(first->link));
    dataq_enq(&q, &(second->link));

    got = vtask_deq_eligible(&q, ep1_unblocks_mid_scan);
    TEST_ASSERT_NULL_MESSAGE(got,
        "task N was skipped as busy, so task N+1 of the same endpoint must "
        "not be dequeued ahead of it in the same scan");

    /* next scan: the endpoint is free, and N comes out first */
    got = vtask_deq_eligible(&q, none_busy);
    TEST_ASSERT_EQUAL_PTR(first, got);
    free_task(got);
    got = vtask_deq_eligible(&q, none_busy);
    TEST_ASSERT_EQUAL_PTR(second, got);
    free_task(got);

    order_teardown(&q);
}

/* a busy endpoint must not hold up other endpoints' tasks */
static void test_other_endpoint_still_dispatched(void)
{
    dataq_t  q;
    vtask_t* a = NULL;
    vtask_t* c = NULL;
    vtask_t* got;

    order_setup(&q);
    a = make_io_task(g_ep1);
    c = make_io_task(g_ep2);
    dataq_enq(&q, &(a->link));
    dataq_enq(&q, &(c->link));

    got = vtask_deq_eligible(&q, ep1_busy);
    TEST_ASSERT_EQUAL_PTR(c, got);
    free_task(got);

    order_teardown(&q);
}

/* FIFO when nothing is busy; non-IO tasks are always dispatchable */
static void test_fifo_and_generic_tasks(void)
{
    dataq_t  q;
    vtask_t* a;
    vtask_t* b;
    vtask_t* g;
    vtask_t* got;

    order_setup(&q);
    a = make_io_task(g_ep1);
    b = make_io_task(g_ep1);
    dataq_enq(&q, &(a->link));
    dataq_enq(&q, &(b->link));
    got = vtask_deq_eligible(&q, none_busy);
    TEST_ASSERT_EQUAL_PTR(a, got);
    free_task(got);
    order_teardown(&q);

    order_setup(&q);
    a = make_io_task(g_ep1);
    g = make_generic_task();
    dataq_enq(&q, &(a->link));
    dataq_enq(&q, &(g->link));
    got = vtask_deq_eligible(&q, ep1_busy);
    TEST_ASSERT_EQUAL_PTR(g, got);
    free_task(got);
    order_teardown(&q);
}

void test_vtask_order(void)
{
    RUN_TEST(test_later_task_of_skipped_endpoint_is_not_dequeued);
    RUN_TEST(test_other_endpoint_still_dispatched);
    RUN_TEST(test_fifo_and_generic_tasks);
}