import { PrometheusMetricsConfig } from '@n8n/config';
import { Time } from '@n8n/constants';
import { WorkflowRepository } from '@n8n/db';
import { Service } from '@n8n/di';
import { InstanceSettings } from 'n8n-core';
import promClient from 'prom-client';

import { CacheService } from '@/services/cache/cache.service';

import type { PrometheusMetricsCollector } from './base';
import { CachedMetricQuery } from './cached-metric-query';

type WorkflowInfoGaugeParams = {
	name: string;
	help: string;
	cacheKey: string;
	activeOnly: boolean;
};

/**
 * Exposes gauges that map workflow IDs to their human-readable names, enabling
 * dashboards to resolve IDs to names without extra lookups.
 *
 * Only the leader reports, as the mapping is instance-wide state.
 *
 * Results are cached to avoid hitting the database on every metrics scrape;
 * cache TTL is controlled by `endpoints.metrics.workflowInfoMetricInterval`.
 */
@Service()
export class PrometheusWorkflowInfoMetricsService implements PrometheusMetricsCollector {
	constructor(
		private readonly config: PrometheusMetricsConfig,
		private readonly workflowRepository: WorkflowRepository,
		private readonly cacheService: CacheService,
		private readonly instanceSettings: InstanceSettings,
	) {}

	get enabled(): boolean {
		return this.config.includeWorkflowInfoMetrics;
	}

	init() {
		this.initGauge({
			name: 'workflow_info',
			help: 'Map of workflow ID to name. Reported by the leader main only.',
			cacheKey: 'metrics:workflow-info:v2',
			activeOnly: false,
		});
		this.initGauge({
			name: 'active_workflow_info',
			help: 'Map of active workflow ID to name. Reported by the leader main only.',
			cacheKey: 'metrics:active-workflow-info:v1',
			activeOnly: true,
		});
	}

	private initGauge({ name, help, cacheKey, activeOnly }: WorkflowInfoGaugeParams) {
		const { instanceSettings } = this;
		const cacheTtl = this.config.workflowInfoMetricInterval * Time.seconds.toMilliseconds;
		const query = new CachedMetricQuery<Array<{ id: string; name: string }>>({
			cacheService: this.cacheService,
			cacheKey,
			ttlMs: cacheTtl,
			query: async () => await this.workflowRepository.getWorkflowInfo({ activeOnly }),
		});

		new promClient.Gauge({
			name: `${this.config.prefix}${name}`,
			help,
			labelNames: ['workflow_id', 'workflow_name'],
			async collect() {
				this.reset();

				if (!instanceSettings.isLeader) return;

				const workflows = await query.get();
				for (const { id, name: workflowName } of workflows) {
					this.labels({ workflow_id: id, workflow_name: workflowName }).set(1);
				}
			},
		});
	}
}