#include <errno.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>

#include <unity/unity.h>

#include "../raft/raft.h"

/* ---------- stub callbacks ---------- */

static int stub_send_vote_request(void *ctx, int peer_idx, uint64_t term)
{
    (void)ctx; (void)peer_idx; (void)term;
    return 0;
}

static void stub_become_leader(void *ctx, uint64_t term)
{
    (void)ctx; (void)term;
}

static void stub_become_follower(void *ctx, uint64_t term, int leader_idx)
{
    (void)ctx; (void)term; (void)leader_idx;
}

static int stub_persist(void *ctx, uint64_t term, int voted_for)
{
    (void)ctx; (void)term; (void)voted_for;
    return 0;
}

static void stub_schedule_timeout(void *ctx, uint32_t delay_ms)
{
    (void)ctx; (void)delay_ms;
}

static void stub_cancel_timeout(void *ctx)
{
    (void)ctx;
}

static void stub_start_election_after_delay(void *ctx, uint32_t delay_ms)
{
    (void)ctx; (void)delay_ms;
}

/* Build a fully-populated callbacks struct */
static raft_callbacks_t make_full_cbs(void)
{
    raft_callbacks_t cbs;
    memset(&cbs, 0, sizeof(cbs));
    cbs.on_send_vote_request         = stub_send_vote_request;
    cbs.on_become_leader             = stub_become_leader;
    cbs.on_become_follower           = stub_become_follower;
    cbs.on_persist                   = stub_persist;
    cbs.on_schedule_timeout          = stub_schedule_timeout;
    cbs.on_cancel_timeout            = stub_cancel_timeout;
    cbs.on_start_election_after_delay = stub_start_election_after_delay;
    /* on_vote_eligible and on_trace left NULL (optional) */
    return cbs;
}

/* ---------- mock infrastructure for raft_start_election tests ---------- */

/* Per-test counters — reset by each test before calling start_election */
typedef struct {
    int      send_vote_request_count;
    int      last_send_peer_idx;
    uint64_t last_send_term;
    /* track each peer index sent (up to 8 for test purposes) */
    int      sent_peers[8];

    int      schedule_timeout_count;
    uint32_t last_schedule_delay;

    int      persist_count;
    uint64_t last_persist_term;
    int      last_persist_voted_for;
    int      persist_return_value;   /* configurable: 0=success, non-zero=fail */

    int      become_leader_count;
    uint64_t last_become_leader_term;

    /* on_vote_eligible mock */
    int      vote_eligible_return_value; /* configurable: 1=grant, 0=deny; default 1 */
    int      vote_eligible_call_count;

    /* on_trace mock */
    int      trace_call_count;
    char     last_trace_event[64];
} mock_cbs_state_t;

static mock_cbs_state_t g_mock;

static void reset_mock(void)
{
    memset(&g_mock, 0, sizeof(g_mock));
    /* Defaults: persist succeeds, vote_eligible grants */
    g_mock.persist_return_value      = 0;
    g_mock.vote_eligible_return_value = 1;
}

static int mock_send_vote_request(void *ctx, int peer_idx, uint64_t term)
{
    (void)ctx;
    if (g_mock.send_vote_request_count < 8)
        g_mock.sent_peers[g_mock.send_vote_request_count] = peer_idx;
    g_mock.last_send_peer_idx = peer_idx;
    g_mock.last_send_term     = term;
    g_mock.send_vote_request_count++;
    return 0;
}

static void mock_become_leader(void *ctx, uint64_t term)
{
    (void)ctx;
    g_mock.become_leader_count++;
    g_mock.last_become_leader_term = term;
}

static int mock_persist(void *ctx, uint64_t term, int voted_for)
{
    (void)ctx;
    g_mock.persist_count++;
    g_mock.last_persist_term      = term;
    g_mock.last_persist_voted_for = voted_for;
    return g_mock.persist_return_value;
}

static void mock_schedule_timeout(void *ctx, uint32_t delay_ms)
{
    (void)ctx;
    g_mock.schedule_timeout_count++;
    g_mock.last_schedule_delay = delay_ms;
}

static int mock_vote_eligible(void *ctx, int from_idx, uint64_t term)
{
    (void)ctx; (void)from_idx; (void)term;
    g_mock.vote_eligible_call_count++;
    return g_mock.vote_eligible_return_value;
}

static void mock_trace(void *ctx, const char *event, const char *detail)
{
    (void)ctx; (void)detail;
    g_mock.trace_call_count++;
    if (event) {
        strncpy(g_mock.last_trace_event, event,
                sizeof(g_mock.last_trace_event) - 1);
        g_mock.last_trace_event[sizeof(g_mock.last_trace_event) - 1] = '\0';
    }
}

/* Build callbacks that record invocations in g_mock */
static raft_callbacks_t make_mock_cbs(void)
{
    raft_callbacks_t cbs;
    memset(&cbs, 0, sizeof(cbs));
    cbs.on_send_vote_request         = mock_send_vote_request;
    cbs.on_become_leader             = mock_become_leader;
    cbs.on_become_follower           = stub_become_follower;  /* plain stub */
    cbs.on_persist                   = mock_persist;
    cbs.on_schedule_timeout          = mock_schedule_timeout;
    cbs.on_cancel_timeout            = stub_cancel_timeout;
    cbs.on_start_election_after_delay = stub_start_election_after_delay;
    /* on_vote_eligible and on_trace left NULL — tests that need them set explicitly */
    return cbs;
}

/* ---------- helpers ---------- */

/* Initialize a raft_state_t with mock callbacks; n_peers and self_idx configurable */
static int init_node(raft_state_t *s, raft_callbacks_t *cbs, int n_peers, int self_idx)
{
    raft_config_t cfg;
    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers             = n_peers;
    cfg.self_idx            = self_idx;
    cfg.election_timeout_ms = 1000;
    cfg.cbs                 = cbs;
    return raft_init(s, &cfg);
}

/* ---------- raft_init tests ---------- */

/* raft_init with NULL required callback returns -EINVAL and does not modify s */
static void test_raft_init_null_send_vote_request_returns_einval(void)
{
    raft_state_t    s;
    raft_callbacks_t cbs = make_full_cbs();
    raft_config_t   cfg;

    /* canary: fill s with a non-zero sentinel so we can verify it's untouched */
    memset(&s, 0xAB, sizeof(s));

    cbs.on_send_vote_request = NULL; /* knock out a required callback */

    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers   = 3;
    cfg.self_idx  = 0;
    cfg.cbs       = &cbs;
    cfg.ctx       = NULL;

    int rc = raft_init(&s, &cfg);
    TEST_ASSERT_EQUAL_INT(-EINVAL, rc);

    /* s must be completely unchanged (canary check — spot-check first byte) */
    {
        unsigned char buf[sizeof(s)];
        memset(buf, 0xAB, sizeof(buf));
        TEST_ASSERT_EQUAL_MEMORY(buf, &s, sizeof(s));
    }
}

static void test_raft_init_null_become_leader_returns_einval(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_full_cbs();
    raft_config_t    cfg;

    memset(&s, 0, sizeof(s));
    cbs.on_become_leader = NULL;

    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers = 2; cfg.self_idx = 0; cfg.cbs = &cbs;

    TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
}

static void test_raft_init_null_become_follower_returns_einval(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_full_cbs();
    raft_config_t    cfg;

    memset(&s, 0, sizeof(s));
    cbs.on_become_follower = NULL;

    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers = 2; cfg.self_idx = 0; cfg.cbs = &cbs;

    TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
}

static void test_raft_init_null_persist_returns_einval(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_full_cbs();
    raft_config_t    cfg;

    memset(&s, 0, sizeof(s));
    cbs.on_persist = NULL;

    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers = 2; cfg.self_idx = 0; cfg.cbs = &cbs;

    TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
}

static void test_raft_init_null_schedule_timeout_returns_einval(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_full_cbs();
    raft_config_t    cfg;

    memset(&s, 0, sizeof(s));
    cbs.on_schedule_timeout = NULL;

    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers = 2; cfg.self_idx = 0; cfg.cbs = &cbs;

    TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
}

static void test_raft_init_null_cancel_timeout_returns_einval(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_full_cbs();
    raft_config_t    cfg;

    memset(&s, 0, sizeof(s));
    cbs.on_cancel_timeout = NULL;

    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers = 2; cfg.self_idx = 0; cfg.cbs = &cbs;

    TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
}

static void test_raft_init_null_start_election_after_delay_returns_einval(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_full_cbs();
    raft_config_t    cfg;

    memset(&s, 0, sizeof(s));
    cbs.on_start_election_after_delay = NULL;

    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers = 2; cfg.self_idx = 0; cfg.cbs = &cbs;

    TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));
}

/* n_peers == 0 → -EINVAL */
static void test_raft_init_zero_peers_returns_einval(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_full_cbs();
    raft_config_t    cfg;

    memset(&s, 0xAB, sizeof(s));
    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers  = 0;
    cfg.self_idx = 0;
    cfg.cbs      = &cbs;

    TEST_ASSERT_EQUAL_INT(-EINVAL, raft_init(&s, &cfg));

    /* s must be unchanged */
    unsigned char buf[sizeof(s)];
    memset(buf, 0xAB, sizeof(buf));
    TEST_ASSERT_EQUAL_MEMORY(buf, &s, sizeof(s));
}

/* Successful init: check all fields */
static void test_raft_init_success_fields(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_full_cbs();
    raft_config_t    cfg;

    memset(&s, 0, sizeof(s));
    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers              = 3;
    cfg.self_idx             = 1;
    cfg.election_timeout_ms  = 1500;
    cfg.my_priority          = 2;
    cfg.initial_term         = 7;
    cfg.initial_voted_for    = -1;
    cfg.cbs                  = &cbs;
    cfg.ctx                  = (void *)0xDEADBEEF;

    int rc = raft_init(&s, &cfg);
    TEST_ASSERT_EQUAL_INT(0, rc);

    TEST_ASSERT_EQUAL_INT(RAFT_FOLLOWER, s.role);
    TEST_ASSERT_EQUAL_INT(3, s.n_peers);
    TEST_ASSERT_EQUAL_INT(1, s.self_idx);
    TEST_ASSERT_EQUAL_UINT32(1500, s.election_timeout_ms);
    TEST_ASSERT_EQUAL_INT(2, s.my_priority);
    TEST_ASSERT_EQUAL_UINT64(7, s.term);
    TEST_ASSERT_EQUAL_INT(-1, s.voted_for);
    TEST_ASSERT_EQUAL_UINT64(0, s.voted_for_term);
    TEST_ASSERT_EQUAL_INT(0, s.votes_granted);
    TEST_ASSERT_EQUAL_INT(0, s.replies_received);
    TEST_ASSERT_EQUAL_INT(0, s.election_decided);

    /* cbs/ctx must be stored in raft_state_t for the state machine to fire callbacks */
    TEST_ASSERT_EQUAL_PTR(&cbs, s.cbs);
    TEST_ASSERT_EQUAL_PTR((void *)0xDEADBEEF, s.ctx);
}

/* election_timeout_ms == 0 → default 2000 */
static void test_raft_init_default_election_timeout(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_full_cbs();
    raft_config_t    cfg;

    memset(&s, 0, sizeof(s));
    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers             = 3;
    cfg.self_idx            = 0;
    cfg.election_timeout_ms = 0; /* trigger default */
    cfg.cbs                 = &cbs;

    int rc = raft_init(&s, &cfg);
    TEST_ASSERT_EQUAL_INT(0, rc);
    TEST_ASSERT_EQUAL_UINT32(2000, s.election_timeout_ms);
}

/* optional callbacks (on_vote_eligible, on_trace) may be NULL — must succeed */
static void test_raft_init_optional_callbacks_null_succeeds(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_full_cbs();
    raft_config_t    cfg;

    memset(&s, 0, sizeof(s));
    cbs.on_vote_eligible = NULL;
    cbs.on_trace         = NULL;

    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers  = 3;
    cfg.self_idx = 0;
    cfg.cbs      = &cbs;

    TEST_ASSERT_EQUAL_INT(0, raft_init(&s, &cfg));
    TEST_ASSERT_EQUAL_INT(RAFT_FOLLOWER, s.role);
}

/* ---------- raft_start_election tests (task 3.2) ---------- */

/*
 * test_start_election_from_follower_3node
 *
 * 3-node cluster (self=0).  raft_start_election transitions to CANDIDATE,
 * increments term, records self-vote, fires on_persist(new_term, self_idx),
 * fires on_send_vote_request for each peer != self_idx (peers 1 and 2),
 * fires on_schedule_timeout once, returns RAFT_OK.
 */
static void test_start_election_from_follower_3node(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();

    reset_mock();
    TEST_ASSERT_EQUAL_INT(0, init_node(&s, &cbs, 3, 0));
    TEST_ASSERT_EQUAL_INT(RAFT_FOLLOWER, s.role);
    TEST_ASSERT_EQUAL_UINT64(0, s.term);

    int rc = raft_start_election(&s);

    TEST_ASSERT_EQUAL_INT(RAFT_OK, rc);
    TEST_ASSERT_EQUAL_INT(RAFT_CANDIDATE, s.role);
    TEST_ASSERT_EQUAL_UINT64(1, s.term);
    TEST_ASSERT_EQUAL_INT(0, s.self_idx);
    TEST_ASSERT_EQUAL_INT(0, s.voted_for);          /* voted_for == self_idx */
    TEST_ASSERT_EQUAL_UINT64(1, s.voted_for_term);  /* voted_for_term == new term */
    TEST_ASSERT_EQUAL_INT(1, s.votes_granted);       /* self-vote counted */
    TEST_ASSERT_EQUAL_INT(0, s.replies_received);
    TEST_ASSERT_EQUAL_INT(0, s.election_decided);

    /* on_persist must fire once with (new_term=1, self_idx=0) */
    TEST_ASSERT_EQUAL_INT(1, g_mock.persist_count);
    TEST_ASSERT_EQUAL_UINT64(1, g_mock.last_persist_term);
    TEST_ASSERT_EQUAL_INT(0, g_mock.last_persist_voted_for);

    /* on_send_vote_request must fire for peers 1 and 2 (not self=0) */
    TEST_ASSERT_EQUAL_INT(2, g_mock.send_vote_request_count);
    /* Both sends must use the new term */
    TEST_ASSERT_EQUAL_UINT64(1, g_mock.last_send_term);
    /* Verify neither sent peer is self_idx=0 */
    {
        int i;
        for (i = 0; i < g_mock.send_vote_request_count; i++) {
            TEST_ASSERT_NOT_EQUAL(0, g_mock.sent_peers[i]);
        }
    }

    /* on_schedule_timeout must fire exactly once */
    TEST_ASSERT_EQUAL_INT(1, g_mock.schedule_timeout_count);
    TEST_ASSERT_EQUAL_UINT32(1000, g_mock.last_schedule_delay);

    /* on_become_leader must NOT fire (multi-node path) */
    TEST_ASSERT_EQUAL_INT(0, g_mock.become_leader_count);
}

/*
 * test_start_election_single_node
 *
 * 1-node cluster (self=0).  raft_start_election shortcircuits to LEADER,
 * fires on_persist then on_become_leader, returns RAFT_ELECTED_IMMEDIATELY.
 * No on_send_vote_request or on_schedule_timeout calls.
 */
static void test_start_election_single_node(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();

    reset_mock();
    TEST_ASSERT_EQUAL_INT(0, init_node(&s, &cbs, 1, 0));

    int rc = raft_start_election(&s);

    TEST_ASSERT_EQUAL_INT(RAFT_ELECTED_IMMEDIATELY, rc);
    TEST_ASSERT_EQUAL_INT(RAFT_LEADER, s.role);
    TEST_ASSERT_EQUAL_UINT64(1, s.term);
    TEST_ASSERT_EQUAL_INT(0, s.voted_for);          /* self-vote */
    TEST_ASSERT_EQUAL_INT(1, s.election_decided);

    /* on_persist fires once with (term=1, self_idx=0) */
    TEST_ASSERT_EQUAL_INT(1, g_mock.persist_count);
    TEST_ASSERT_EQUAL_UINT64(1, g_mock.last_persist_term);
    TEST_ASSERT_EQUAL_INT(0, g_mock.last_persist_voted_for);

    /* on_become_leader fires once with term=1 */
    TEST_ASSERT_EQUAL_INT(1, g_mock.become_leader_count);
    TEST_ASSERT_EQUAL_UINT64(1, g_mock.last_become_leader_term);

    /* on_send_vote_request must NOT fire */
    TEST_ASSERT_EQUAL_INT(0, g_mock.send_vote_request_count);

    /* on_schedule_timeout must NOT fire */
    TEST_ASSERT_EQUAL_INT(0, g_mock.schedule_timeout_count);
}

/*
 * test_start_election_already_candidate
 *
 * Call raft_start_election once (become CANDIDATE), then call again.
 * Second call must return -EALREADY and leave state completely unchanged.
 */
static void test_start_election_already_candidate(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();

    reset_mock();
    TEST_ASSERT_EQUAL_INT(0, init_node(&s, &cbs, 3, 1));

    /* First election — becomes CANDIDATE */
    TEST_ASSERT_EQUAL_INT(RAFT_OK, raft_start_election(&s));
    TEST_ASSERT_EQUAL_INT(RAFT_CANDIDATE, s.role);
    uint64_t term_after_first = s.term;

    /* Snapshot the state before the second call */
    int     saved_voted_for      = s.voted_for;
    int     saved_votes_granted  = s.votes_granted;
    int     saved_replies_recvd  = s.replies_received;
    int     saved_election_dec   = s.election_decided;

    reset_mock();

    /* Second call must be rejected */
    int rc = raft_start_election(&s);
    TEST_ASSERT_EQUAL_INT(-EALREADY, rc);

    /* State must be unchanged */
    TEST_ASSERT_EQUAL_INT(RAFT_CANDIDATE, s.role);
    TEST_ASSERT_EQUAL_UINT64(term_after_first, s.term);
    TEST_ASSERT_EQUAL_INT(saved_voted_for,     s.voted_for);
    TEST_ASSERT_EQUAL_INT(saved_votes_granted, s.votes_granted);
    TEST_ASSERT_EQUAL_INT(saved_replies_recvd, s.replies_received);
    TEST_ASSERT_EQUAL_INT(saved_election_dec,  s.election_decided);

    /* No callbacks must have fired on the second call */
    TEST_ASSERT_EQUAL_INT(0, g_mock.persist_count);
    TEST_ASSERT_EQUAL_INT(0, g_mock.send_vote_request_count);
    TEST_ASSERT_EQUAL_INT(0, g_mock.schedule_timeout_count);
    TEST_ASSERT_EQUAL_INT(0, g_mock.become_leader_count);
}

/*
 * test_start_election_already_leader
 *
 * Manually set role=RAFT_LEADER, then call raft_start_election.
 * Must return -EALREADY without modifying any state or firing any callback.
 */
static void test_start_election_already_leader(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();

    reset_mock();
    TEST_ASSERT_EQUAL_INT(0, init_node(&s, &cbs, 3, 2));

    /* Manually elevate to LEADER */
    s.role = RAFT_LEADER;
    s.term = 5;

    int rc = raft_start_election(&s);
    TEST_ASSERT_EQUAL_INT(-EALREADY, rc);

    /* All state must be unchanged */
    TEST_ASSERT_EQUAL_INT(RAFT_LEADER, s.role);
    TEST_ASSERT_EQUAL_UINT64(5, s.term);

    /* No callbacks must fire */
    TEST_ASSERT_EQUAL_INT(0, g_mock.persist_count);
    TEST_ASSERT_EQUAL_INT(0, g_mock.send_vote_request_count);
    TEST_ASSERT_EQUAL_INT(0, g_mock.schedule_timeout_count);
    TEST_ASSERT_EQUAL_INT(0, g_mock.become_leader_count);
}

/* ---------- raft_on_vote_request tests (task 3.3) ---------- */

/*
 * Helper: init a 3-node node with mock callbacks (including trace).
 * term, role, voted_for can be set after init.
 */
static int init_vote_node(raft_state_t *s, raft_callbacks_t *cbs,
                          int n_peers, int self_idx, uint64_t initial_term)
{
    raft_config_t cfg;
    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers             = n_peers;
    cfg.self_idx            = self_idx;
    cfg.election_timeout_ms = 1000;
    cfg.initial_term        = initial_term;
    cfg.initial_voted_for   = -1;
    cfg.cbs                 = cbs;
    return raft_init(s, &cfg);
}

/*
 * test_vote_req_stale_term
 *
 * Node at term=5, receives request with term=3.
 * Expected: RAFT_DENY, *reply_term=5, state unchanged,
 *           on_trace fired with "vote_denied_stale_term".
 */
static void test_vote_req_stale_term(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();
    uint64_t         reply_term = 0;

    cbs.on_trace = mock_trace;
    reset_mock();

    TEST_ASSERT_EQUAL_INT(0, init_vote_node(&s, &cbs, 3, 0, 5));
    /* Confirm starting state */
    TEST_ASSERT_EQUAL_UINT64(5, s.term);
    TEST_ASSERT_EQUAL_INT(RAFT_FOLLOWER, s.role);
    TEST_ASSERT_EQUAL_INT(-1, s.voted_for);

    int rc = raft_on_vote_request(&s, 1, 3, &reply_term);

    TEST_ASSERT_EQUAL_INT(RAFT_DENY, rc);
    TEST_ASSERT_EQUAL_UINT64(5, reply_term);

    /* State must be unchanged */
    TEST_ASSERT_EQUAL_UINT64(5, s.term);
    TEST_ASSERT_EQUAL_INT(RAFT_FOLLOWER, s.role);
    TEST_ASSERT_EQUAL_INT(-1, s.voted_for);

    /* on_trace must fire with "vote_denied_stale_term" */
    TEST_ASSERT_GREATER_THAN_INT(0, g_mock.trace_call_count);
    TEST_ASSERT_EQUAL_STRING("vote_denied_stale_term", g_mock.last_trace_event);

    /* on_persist must NOT fire */
    TEST_ASSERT_EQUAL_INT(0, g_mock.persist_count);
}

/*
 * test_vote_req_higher_term_updates_state
 *
 * Node at term=2, receives request with term=5 (higher).
 * Expected: s->term updated to 5, voted_for cleared to -1, role=FOLLOWER.
 * Since voted_for is unset and persist succeeds: RAFT_GRANT.
 * reply_term = 5.
 */
static void test_vote_req_higher_term_updates_state(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();
    uint64_t         reply_term = 0;

    cbs.on_trace = mock_trace;
    reset_mock();

    TEST_ASSERT_EQUAL_INT(0, init_vote_node(&s, &cbs, 3, 0, 2));
    /* Simulate node was CANDIDATE in term=2 */
    s.role       = RAFT_CANDIDATE;
    s.voted_for  = 0;   /* voted for self */
    s.voted_for_term = 2;

    int rc = raft_on_vote_request(&s, 1, 5, &reply_term);

    /* Term upgrade must happen: term updated, role stepped down */
    TEST_ASSERT_EQUAL_UINT64(5, s.term);
    TEST_ASSERT_EQUAL_INT(RAFT_FOLLOWER, s.role);

    /* Then grant because voted_for is cleared and persist succeeds */
    TEST_ASSERT_EQUAL_INT(RAFT_GRANT, rc);
    TEST_ASSERT_EQUAL_UINT64(5, reply_term);

    /* on_persist must fire once */
    TEST_ASSERT_EQUAL_INT(1, g_mock.persist_count);
    TEST_ASSERT_EQUAL_UINT64(5, g_mock.last_persist_term);
    TEST_ASSERT_EQUAL_INT(1, g_mock.last_persist_voted_for);

    /* voted_for set on grant */
    TEST_ASSERT_EQUAL_INT(1, s.voted_for);
    TEST_ASSERT_EQUAL_UINT64(5, s.voted_for_term);
}

/*
 * test_vote_req_same_term_already_voted_different
 *
 * Node at term=5, voted_for=1, voted_for_term=5.
 * Receives request from idx=2 at term=5.
 * Expected: RAFT_DENY, "vote_denied_already_voted" trace.
 */
static void test_vote_req_same_term_already_voted_different(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();
    uint64_t         reply_term = 0;

    cbs.on_trace = mock_trace;
    reset_mock();

    TEST_ASSERT_EQUAL_INT(0, init_vote_node(&s, &cbs, 3, 0, 5));
    s.voted_for      = 1;
    s.voted_for_term = 5;

    int rc = raft_on_vote_request(&s, 2, 5, &reply_term);

    TEST_ASSERT_EQUAL_INT(RAFT_DENY, rc);
    TEST_ASSERT_EQUAL_UINT64(5, reply_term);

    /* State: voted_for still 1 (not 2), term unchanged */
    TEST_ASSERT_EQUAL_INT(1, s.voted_for);
    TEST_ASSERT_EQUAL_UINT64(5, s.term);

    /* on_trace fires with already_voted */
    TEST_ASSERT_GREATER_THAN_INT(0, g_mock.trace_call_count);
    TEST_ASSERT_EQUAL_STRING("vote_denied_already_voted", g_mock.last_trace_event);

    /* on_persist must NOT fire */
    TEST_ASSERT_EQUAL_INT(0, g_mock.persist_count);
}

/*
 * test_vote_req_same_term_idempotent_same_candidate
 *
 * Node at term=5, voted_for=1, voted_for_term=5.
 * Receives request from idx=1 at term=5 (same candidate, same term).
 * Expected: idempotent re-grant → RAFT_GRANT, voted_for still 1.
 */
static void test_vote_req_same_term_idempotent_same_candidate(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();
    uint64_t         reply_term = 0;

    cbs.on_trace = mock_trace;
    reset_mock();

    TEST_ASSERT_EQUAL_INT(0, init_vote_node(&s, &cbs, 3, 0, 5));
    s.voted_for      = 1;
    s.voted_for_term = 5;

    int rc = raft_on_vote_request(&s, 1, 5, &reply_term);

    TEST_ASSERT_EQUAL_INT(RAFT_GRANT, rc);
    TEST_ASSERT_EQUAL_UINT64(5, reply_term);

    /* voted_for still 1 */
    TEST_ASSERT_EQUAL_INT(1, s.voted_for);
    TEST_ASSERT_EQUAL_UINT64(5, s.voted_for_term);

    /* on_persist must fire once for the re-grant */
    TEST_ASSERT_EQUAL_INT(1, g_mock.persist_count);
}

/*
 * test_vote_req_leader_denies
 *
 * Node is RAFT_LEADER at term=5, receives request at term=5 (same term, no upgrade).
 * Expected: RAFT_DENY ("vote_denied_role" trace), role stays LEADER.
 */
static void test_vote_req_leader_denies(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();
    uint64_t         reply_term = 0;

    cbs.on_trace = mock_trace;
    reset_mock();

    TEST_ASSERT_EQUAL_INT(0, init_vote_node(&s, &cbs, 3, 0, 5));
    s.role = RAFT_LEADER;

    int rc = raft_on_vote_request(&s, 1, 5, &reply_term);

    TEST_ASSERT_EQUAL_INT(RAFT_DENY, rc);
    TEST_ASSERT_EQUAL_UINT64(5, reply_term);

    /* Role gate fires: still LEADER (term==request term, no upgrade) */
    TEST_ASSERT_EQUAL_INT(RAFT_LEADER, s.role);

    /* on_trace fires with "vote_denied_role" */
    TEST_ASSERT_GREATER_THAN_INT(0, g_mock.trace_call_count);
    TEST_ASSERT_EQUAL_STRING("vote_denied_role", g_mock.last_trace_event);

    /* on_persist must NOT fire */
    TEST_ASSERT_EQUAL_INT(0, g_mock.persist_count);
}

/*
 * test_vote_req_on_vote_eligible_denies
 *
 * on_vote_eligible returns 0 → RAFT_DENY, voted_for unchanged,
 * "vote_denied_freshness" trace fires.
 */
static void test_vote_req_on_vote_eligible_denies(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();
    uint64_t         reply_term = 0;

    cbs.on_vote_eligible = mock_vote_eligible;
    cbs.on_trace         = mock_trace;
    reset_mock();
    g_mock.vote_eligible_return_value = 0; /* deny */

    TEST_ASSERT_EQUAL_INT(0, init_vote_node(&s, &cbs, 3, 0, 5));

    int rc = raft_on_vote_request(&s, 1, 5, &reply_term);

    TEST_ASSERT_EQUAL_INT(RAFT_DENY, rc);
    TEST_ASSERT_EQUAL_UINT64(5, reply_term);

    /* voted_for must be unchanged */
    TEST_ASSERT_EQUAL_INT(-1, s.voted_for);

    /* on_vote_eligible must have been called */
    TEST_ASSERT_EQUAL_INT(1, g_mock.vote_eligible_call_count);

    /* on_trace fires with "vote_denied_freshness" */
    TEST_ASSERT_GREATER_THAN_INT(0, g_mock.trace_call_count);
    TEST_ASSERT_EQUAL_STRING("vote_denied_freshness", g_mock.last_trace_event);

    /* on_persist must NOT fire */
    TEST_ASSERT_EQUAL_INT(0, g_mock.persist_count);
}

/*
 * test_vote_req_on_vote_eligible_grants
 *
 * on_vote_eligible returns 1 and persist succeeds → RAFT_GRANT, voted_for set.
 */
static void test_vote_req_on_vote_eligible_grants(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();
    uint64_t         reply_term = 0;

    cbs.on_vote_eligible = mock_vote_eligible;
    cbs.on_trace         = mock_trace;
    reset_mock();
    g_mock.vote_eligible_return_value = 1; /* grant */

    TEST_ASSERT_EQUAL_INT(0, init_vote_node(&s, &cbs, 3, 0, 5));

    int rc = raft_on_vote_request(&s, 1, 5, &reply_term);

    TEST_ASSERT_EQUAL_INT(RAFT_GRANT, rc);
    TEST_ASSERT_EQUAL_UINT64(5, reply_term);

    /* voted_for must be set */
    TEST_ASSERT_EQUAL_INT(1, s.voted_for);
    TEST_ASSERT_EQUAL_UINT64(5, s.voted_for_term);

    /* on_vote_eligible called once */
    TEST_ASSERT_EQUAL_INT(1, g_mock.vote_eligible_call_count);

    /* on_persist called once */
    TEST_ASSERT_EQUAL_INT(1, g_mock.persist_count);

    /* on_trace fires "vote_granted" */
    TEST_ASSERT_GREATER_THAN_INT(0, g_mock.trace_call_count);
    TEST_ASSERT_EQUAL_STRING("vote_granted", g_mock.last_trace_event);
}

/*
 * test_vote_req_on_vote_eligible_null
 *
 * on_vote_eligible is NULL → treated as eligible, grant if persist ok.
 */
static void test_vote_req_on_vote_eligible_null(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();
    uint64_t         reply_term = 0;

    /* on_vote_eligible left NULL in make_mock_cbs */
    cbs.on_trace = mock_trace;
    reset_mock();

    TEST_ASSERT_EQUAL_INT(0, init_vote_node(&s, &cbs, 3, 0, 5));

    int rc = raft_on_vote_request(&s, 1, 5, &reply_term);

    TEST_ASSERT_EQUAL_INT(RAFT_GRANT, rc);
    TEST_ASSERT_EQUAL_UINT64(5, reply_term);

    /* voted_for must be set */
    TEST_ASSERT_EQUAL_INT(1, s.voted_for);
    TEST_ASSERT_EQUAL_UINT64(5, s.voted_for_term);

    /* on_persist called once */
    TEST_ASSERT_EQUAL_INT(1, g_mock.persist_count);
}

/*
 * test_vote_req_persist_fails
 *
 * on_persist returns non-zero → RAFT_DENY, voted_for unchanged.
 */
static void test_vote_req_persist_fails(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();
    uint64_t         reply_term = 0;

    cbs.on_trace = mock_trace;
    reset_mock();
    g_mock.persist_return_value = -1; /* fail */

    TEST_ASSERT_EQUAL_INT(0, init_vote_node(&s, &cbs, 3, 0, 5));

    int rc = raft_on_vote_request(&s, 1, 5, &reply_term);

    TEST_ASSERT_EQUAL_INT(RAFT_DENY, rc);
    TEST_ASSERT_EQUAL_UINT64(5, reply_term);

    /* voted_for must NOT be updated */
    TEST_ASSERT_EQUAL_INT(-1, s.voted_for);
    TEST_ASSERT_EQUAL_UINT64(0, s.voted_for_term);

    /* on_persist called once (it ran, but failed) */
    TEST_ASSERT_EQUAL_INT(1, g_mock.persist_count);
}

/*
 * test_vote_req_reply_term_always_set
 *
 * Verify that *reply_term == s->term on every return path by testing
 * several scenarios and checking reply_term each time.
 */
static void test_vote_req_reply_term_always_set(void)
{
    raft_state_t     s;
    raft_callbacks_t cbs = make_mock_cbs();
    uint64_t         reply_term;

    /* Path 1: stale term deny */
    reset_mock();
    TEST_ASSERT_EQUAL_INT(0, init_vote_node(&s, &cbs, 3, 0, 7));
    reply_term = 0;
    raft_on_vote_request(&s, 1, 3, &reply_term);
    TEST_ASSERT_EQUAL_UINT64(s.term, reply_term); /* must equal current term=7 */

    /* Path 2: term upgrade + grant */
    reset_mock();
    TEST_ASSERT_EQUAL_INT(0, init_vote_node(&s, &cbs, 3, 0, 3));
    reply_term = 0;
    raft_on_vote_request(&s, 1, 7, &reply_term);
    TEST_ASSERT_EQUAL_UINT64(s.term, reply_term); /* must equal upgraded term=7 */

    /* Path 3: already voted for different — deny */
    reset_mock();
    TEST_ASSERT_EQUAL_INT(0, init_vote_node(&s, &cbs, 3, 0, 5));
    s.voted_for = 1; s.voted_for_term = 5;
    reply_term = 0;
    raft_on_vote_request(&s, 2, 5, &reply_term);
    TEST_ASSERT_EQUAL_UINT64(s.term, reply_term); /* must equal 5 */

    /* Path 4: persist fails — deny */
    g_mock.persist_return_value = -1;
    reset_mock();
    g_mock.persist_return_value = -1;
    TEST_ASSERT_EQUAL_INT(0, init_vote_node(&s, &cbs, 3, 0, 5));
    reply_term = 0;
    raft_on_vote_request(&s, 1, 5, &reply_term);
    TEST_ASSERT_EQUAL_UINT64(s.term, reply_term); /* must equal 5 */
}

/* ---------- raft_snapshot tests ---------- */

static void test_raft_snapshot_returns_current_state(void)
{
    raft_state_t    s;
    raft_snapshot_t snap;
    raft_callbacks_t cbs = make_full_cbs();
    raft_config_t   cfg;

    memset(&s, 0, sizeof(s));
    memset(&cfg, 0, sizeof(cfg));
    cfg.n_peers           = 3;
    cfg.self_idx          = 0;
    cfg.initial_term      = 5;
    cfg.initial_voted_for = 1;
    cfg.cbs               = &cbs;

    int rc = raft_init(&s, &cfg);
    TEST_ASSERT_EQUAL_INT(0, rc);

    /* manually set a few fields to distinguish from zero defaults */
    s.votes_granted    = 2;
    s.election_decided = 1;
    s.voted_for_term   = 5;

    memset(&snap, 0xFF, sizeof(snap)); /* canary */
    raft_snapshot(&s, &snap);

    TEST_ASSERT_EQUAL_UINT64(5, snap.term);
    TEST_ASSERT_EQUAL_INT(RAFT_FOLLOWER, snap.role);
    TEST_ASSERT_EQUAL_INT(1, snap.voted_for);
    TEST_ASSERT_EQUAL_UINT64(5, snap.voted_for_term);
    TEST_ASSERT_EQUAL_INT(2, snap.votes_granted);
    TEST_ASSERT_EQUAL_INT(1, snap.election_decided);
}

/* ---------- test_raft entry point ---------- */

void test_raft(void)
{
    printf("\n>> raft test\n\n");

    RUN_TEST(test_raft_init_null_send_vote_request_returns_einval);
    RUN_TEST(test_raft_init_null_become_leader_returns_einval);
    RUN_TEST(test_raft_init_null_become_follower_returns_einval);
    RUN_TEST(test_raft_init_null_persist_returns_einval);
    RUN_TEST(test_raft_init_null_schedule_timeout_returns_einval);
    RUN_TEST(test_raft_init_null_cancel_timeout_returns_einval);
    RUN_TEST(test_raft_init_null_start_election_after_delay_returns_einval);
    RUN_TEST(test_raft_init_zero_peers_returns_einval);
    RUN_TEST(test_raft_init_success_fields);
    RUN_TEST(test_raft_init_default_election_timeout);
    RUN_TEST(test_raft_init_optional_callbacks_null_succeeds);
    RUN_TEST(test_raft_snapshot_returns_current_state);

    /* raft_start_election (task 3.2) */
    RUN_TEST(test_start_election_from_follower_3node);
    RUN_TEST(test_start_election_single_node);
    RUN_TEST(test_start_election_already_candidate);
    RUN_TEST(test_start_election_already_leader);

    /* raft_on_vote_request (task 3.3) */
    RUN_TEST(test_vote_req_stale_term);
    RUN_TEST(test_vote_req_higher_term_updates_state);
    RUN_TEST(test_vote_req_same_term_already_voted_different);
    RUN_TEST(test_vote_req_same_term_idempotent_same_candidate);
    RUN_TEST(test_vote_req_leader_denies);
    RUN_TEST(test_vote_req_on_vote_eligible_denies);
    RUN_TEST(test_vote_req_on_vote_eligible_grants);
    RUN_TEST(test_vote_req_on_vote_eligible_null);
    RUN_TEST(test_vote_req_persist_fails);
    RUN_TEST(test_vote_req_reply_term_always_set);
}