const axios = require('axios');
const cache = require('./cache');
const db = require('./db');

const POLL_INTERVAL = 10000; // 10 seconds

async function pollLatency() {
    try {
        const [routes] = await db.query(`
            SELECT r.*, s.url 
            FROM latency_routes r 
            JOIN prometheus_sources s ON r.source_id = s.id
            WHERE s.type = 'blackbox'
        `);

        if (routes.length === 0) return;

        // Poll each route
        await Promise.allSettled(routes.map(async (route) => {
            try {
                // Blackbox exporter probe URL
                // We assume ICMP module for now. If target is a URL, maybe use http_2xx
                let module = 'icmp';
                let target = route.latency_target;
                
                if (target.startsWith('http://') || target.startsWith('https://')) {
                    module = 'http_2xx';
                }

                const probeUrl = `${route.url.replace(/\/+$/, '')}/probe?module=${module}&target=${encodeURIComponent(target)}`;
                
                const startTime = Date.now();
                const response = await axios.get(probeUrl, { timeout: 5000 });

                // 1. Parse prometheus text format for success and specific metrics
                let latency = null;
                const lines = response.data.split('\n').map(l => l.trim()).filter(l => l && !l.startsWith('#'));
                
                // Track success but also try to parse latency anyway as a backup
                let isProbeSuccess = false;
                for (const line of lines) {
                    if (line.match(/^probe_success(\{.*\})?\s+1/)) {
                        isProbeSuccess = true;
                        break;
                    }
                }

                // Try a wider set of potential latency metrics
                const targetMetrics = [
                    'probe_icmp_duration_seconds', 
                    'probe_http_duration_seconds', 
                    'probe_dns_lookup_time_seconds',
                    'probe_duration_seconds'
                ];

                for (const metricName of targetMetrics) {
                    // Match: metric_name{labels} value
                    // Regex handles optional labels and scientific notation
                    const regex = new RegExp(`^${metricName}(?:\\{[^}]*\\})?\\s+([\\d.eE+-]+)`);
                    for (const line of lines) {
                        const match = line.match(regex);
                        if (match) {
                            const val = parseFloat(match[1]);
                            if (!isNaN(val)) {
                                latency = val * 1000; // to ms
                                break;
                            }
                        }
                    }
                    if (latency !== null) break;
                }

                // If probe reported failure but we found a duration, we might still want to show null/error
                if (!isProbeSuccess && latency !== null) {
                    // If probe failed, force null to indicate error/offline on UI
                    latency = null;
                }

                // Save to Valkey
                await cache.set(`latency:route:${route.id}`, latency, 60);
                // console.log(`[Latency] Route ${route.id} (${target}): ${latency.toFixed(2)}ms`);
            } catch (err) {
                // console.error(`[Latency] Error polling route ${route.id}:`, err.message);
                await cache.set(`latency:route:${route.id}`, null, 60);
            }
        }));
    } catch (err) {
        console.error('[Latency] Service error:', err.message);
    }
}

let intervalId = null;

function start() {
    if (intervalId) clearInterval(intervalId);
    pollLatency(); // initial run
    intervalId = setInterval(pollLatency, POLL_INTERVAL);
    console.log('[Latency] Background service started (polling Blackbox Exporter directly)');
}

module.exports = {
    start
};