/**
 * @packageDocumentation
 *
 * Configure your libp2p node with Prometheus metrics:
 *
 * ```typescript
 * import { createLibp2p } from 'libp2p'
 * import { prometheusMetrics } from '@libp2p/prometheus-metrics'
 *
 * const node = await createLibp2p({
 *   metrics: prometheusMetrics()
 * })
 * ```
 *
 * Then use the `prom-client` module to supply metrics to the Prometheus/Graphana client using your http framework:
 *
 * ```JavaScript
 * import client from 'prom-client'
 *
 * async function handler (request, h) {
 *   return h.response(await client.register.metrics())
 *     .type(client.register.contentType)
 * }
 * ```
 *
 * All Prometheus metrics are global so there's no other work required to extract them.
 *
 * ## Queries
 *
 * Some useful queries are:
 *
 * ### Data sent/received
 *
 * ```
 * rate(libp2p_data_transfer_bytes_total[30s])
 * ```
 *
 * ### CPU usage
 *
 * ```
 * rate(process_cpu_user_seconds_total[30s]) * 100
 * ```
 *
 * ### Memory usage
 *
 * ```
 * nodejs_memory_usage_bytes
 * ```
 *
 * ### DHT query time
 *
 * ```
 * libp2p_kad_dht_wan_query_time_seconds
 * ```
 *
 * or
 *
 * ```
 * libp2p_kad_dht_lan_query_time_seconds
 * ```
 *
 * ### TCP transport dialer errors
 *
 * ```
 * rate(libp2p_tcp_dialer_errors_total[30s])
 * ```
 */

import { statfs } from 'node:fs/promises'
import { totalmem } from 'node:os'
import { serviceCapabilities } from '@libp2p/interface'
import { collectDefaultMetrics, register } from 'prom-client'
import { PrometheusCounterGroup } from './counter-group.ts'
import { PrometheusCounter } from './counter.ts'
import { PrometheusHistogramGroup } from './histogram-group.ts'
import { PrometheusHistogram } from './histogram.ts'
import { PrometheusMetricGroup } from './metric-group.ts'
import { PrometheusMetric } from './metric.ts'
import { PrometheusSummaryGroup } from './summary-group.ts'
import { PrometheusSummary } from './summary.ts'
import type { ComponentLogger, Logger, MultiaddrConnection, Stream, CalculatedMetricOptions, Counter, CounterGroup, Metric, MetricGroup, MetricOptions, Metrics, CalculatedHistogramOptions, CalculatedSummaryOptions, HistogramOptions, Histogram, HistogramGroup, SummaryOptions, Summary, SummaryGroup, MessageStream } from '@libp2p/interface'
import type { DefaultMetricsCollectorConfiguration, Registry, RegistryContentType } from 'prom-client'

// export helper functions for creating buckets
export { linearBuckets, exponentialBuckets } from 'prom-client'

// prom-client metrics are global
const metrics = new Map<string, any>()

export interface PrometheusMetricsInit {
  /**
   * Use a custom registry to register metrics.
   * By default, the global registry is used to register metrics.
   */
  registry?: Registry

  /**
   * By default we collect default metrics - CPU, memory etc, to not do
   * this, pass true here
   */
  collectDefaultMetrics?: boolean

  /**
   * prom-client options to pass to the `collectDefaultMetrics` function
   */
  defaultMetrics?: DefaultMetricsCollectorConfiguration<RegistryContentType>

  /**
   * All metrics in prometheus are global so to prevent clashes in naming
   * we reset the global metrics registry on creation - to not do this,
   * pass true here
   */
  preserveExistingMetrics?: boolean

  /**
   * The current filesystem usage is reported as the metric
   * `nodejs_fs_usage_bytes` using the `statfs` function from `node:fs` - the
   * default location to stat is the current working directory, configured this
   * location here
   */
  statfsLocation?: string
}

export interface PrometheusCalculatedMetricOptions<T=number> extends CalculatedMetricOptions<T> {
  registry?: Registry
}

export interface PrometheusCalculatedHistogramOptions<T=number> extends CalculatedHistogramOptions<T> {
  registry?: Registry
}

export interface PrometheusCalculatedSummaryOptions<T=number> extends CalculatedSummaryOptions<T> {
  registry?: Registry
}

export interface PrometheusMetricsComponents {
  logger: ComponentLogger
}

class PrometheusMetrics implements Metrics {
  private readonly log: Logger
  private transferStats: Map<string, number>
  private readonly registry?: Registry

  constructor (components: PrometheusMetricsComponents, init?: Partial<PrometheusMetricsInit>) {
    this.log = components.logger.forComponent('libp2p:prometheus-metrics')
    this.registry = init?.registry

    if (init?.preserveExistingMetrics !== true) {
      this.log('Clearing existing metrics')
      metrics.clear()
      register?.clear()
    }

    if (init?.collectDefaultMetrics !== false) {
      this.log('Collecting default metrics')
      collectDefaultMetrics({ ...init?.defaultMetrics, register: this.registry ?? init?.defaultMetrics?.register })
    }

    // holds global and per-protocol sent/received stats
    this.transferStats = new Map()

    this.log('Collecting data transfer metrics')
    this.registerCounterGroup('libp2p_data_transfer_bytes_total', {
      label: 'protocol',
      calculate: () => {
        const output: Record<string, number> = {}

        for (const [key, value] of this.transferStats.entries()) {
          output[key] = value
        }

        // reset counts for next time
        this.transferStats.clear()

        return output
      }
    })

    this.log('Collecting memory metrics')
    this.registerMetricGroup('nodejs_memory_usage_bytes', {
      label: 'memory',
      calculate: () => {
        return {
          ...process.memoryUsage()
        }
      }
    })
    const totalMemoryMetric = this.registerMetric('nodejs_memory_total_bytes')
    totalMemoryMetric.update(totalmem())

    this.log('Collecting filesystem metrics')
    this.registerMetricGroup('nodejs_fs_usage_bytes', {
      label: 'filesystem',
      calculate: async () => {
        const stats = await statfs(init?.statfsLocation ?? process.cwd())
        const total = stats.bsize * stats.blocks
        const available = stats.bsize * stats.bavail

        return {
          total,
          free: stats.bsize * stats.bfree,
          available,
          used: (available / total) * 100
        }
      }
    })
  }

  readonly [Symbol.toStringTag] = '@libp2p/metrics-prometheus'

  readonly [serviceCapabilities]: string[] = [
    '@libp2p/metrics'
  ]

  start (): void {

  }

  stop (): void {
    this.transferStats.clear()
  }

  /**
   * Increment the transfer stat for the passed key, making sure
   * it exists first
   */
  _incrementValue (key: string, value: number): void {
    const existing = this.transferStats.get(key) ?? 0

    this.transferStats.set(key, existing + value)
  }

  /**
   * Override the sink/source of the stream to count the bytes
   * in and out
   */
  _track (stream: MessageStream, name: string): void {
    // Do not attach a `message` listener here.
    //
    // AbstractMessageStream dispatches buffered inbound data only when there is
    // at least one `message` listener. Adding a metrics listener too early can
    // cause the read buffer to be consumed before protocol handlers attach their
    // own readers (e.g. identify), leading to lost first frames.
    //
    // Instead, wrap dispatchEvent to observe already-dispatched message events
    // without increasing listenerCount('message').
    const dispatchEvent = stream.dispatchEvent.bind(stream)
    stream.dispatchEvent = (evt: Event): boolean => {
      if (evt.type === 'message') {
        this._incrementValue(`${name} received`, (evt as MessageEvent<{ byteLength: number }>).data.byteLength)
      }

      return dispatchEvent(evt)
    }

    const send = stream.send.bind(stream)
    stream.send = (buf) => {
      this._incrementValue(`${name} sent`, buf.byteLength)

      return send(buf)
    }
  }

  trackMultiaddrConnection (maConn: MultiaddrConnection): void {
    this._track(maConn, 'global')
  }

  trackProtocolStream (stream: Stream): void {
    if (stream.protocol == null) {
      // protocol not negotiated yet, should not happen as the upgrader
      // calls this handler after protocol negotiation
      return
    }

    this._track(stream, stream.protocol)
  }

  registerMetric (name: string, opts: PrometheusCalculatedMetricOptions): void
  registerMetric (name: string, opts?: MetricOptions): Metric
  registerMetric (name: string, opts: any = {}): any {
    if (name == null || name.trim() === '') {
      throw new Error('Metric name is required')
    }

    let metric = metrics.get(name)

    if (metric != null) {
      this.log('reuse existing metric', name)
      return metric
    }

    this.log('register metric', name)
    metric = new PrometheusMetric(name, { registry: this.registry, ...opts })

    metrics.set(name, metric)

    if (opts.calculate == null) {
      return metric
    }
  }

  registerMetricGroup (name: string, opts: PrometheusCalculatedMetricOptions<Record<string, number>>): void
  registerMetricGroup (name: string, opts?: MetricOptions): MetricGroup
  registerMetricGroup (name: string, opts: any = {}): any {
    if (name == null || name.trim() === '') {
      throw new Error('Metric group name is required')
    }

    let metricGroup = metrics.get(name)

    if (metricGroup != null) {
      this.log('reuse existing metric', name)
      return metricGroup
    }

    this.log('register metric group', name)
    metricGroup = new PrometheusMetricGroup(name, { registry: this.registry, ...opts })

    metrics.set(name, metricGroup)

    if (opts.calculate == null) {
      return metricGroup
    }
  }

  registerCounter (name: string, opts: PrometheusCalculatedMetricOptions): void
  registerCounter (name: string, opts?: MetricOptions): Counter
  registerCounter (name: string, opts: any = {}): any {
    if (name == null || name.trim() === '') {
      throw new Error('Counter name is required')
    }

    let counter = metrics.get(name)

    if (counter != null) {
      this.log('reuse existing counter', name)
      return counter
    }

    this.log('register counter', name)
    counter = new PrometheusCounter(name, { registry: this.registry, ...opts })

    metrics.set(name, counter)

    if (opts.calculate == null) {
      return counter
    }
  }

  registerCounterGroup (name: string, opts: PrometheusCalculatedMetricOptions<Record<string, number>>): void
  registerCounterGroup (name: string, opts?: MetricOptions): CounterGroup
  registerCounterGroup (name: string, opts: any = {}): any {
    if (name == null || name.trim() === '') {
      throw new Error('Counter group name is required')
    }

    let counterGroup = metrics.get(name)

    if (counterGroup != null) {
      this.log('reuse existing counter group', name)
      return counterGroup
    }

    this.log('register counter group', name)
    counterGroup = new PrometheusCounterGroup(name, { registry: this.registry, ...opts })

    metrics.set(name, counterGroup)

    if (opts.calculate == null) {
      return counterGroup
    }
  }

  registerHistogram (name: string, opts: PrometheusCalculatedHistogramOptions): void
  registerHistogram (name: string, opts?: HistogramOptions): Histogram
  registerHistogram (name: string, opts: any = {}): any {
    if (name == null || name.trim() === '') {
      throw new Error('Histogram name is required')
    }

    let metric = metrics.get(name)

    if (metric != null) {
      this.log('reuse existing histogram', name)
      return metric
    }

    this.log('register histogram', name)
    metric = new PrometheusHistogram(name, { registry: this.registry, ...opts })

    metrics.set(name, metric)

    if (opts.calculate == null) {
      return metric
    }
  }

  registerHistogramGroup (name: string, opts: PrometheusCalculatedHistogramOptions<Record<string, number>>): void
  registerHistogramGroup (name: string, opts?: HistogramOptions): HistogramGroup
  registerHistogramGroup (name: string, opts: any = {}): any {
    if (name == null || name.trim() === '') {
      throw new Error('Histogram group name is required')
    }

    let metricGroup = metrics.get(name)

    if (metricGroup != null) {
      this.log('reuse existing histogram group', name)
      return metricGroup
    }

    this.log('register histogram group', name)
    metricGroup = new PrometheusHistogramGroup(name, { registry: this.registry, ...opts })

    metrics.set(name, metricGroup)

    if (opts.calculate == null) {
      return metricGroup
    }
  }

  registerSummary (name: string, opts: PrometheusCalculatedSummaryOptions): void
  registerSummary (name: string, opts?: SummaryOptions): Summary
  registerSummary (name: string, opts: any = {}): any {
    if (name == null || name.trim() === '') {
      throw new Error('Summary name is required')
    }

    let metric = metrics.get(name)

    if (metric != null) {
      this.log('reuse existing summary', name)
      return metric
    }

    this.log('register summary', name)
    metric = new PrometheusSummary(name, { registry: this.registry, ...opts })

    metrics.set(name, metric)

    if (opts.calculate == null) {
      return metric
    }
  }

  registerSummaryGroup (name: string, opts: PrometheusCalculatedSummaryOptions<Record<string, number>>): void
  registerSummaryGroup (name: string, opts?: SummaryOptions): SummaryGroup
  registerSummaryGroup (name: string, opts: any = {}): any {
    if (name == null || name.trim() === '') {
      throw new Error('Summary group name is required')
    }

    let metricGroup = metrics.get(name)

    if (metricGroup != null) {
      this.log('reuse existing summary group', name)
      return metricGroup
    }

    this.log('register summary group', name)
    metricGroup = new PrometheusSummaryGroup(name, { registry: this.registry, ...opts })

    metrics.set(name, metricGroup)

    if (opts.calculate == null) {
      return metricGroup
    }
  }

  createTrace (): any {
    // no-op
  }

  traceFunction <T extends (...args: any[]) => any> (name: string, fn: T): T {
    // no-op
    return fn
  }
}

export function prometheusMetrics (init?: Partial<PrometheusMetricsInit>): (components: PrometheusMetricsComponents) => Metrics {
  return (components) => {
    return new PrometheusMetrics(components, init)
  }
}