const fs = require('node:fs/promises');
const path = require('node:path');

const ROOT_DIRECTORY = path.join(__dirname, '..');
const NOTIFICATION_CONFIG_FILE = process.env.NOTIFICATION_CONFIG_FILE
    ? path.resolve(process.env.NOTIFICATION_CONFIG_FILE)
    : path.join(ROOT_DIRECTORY, 'config', 'notifications.json');

const SEVERITY_RANK = {
    RECOVERY: 0,
    NORMAL: 0,
    WARNING: 1,
    OFFLINE: 2,
    CRITICAL: 3
};

const DEFAULT_NOTIFICATION_CONFIG = {
    enabled: false,
    minSeverity: 'CRITICAL',
    channels: {
        webhook: {
            enabled: false,
            url: '',
            headers: {}
        },
        telegram: {
            enabled: false,
            botToken: '',
            chatId: ''
        }
    }
};

function mergeNotificationConfig(config = {}) {
    return {
        enabled: config.enabled === true,
        minSeverity: SEVERITY_RANK[config.minSeverity] === undefined
            ? DEFAULT_NOTIFICATION_CONFIG.minSeverity
            : config.minSeverity,
        channels: {
            webhook: {
                ...DEFAULT_NOTIFICATION_CONFIG.channels.webhook,
                ...(config.channels && config.channels.webhook)
            },
            telegram: {
                ...DEFAULT_NOTIFICATION_CONFIG.channels.telegram,
                ...(config.channels && config.channels.telegram)
            }
        }
    };
}

async function readNotificationConfig() {
    try {
        const rawConfig = await fs.readFile(NOTIFICATION_CONFIG_FILE, 'utf8');
        return mergeNotificationConfig(JSON.parse(rawConfig));
    } catch {
        return mergeNotificationConfig();
    }
}

function validateNotificationConfig(rawConfig) {
    const config = mergeNotificationConfig(rawConfig);

    if (SEVERITY_RANK[config.minSeverity] === undefined) {
        throw Object.assign(new Error('Severidad minima no valida.'), { status: 400 });
    }

    if (config.channels.webhook.enabled && !isValidHttpUrl(config.channels.webhook.url)) {
        throw Object.assign(new Error('URL de webhook no valida.'), { status: 400 });
    }

    if (config.channels.telegram.enabled) {
        if (!config.channels.telegram.botToken || !config.channels.telegram.chatId) {
            throw Object.assign(
                new Error('Telegram requiere botToken y chatId.'),
                { status: 400 }
            );
        }
    }

    if (
        config.channels.webhook.headers &&
        (typeof config.channels.webhook.headers !== 'object' ||
            Array.isArray(config.channels.webhook.headers))
    ) {
        throw Object.assign(new Error('Headers de webhook invalidos.'), { status: 400 });
    }

    return config;
}

async function writeNotificationConfig(rawConfig) {
    const config = validateNotificationConfig(rawConfig);

    await fs.mkdir(path.dirname(NOTIFICATION_CONFIG_FILE), { recursive: true });
    await fs.writeFile(
        NOTIFICATION_CONFIG_FILE,
        `${JSON.stringify(config, null, 4)}\n`,
        'utf8'
    );
    return config;
}

function redactNotificationConfig(config) {
    return {
        ...config,
        channels: {
            webhook: {
                ...config.channels.webhook,
                headers: Object.keys(config.channels.webhook.headers || {}).length > 0
                    ? '[configured]'
                    : {}
            },
            telegram: {
                ...config.channels.telegram,
                botToken: config.channels.telegram.botToken ? '[configured]' : ''
            }
        }
    };
}

function isValidHttpUrl(value) {
    try {
        const url = new URL(value);
        return ['http:', 'https:'].includes(url.protocol);
    } catch {
        return false;
    }
}

function shouldNotify(event, minSeverity) {
    const eventRank = SEVERITY_RANK[event.state] ?? 0;
    const minimumRank = SEVERITY_RANK[minSeverity] ?? SEVERITY_RANK.CRITICAL;

    return eventRank >= minimumRank;
}

function buildNotificationMessage(event) {
    const value = event.value === '' || event.value === null || event.value === undefined
        ? 'N/A'
        : event.value;

    return [
        `Photobioreactor alarm: ${event.state}`,
        `Sensor: ${event.sensorId || event.sensor}`,
        `Value: ${value}`,
        `Message: ${event.message}`,
        `Time: ${event.timestamp}`
    ].join('\n');
}

async function dispatchAlarmNotifications(events) {
    const config = await readNotificationConfig();

    if (!config.enabled || !Array.isArray(events) || events.length === 0) {
        return [];
    }

    const eligibleEvents = events.filter((event) =>
        shouldNotify(event, config.minSeverity)
    );
    const results = [];

    for (const event of eligibleEvents) {
        if (config.channels.webhook.enabled) {
            results.push(await sendSafely('webhook', event, () =>
                sendWebhookNotification(event, config.channels.webhook)
            ));
        }

        if (config.channels.telegram.enabled) {
            results.push(await sendSafely('telegram', event, () =>
                sendTelegramNotification(event, config.channels.telegram)
            ));
        }
    }

    return results;
}

async function sendSafely(channel, event, send) {
    try {
        await send();
        return {
            channel,
            sensorId: event.sensorId || event.sensor,
            state: event.state,
            success: true
        };
    } catch (error) {
        return {
            channel,
            sensorId: event.sensorId || event.sensor,
            state: event.state,
            success: false,
            error: error.message
        };
    }
}

async function sendWebhookNotification(event, channelConfig) {
    await postJson(channelConfig.url, {
        event,
        text: buildNotificationMessage(event)
    }, channelConfig.headers || {});
}

async function sendTelegramNotification(event, channelConfig) {
    const url = `https://api.telegram.org/bot${channelConfig.botToken}/sendMessage`;
    await postJson(url, {
        chat_id: channelConfig.chatId,
        text: buildNotificationMessage(event)
    });
}

async function postJson(url, payload, headers = {}) {
    if (typeof fetch !== 'function') {
        throw new Error('fetch no esta disponible en este runtime.');
    }

    const response = await fetch(url, {
        method: 'POST',
        headers: {
            'Content-Type': 'application/json',
            ...headers
        },
        body: JSON.stringify(payload)
    });

    if (!response.ok) {
        throw new Error(`HTTP ${response.status}`);
    }
}

module.exports = {
    DEFAULT_NOTIFICATION_CONFIG,
    NOTIFICATION_CONFIG_FILE,
    dispatchAlarmNotifications,
    readNotificationConfig,
    redactNotificationConfig,
    shouldNotify,
    validateNotificationConfig,
    writeNotificationConfig
};