#include "guard.h"
#include <string.h>
#include <limits.h>

void history_add(history_t *h, double at, uint64_t value)
{
    h->p[h->next].at = at; h->p[h->next].value = value;
    h->next = (h->next + 1) % HIST;
    if (h->count < HIST) h->count++;
}

delta_t history_delta(const history_t *h, double now, unsigned seconds)
{
    delta_t d = {0, 0, 0};
    unsigned i, latest;
    double best = 1.25;
    if (h->count < 2) return d;
    latest = (h->next + HIST - 1) % HIST;
    if (now - h->p[latest].at > 1.25) return d;
    for (i = 0; i < h->count; i++) {
        double age = h->p[latest].at - h->p[i].at;
        double error = age - seconds;
        if (error < 0) error = -error;
        if (age > 0 && error < best && h->p[i].value <= INT64_MAX &&
            h->p[latest].value <= INT64_MAX) {
            best = error; d.valid = 1; d.age = age;
            d.value = (int64_t)h->p[latest].value - (int64_t)h->p[i].value;
        }
    }
    return d;
}

uint64_t rank_score(uint64_t rss, delta_t growth)
{
    uint64_t add = growth.valid && growth.value > 0 ? (uint64_t)growth.value : 0;
    if (add > (UINT64_MAX - rss) / 2) return UINT64_MAX;
    return rss + 2 * add;
}

int swap_physical_bytes_from_blocks(uint64_t total_blocks,
    uint64_t free_blocks, uint64_t *bytes)
{
    uint64_t used;
    if (!bytes || free_blocks > total_blocks) return -1;
    used = total_blocks - free_blocks;
    if (used > UINT64_MAX / 512) return -1;
    *bytes = used * 512;
    return 0;
}

const char *state_name(enum state s)
{
    static const char *names[] = {"NORMAL", "PRE-PRESSURE", "PRESSURE",
        "CRITICAL", "EMERGENCY", "RECOVERY"};
    return names[s];
}

void engine_init(engine_t *e)
{
    memset(e, 0, sizeof (*e));
    engine_gap(e);
}

void engine_gap(engine_t *e)
{
    e->low_since = e->critical_since = e->recovery_since = -1;
    e->have_last = 0; e->danger = 0; e->floor = 0;
}

void engine_step(engine_t *e, const config_t *c, const sample_t *s,
    delta_t free_d5, delta_t physical_swap_d5, delta_t pageout_d5)
{
    int stress;
    enum state desired = NORMAL;
    if (e->have_last && (s->at - e->last_at > 2.5 || s->at <= e->last_at))
        engine_gap(e);
    /* Physical swap growth is corroboration only, never an independent trigger. */
    stress = s->scan > 0 || (free_d5.valid && free_d5.value < 0) ||
        (e->have_last && s->free < e->last_free) ||
        (physical_swap_d5.valid && physical_swap_d5.value > 0 &&
        pageout_d5.valid && pageout_d5.value > 0 && s->free < s->lots);
    e->floor = s->free < s->min / 2;
    if (s->free < s->lots) {
        if (e->low_since < 0) e->low_since = s->at;
    } else e->low_since = -1;
    if (s->free < s->des && stress) {
        if (e->critical_since < 0) e->critical_since = s->at;
    } else e->critical_since = -1;
    if (e->low_since >= 0 && s->at - e->low_since >= c->pre_s)
        desired = PRE_PRESSURE;
    if (e->low_since >= 0 && s->at - e->low_since >= c->pressure_s && stress)
        desired = PRESSURE;
    if (e->critical_since >= 0 && s->at - e->critical_since >= c->critical_s)
        desired = CRITICAL;
    if (s->free < s->min) desired = EMERGENCY;
    e->danger = desired == CRITICAL || desired == EMERGENCY;
    /* State hysteresis never authorizes an action on its own. */
    if (desired >= PRE_PRESSURE && desired <= EMERGENCY) {
        e->recovery_since = -1;
        if (e->state == RECOVERY || desired > e->state) e->state = desired;
    }
    if (s->free >= s->lots && e->state != NORMAL) {
        e->state = RECOVERY;
        /* 10% exit margin, and no active scanner, for a full recovery. */
        if (s->free - s->lots >= s->lots / 10 && s->scan == 0) {
            if (e->recovery_since < 0) e->recovery_since = s->at;
            if (s->at - e->recovery_since >= c->recovery_s) e->state = NORMAL;
        } else e->recovery_since = -1;
    } else if (s->free < s->lots) {
        e->recovery_since = -1;
        if (e->state == RECOVERY) e->state = PRE_PRESSURE;
    }
    e->last_at = s->at; e->last_free = s->free; e->have_last = 1;
}

int same_process(const process_t *a, const process_t *b)
{
    return a->pid == b->pid && a->start_sec == b->start_sec &&
        a->start_nsec == b->start_nsec && a->zid == b->zid &&
        a->zone_generation == b->zone_generation && !strcmp(a->uuid, b->uuid);
}

int was_victim(const controller_t *c, const process_t *p)
{
    unsigned i;
    for (i = 0; i < c->nvictims; i++)
        if (same_process(&c->victims[i], p)) return 1;
    return 0;
}

plan_t action_plan(controller_t *a, const config_t *c, const engine_t *e,
    const sample_t *s, const process_t *candidate)
{
    plan_t p;
    unsigned i, n = 0;
    memset(&p, 0, sizeof (p)); p.reason = "no_pressure";
    for (i = 0; i < a->nrate; i++)
        if (s->at - a->rate[i] < 60) a->rate[n++] = a->rate[i];
    a->nrate = n;
    if (e->state == NORMAL) a->nvictims = 0;
    if (s->free >= s->lots) a->has_pending = 0;
    if (!e->danger) return p;
    if (a->has_pending) {
        p.reason = "term_grace";
        if (e->floor || (s->free < s->min && s->at - a->term_at >= 1) ||
            s->at - a->term_at >= c->term_s) {
            p.target = a->pending; p.action = KILL;
            p.reason = e->floor ? "floor" : "memory_not_recovered";
        }
        return p;
    }
    if (a->nvictims >= c->max_victims || a->nrate >= c->max_per_minute) {
        p.reason = "victim_budget_exhausted"; return p;
    }
    /* Emergency bypasses the normal cooldown, not protection or budgets. */
    if (s->free >= s->min && s->at < a->next_at) {
        p.reason = "cooldown"; return p;
    }
    if (!candidate || protected_process(c, candidate) || was_victim(a, candidate)) {
        p.reason = "no_authorized_candidate"; return p;
    }
    p.target = *candidate;
    p.action = e->floor ? KILL : TERM;
    p.reason = e->floor ? "floor" : s->free < s->min ? "minfree" : "critical";
    return p;
}

void action_commit(controller_t *a, const config_t *c, const sample_t *s,
    const plan_t *p)
{
    if (p->action == NONE) return;
    if (!was_victim(a, &p->target)) {
        if (a->nvictims < MAX_VICTIMS) a->victims[a->nvictims++] = p->target;
        if (a->nrate < 64) a->rate[a->nrate++] = s->at;
    }
    a->next_at = s->at + c->cooldown_s;
    if (p->action == TERM) {
        a->pending = p->target; a->term_at = s->at; a->has_pending = 1;
    } else a->has_pending = 0;
}