#include "relay.h"

#include <inttypes.h>

#include "esp_check.h"
#include "esp_log.h"
#include "esp_task_wdt.h"
#include "esp_timer.h"
#include "freertos/FreeRTOS.h"
#include "freertos/semphr.h"
#include "freertos/task.h"
#include "pcf8574.h"

static const char *TAG = "relay";

/* The module is active low: pin low closes the contact. */
#define RELAY_PIN_ASSERTED      false
#define RELAY_PIN_DEASSERTED    true

/*
 * 250ms. Fast enough that max-on-time and the watchdog are enforced with
 * sub-second precision, slow enough to be free.
 */
#define SAFETY_TICK_MS          250

/* Ring of call-start timestamps, for the trailing-hour cycle count. */
#define CYCLE_HISTORY_LEN       8

static SemaphoreHandle_t s_lock;
static bool s_initialised;

static bool s_heat_on;
static bool s_requested;
static bool s_ever_requested;   /* control loop has called in at least once */
static relay_fault_t s_fault;

static int64_t s_boot_us;
static int64_t s_last_request_us;
static int64_t s_on_since_us;       /* valid while s_heat_on */
static int64_t s_off_since_us;      /* when the last call ended, or boot */
static int64_t s_last_start_us;     /* start of the most recent call, 0=never */

static int64_t s_cycle_starts[CYCLE_HISTORY_LEN];
static uint8_t s_cycle_next;

static inline int64_t now_us(void)
{
    return esp_timer_get_time();
}

static inline uint32_t secs_since(int64_t then_us)
{
    if (then_us == 0) {
        return UINT32_MAX;
    }
    int64_t d = now_us() - then_us;
    return (d < 0) ? 0 : (uint32_t)(d / 1000000);
}

/* ------------------------------------------------------------- output --- */

/*
 * The one place that touches the pin.
 *
 * A failure to close the contact is a comfort problem. A failure to open it is
 * the problem this whole module exists to prevent, so opening retries hard and
 * escalates the log level.
 */
static esp_err_t drive_pin(bool asserted)
{
    const int attempts = asserted ? 1 : 5;
    esp_err_t err = ESP_FAIL;

    for (int i = 0; i < attempts; i++) {
        err = pcf8574_write(PCF_PIN_RELAY,
                            asserted ? RELAY_PIN_ASSERTED : RELAY_PIN_DEASSERTED);
        if (err == ESP_OK) {
            return ESP_OK;
        }
        if (!asserted) {
            ESP_LOGE(TAG, "FAILED TO OPEN CONTACT (attempt %d/%d): %s",
                     i + 1, attempts, esp_err_to_name(err));
            vTaskDelay(pdMS_TO_TICKS(20));
        }
    }

    return err;
}

esp_err_t relay_emergency_off(void)
{
    esp_err_t err = drive_pin(false);

    if (s_lock) {
        xSemaphoreTake(s_lock, portMAX_DELAY);
    }
    s_heat_on = false;
    s_requested = false;
    if (err != ESP_OK) {
        s_fault = RELAY_FAULT_IO;
    }
    if (s_lock) {
        xSemaphoreGive(s_lock);
    }

    return err;
}

/* -------------------------------------------------------------- gating -- */

/* Seconds still to wait before a new call may start. Caller holds the lock. */
static uint32_t hold_off_remaining_locked(void)
{
    uint32_t worst = 0;

    uint32_t since_boot = secs_since(s_boot_us);
    if (since_boot < RELAY_STARTUP_LOCKOUT_S) {
        worst = RELAY_STARTUP_LOCKOUT_S - since_boot;
    }

    uint32_t off_for = secs_since(s_off_since_us);
    if (off_for < RELAY_MIN_OFF_TIME_S) {
        uint32_t r = RELAY_MIN_OFF_TIME_S - off_for;
        if (r > worst) {
            worst = r;
        }
    }

    if (s_last_start_us != 0) {
        uint32_t since_start = secs_since(s_last_start_us);
        if (since_start < RELAY_MIN_CYCLE_PERIOD_S) {
            uint32_t r = RELAY_MIN_CYCLE_PERIOD_S - since_start;
            if (r > worst) {
                worst = r;
            }
        }
    }

    return worst;
}

static uint8_t cycles_last_hour_locked(void)
{
    int64_t cutoff = now_us() - (int64_t)3600 * 1000000;
    uint8_t n = 0;

    for (int i = 0; i < CYCLE_HISTORY_LEN; i++) {
        if (s_cycle_starts[i] != 0 && s_cycle_starts[i] >= cutoff) {
            n++;
        }
    }
    return n;
}

/* --------------------------------------------------------- transitions -- */

static void turn_on_locked(void)
{
    if (drive_pin(true) != ESP_OK) {
        s_fault = RELAY_FAULT_IO;
        ESP_LOGE(TAG, "could not close contact");
        return;
    }

    s_heat_on = true;
    s_on_since_us = now_us();
    s_last_start_us = s_on_since_us;

    s_cycle_starts[s_cycle_next] = s_on_since_us;
    s_cycle_next = (uint8_t)((s_cycle_next + 1) % CYCLE_HISTORY_LEN);

    /* A successful start means whatever held us off has cleared. */
    if (s_fault != RELAY_FAULT_IO) {
        s_fault = RELAY_FAULT_NONE;
    }

    ESP_LOGI(TAG, "HEAT ON  (cycles in last hour: %u)",
             (unsigned)cycles_last_hour_locked());
}

static void turn_off_locked(relay_fault_t reason)
{
    if (drive_pin(false) != ESP_OK) {
        s_fault = RELAY_FAULT_IO;
        return;
    }

    uint32_t ran = secs_since(s_on_since_us);
    s_heat_on = false;
    s_off_since_us = now_us();

    if (reason != RELAY_FAULT_NONE) {
        s_fault = reason;
        ESP_LOGW(TAG, "HEAT OFF after %" PRIu32 "s — %s",
                 ran, relay_fault_str(reason));
    } else {
        ESP_LOGI(TAG, "HEAT OFF after %" PRIu32 "s", ran);
    }
}

/* ---------------------------------------------------------- safety task -- */

static void safety_task(void *arg)
{
    (void)arg;

    esp_task_wdt_add(NULL);

    while (1) {
        esp_task_wdt_reset();

        xSemaphoreTake(s_lock, portMAX_DELAY);

        /*
         * Interlock 2 — watchdog. Checked before anything else, and it applies
         * whether or not heat is currently wanted: if the control loop has
         * gone silent we do not trust s_requested at all.
         */
        bool control_alive =
            secs_since(s_last_request_us) <= RELAY_WATCHDOG_TIMEOUT_S;

        if (!control_alive) {
            if (s_heat_on) {
                turn_off_locked(RELAY_FAULT_WATCHDOG);
            } else if (s_fault == RELAY_FAULT_NONE && s_ever_requested) {
                /*
                 * Only fault once the control loop has *stopped* talking.
                 * Before its first-ever call this is just boot ordering — the
                 * relay is held off regardless (the seeded-stale watchdog is
                 * the bounded-startup interlock), and flashing "control loop
                 * stopped" on every power-up would teach the user to ignore
                 * the one fault that matters most.
                 */
                s_fault = RELAY_FAULT_WATCHDOG;
            }
            s_requested = false;

        } else if (s_heat_on) {
            /* Interlock 3 — maximum on-time. */
            if (secs_since(s_on_since_us) >= RELAY_MAX_ON_TIME_S) {
                turn_off_locked(RELAY_FAULT_MAX_ON_TIME);
            } else if (!s_requested) {
                turn_off_locked(RELAY_FAULT_NONE);
            }

        } else {
            /* Off, and the control loop is alive. May we start? */
            if (s_requested && hold_off_remaining_locked() == 0) {
                turn_on_locked();
            }
        }

        xSemaphoreGive(s_lock);
        vTaskDelay(pdMS_TO_TICKS(SAFETY_TICK_MS));
    }
}

/* ----------------------------------------------------------------- api -- */

esp_err_t relay_init(void)
{
    if (s_initialised) {
        return ESP_OK;
    }

    if (!pcf8574_is_ready()) {
        ESP_LOGE(TAG, "expander not ready — refusing to arm");
        return ESP_ERR_INVALID_STATE;
    }

    s_lock = xSemaphoreCreateMutex();
    if (!s_lock) {
        return ESP_ERR_NO_MEM;
    }

    s_boot_us = now_us();
    s_off_since_us = s_boot_us;
    s_last_start_us = 0;
    s_heat_on = false;
    s_requested = false;
    s_ever_requested = false;
    s_fault = RELAY_FAULT_NONE;

    /*
     * Seed the watchdog as already stale. The relay therefore cannot close
     * until the control loop has actually called in once — PRD 5.6's bounded
     * startup state, enforced rather than assumed.
     */
    s_last_request_us = 0;

    ESP_RETURN_ON_ERROR(drive_pin(false), TAG, "initial de-assert");

    /* Priority above the UI: this task decides whether the house catches an
     * hour of unwanted heat, the UI decides whether a label repaints. */
    if (xTaskCreate(safety_task, "relay_safety", 3072, NULL, 6, NULL) != pdPASS) {
        ESP_LOGE(TAG, "safety task create failed");
        return ESP_ERR_NO_MEM;
    }

    s_initialised = true;
    ESP_LOGI(TAG, "armed — max on %us, min off %us, min cycle period %us, "
                  "startup lockout %us",
             RELAY_MAX_ON_TIME_S, RELAY_MIN_OFF_TIME_S,
             RELAY_MIN_CYCLE_PERIOD_S, RELAY_STARTUP_LOCKOUT_S);
    return ESP_OK;
}

void relay_request_heat(bool want_heat)
{
    if (!s_lock) {
        return;
    }

    xSemaphoreTake(s_lock, portMAX_DELAY);
    s_requested = want_heat;
    s_ever_requested = true;
    s_last_request_us = now_us();

    /* Recovering from a watchdog trip: the control loop is talking again. */
    if (s_fault == RELAY_FAULT_WATCHDOG) {
        s_fault = RELAY_FAULT_NONE;
    }
    xSemaphoreGive(s_lock);
}

bool relay_is_on(void)
{
    return s_heat_on;
}

void relay_status(relay_status_t *out)
{
    if (!out) {
        return;
    }
    if (!s_lock) {
        *out = (relay_status_t){0};
        return;
    }

    xSemaphoreTake(s_lock, portMAX_DELAY);
    out->heat_on = s_heat_on;
    out->heat_requested = s_requested;
    out->fault = s_fault;
    out->on_seconds = s_heat_on ? secs_since(s_on_since_us) : 0;
    out->off_seconds = s_heat_on ? 0 : secs_since(s_off_since_us);
    out->hold_off_seconds = s_heat_on ? 0 : hold_off_remaining_locked();
    out->cycles_last_hour = cycles_last_hour_locked();
    xSemaphoreGive(s_lock);
}

const char *relay_fault_str(relay_fault_t fault)
{
    switch (fault) {
    case RELAY_FAULT_NONE:          return "none";
    case RELAY_FAULT_WATCHDOG:      return "control loop stopped";
    case RELAY_FAULT_MAX_ON_TIME:   return "max on-time exceeded";
    case RELAY_FAULT_IO:            return "expander I/O error";
    default:                        return "unknown";
    }
}