#include "zigbee_client.h"

#include <stdio.h>
#include <string.h>
#include <time.h>

#include "cJSON.h"
#include "esp_log.h"
#include "esp_timer.h"
#include "freertos/FreeRTOS.h"
#include "freertos/semphr.h"
#include "mqtt_client.h"

static const char *TAG = "zigbee";

typedef struct {
    const char *name;
    const char *friendly;
} room_def_t;

#define ROOM_DEF_ENTRY(display, friendly_name) { display, friendly_name },
static const room_def_t s_rooms[] = {
    APP_ROOM_TABLE(ROOM_DEF_ENTRY)
};

static room_reading_t s_readings[ROOM_COUNT];
static SemaphoreHandle_t s_lock;
static esp_mqtt_client_handle_t s_client;
static volatile bool s_connected;

/* ------------------------------------------------------------ parsing --- */

/*
 * Match an incoming topic to a room.
 *
 * z2m publishes to <base>/<friendly_name>, and also to sub-topics such as
 * <base>/<friendly_name>/availability. Only the exact device topic carries
 * the state payload, so this compares the whole string rather than a prefix.
 */
static int room_for_topic(const char *topic, int topic_len)
{
    char expected[160];

    for (int i = 0; i < ROOM_COUNT; i++) {
        int n = snprintf(expected, sizeof(expected), "%s/%s",
                         APP_MQTT_BASE_TOPIC, s_rooms[i].friendly);
        if (n == topic_len && strncmp(topic, expected, (size_t)topic_len) == 0) {
            return i;
        }
    }
    return -1;
}

/*
 * struct tm -> epoch seconds, interpreting the fields as UTC.
 *
 * timegm() is not in ESP-IDF's newlib, and mktime() is not a substitute: it
 * would apply APP_TIMEZONE to a timestamp that z2m already emitted in UTC,
 * shifting every reading's apparent age by the local offset. On a US Central
 * install that is six hours, which would make live sensors look stale and trip
 * the fallback ladder permanently.
 *
 * Days-from-civil (Howard Hinnant) avoids both problems and has no state.
 */
static int64_t tm_to_epoch_utc(const struct tm *t)
{
    int y = t->tm_year + 1900;
    unsigned m = (unsigned)t->tm_mon + 1;
    unsigned d = (unsigned)t->tm_mday;

    y -= (m <= 2);
    const int era = (y >= 0 ? y : y - 399) / 400;
    const unsigned yoe = (unsigned)(y - era * 400);
    const unsigned doy = (153u * (m + (m > 2 ? -3u : 9u)) + 2u) / 5u + d - 1u;
    const unsigned doe = yoe * 365u + yoe / 4u - yoe / 100u + doy;
    const int64_t days = (int64_t)era * 146097 + (int64_t)doe - 719468;

    return days * 86400 + t->tm_hour * 3600 + t->tm_min * 60 + t->tm_sec;
}

/*
 * z2m reports last_seen either as an ISO-8601 string or as epoch milliseconds,
 * depending on the `last_seen` advanced setting. Handle both, and treat
 * anything unparseable as absent rather than as zero age.
 */
static bool parse_sensor_age(const cJSON *root, uint32_t *age_s)
{
    const cJSON *ls = cJSON_GetObjectItemCaseSensitive(root, "last_seen");
    if (!ls) {
        return false;
    }

    time_t now = time(NULL);
    /* Before SNTP has synced, wall-clock time is meaningless and any age we
     * computed would be nonsense. Report absent. */
    if (now < 1600000000) {
        return false;
    }

    time_t seen = 0;

    if (cJSON_IsNumber(ls)) {
        seen = (time_t)(ls->valuedouble / 1000.0);
    } else if (cJSON_IsString(ls) && ls->valuestring) {
        struct tm tm = {0};
        const char *rest = strptime(ls->valuestring, "%Y-%m-%dT%H:%M:%S", &tm);
        if (!rest) {
            return false;
        }
        int64_t epoch = tm_to_epoch_utc(&tm);

        /*
         * Honour the offset suffix. z2m's ISO_8601 setting emits UTC ("Z"),
         * but ISO_8601_local emits local time with an offset ("-05:00").
         * Ignoring that suffix would shift every reading's apparent age by
         * the local offset — on a US install that is five or six hours, which
         * makes live sensors look stale and trips the fallback ladder
         * permanently. local = UTC + offset, so subtract it.
         */
        if (*rest == '.') {                     /* fractional seconds */
            rest++;
            while (*rest >= '0' && *rest <= '9') {
                rest++;
            }
        }
        if (*rest == '+' || *rest == '-') {
            int sign = (*rest == '-') ? -1 : 1;
            int oh = 0, om = 0;
            if (sscanf(rest + 1, "%2d:%2d", &oh, &om) < 1) {
                return false;
            }
            epoch -= (int64_t)sign * (oh * 3600 + om * 60);
        }
        /* 'Z' or nothing: already UTC. */

        seen = (time_t)epoch;
    } else {
        return false;
    }

    if (seen <= 0 || seen > now) {
        *age_s = 0;
        return true;
    }

    *age_s = (uint32_t)(now - seen);
    return true;
}

static void handle_payload(int room, const char *data, int len)
{
    cJSON *root = cJSON_ParseWithLength(data, (size_t)len);
    if (!root) {
        ESP_LOGW(TAG, "%s: unparseable payload", s_rooms[room].name);
        return;
    }

    const cJSON *temp = cJSON_GetObjectItemCaseSensitive(root, "temperature");
    if (!cJSON_IsNumber(temp)) {
        /*
         * Not an error. z2m publishes on any attribute change, so a humidity
         * or link-quality update legitimately arrives with no temperature.
         * Leaving the previous reading untouched is the point — a partial
         * message must not age or clear good data.
         */
        cJSON_Delete(root);
        return;
    }

    room_reading_t r = {
        .valid = true,
        .temperature_c = (float)temp->valuedouble,
        .received_us = esp_timer_get_time(),
    };

    const cJSON *batt = cJSON_GetObjectItemCaseSensitive(root, "battery");
    if (cJSON_IsNumber(batt)) {
        r.has_battery = true;
        r.battery_percent = (int)batt->valuedouble;
    }

    uint32_t age = 0;
    if (parse_sensor_age(root, &age)) {
        r.has_sensor_age = true;
        r.sensor_age_at_receipt_s = age;
    }

    xSemaphoreTake(s_lock, portMAX_DELAY);
    /* Carry battery forward if this message did not include it. */
    if (!r.has_battery && s_readings[room].has_battery) {
        r.has_battery = true;
        r.battery_percent = s_readings[room].battery_percent;
    }
    s_readings[room] = r;
    xSemaphoreGive(s_lock);

    if (r.has_battery) {
        ESP_LOGI(TAG, "%s: %.1fC, battery %d%%",
                 s_rooms[room].name, r.temperature_c, r.battery_percent);
    } else {
        ESP_LOGI(TAG, "%s: %.1fC", s_rooms[room].name, r.temperature_c);
    }

    cJSON_Delete(root);
}

/* -------------------------------------------------------------- events -- */

static void mqtt_event_handler(void *args, esp_event_base_t base,
                               int32_t event_id, void *event_data)
{
    (void)args;
    (void)base;
    esp_mqtt_event_handle_t event = event_data;

    switch ((esp_mqtt_event_id_t)event_id) {
    case MQTT_EVENT_CONNECTED: {
        s_connected = true;
        ESP_LOGI(TAG, "broker connected");

        char topic[160];
        for (int i = 0; i < ROOM_COUNT; i++) {
            snprintf(topic, sizeof(topic), "%s/%s",
                     APP_MQTT_BASE_TOPIC, s_rooms[i].friendly);
            /* QoS 0 is right here: readings are periodic and a missed one
             * simply ages, which the control loop already handles. */
            esp_mqtt_client_subscribe(s_client, topic, 0);
            ESP_LOGI(TAG, "subscribed %s -> %s", topic, s_rooms[i].name);
        }
        break;
    }

    case MQTT_EVENT_DISCONNECTED:
        s_connected = false;
        /* Readings are deliberately left alone. They age; they are not
         * cleared. PRD 4.1. */
        ESP_LOGW(TAG, "broker disconnected — readings will age");
        break;

    case MQTT_EVENT_DATA: {
        int room = room_for_topic(event->topic, event->topic_len);
        if (room < 0) {
            break;
        }
        /*
         * Long payloads arrive in fragments. z2m sensor JSON is small enough
         * that this should not happen, but a silently truncated parse would be
         * a nasty way to find out otherwise.
         */
        if (event->data_len != event->total_data_len) {
            ESP_LOGW(TAG, "%s: fragmented payload (%d of %d), ignoring",
                     s_rooms[room].name, event->data_len, event->total_data_len);
            break;
        }
        handle_payload(room, event->data, event->data_len);
        break;
    }

    case MQTT_EVENT_ERROR:
        ESP_LOGW(TAG, "mqtt error");
        break;

    default:
        break;
    }
}

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

esp_err_t zigbee_client_init(void)
{
    if (s_client) {
        return ESP_OK;
    }

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

    esp_mqtt_client_config_t cfg = {
        .broker.address.uri = APP_MQTT_URI,
        .credentials = {
            .username = (sizeof(APP_MQTT_USER) > 1) ? APP_MQTT_USER : NULL,
            .authentication.password =
                (sizeof(APP_MQTT_PASS) > 1) ? APP_MQTT_PASS : NULL,
        },
        .session.keepalive = 60,
        .network.reconnect_timeout_ms = 10000,
        .network.disable_auto_reconnect = false,
    };

    s_client = esp_mqtt_client_init(&cfg);
    if (!s_client) {
        ESP_LOGE(TAG, "client init failed");
        return ESP_FAIL;
    }

    ESP_ERROR_CHECK(esp_mqtt_client_register_event(
        s_client, ESP_EVENT_ANY_ID, mqtt_event_handler, NULL));

    /*
     * Start unconditionally, even with no WiFi yet. The client retries on its
     * own and must never block the control loop — PRD section 6.
     */
    esp_err_t err = esp_mqtt_client_start(s_client);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "client start failed: %s", esp_err_to_name(err));
        return err;
    }

    ESP_LOGI(TAG, "started, broker %s, %d room(s)", APP_MQTT_URI, ROOM_COUNT);
    return ESP_OK;
}

int zigbee_client_room_count(void)
{
    return ROOM_COUNT;
}

const char *zigbee_client_room_name(int idx)
{
    if (idx < 0 || idx >= ROOM_COUNT) {
        return "?";
    }
    return s_rooms[idx].name;
}

bool zigbee_client_get_reading(int idx, room_reading_t *out)
{
    if (idx < 0 || idx >= ROOM_COUNT || !out) {
        return false;
    }
    /* The UI and control loop both call this. If init failed we report "no
     * reading" and let the fallback ladder handle it, rather than taking a
     * NULL semaphore and crashing a device that controls heat. */
    if (!s_lock) {
        *out = (room_reading_t){0};
        return false;
    }

    xSemaphoreTake(s_lock, portMAX_DELAY);
    *out = s_readings[idx];
    xSemaphoreGive(s_lock);
    return true;
}

uint32_t zigbee_client_reading_age_s(int idx)
{
    room_reading_t r;
    if (!zigbee_client_get_reading(idx, &r) || !r.valid) {
        return UINT32_MAX;
    }

    uint32_t local = (uint32_t)((esp_timer_get_time() - r.received_us) / 1000000);
    return r.has_sensor_age ? local + r.sensor_age_at_receipt_s : local;
}

bool zigbee_client_is_connected(void)
{
    return s_connected;
}

int zigbee_client_lowest_battery(void)
{
    int lowest = -1;

    if (!s_lock) {
        return -1;
    }

    xSemaphoreTake(s_lock, portMAX_DELAY);
    for (int i = 0; i < ROOM_COUNT; i++) {
        if (s_readings[i].valid && s_readings[i].has_battery) {
            if (lowest < 0 || s_readings[i].battery_percent < lowest) {
                lowest = s_readings[i].battery_percent;
            }
        }
    }
    xSemaphoreGive(s_lock);

    return lowest;
}