require('bare-process/global')
const EventEmitter = require('bare-events')
const { assertNonEmpty } = require('../../_shared/lib/errors.js')

const PROTOCOL = 'sla-budget/v1'

class HyperP2PSlaBudget extends EventEmitter {
  constructor (opts = {}) {
    super()
    this._services = new Map()
    this._stats = { allocated: 0, consumed: 0, rejected: 0 }
  }

  allocate (service, tokens) {
    assertNonEmpty(service, 'service')
    const amount = Number(tokens)
    if (!Number.isFinite(amount) || amount < 0) {
      throw new Error('tokens must be a non-negative number')
    }
    const cur = this._services.get(service) || { remaining: 0, total: 0 }
    cur.remaining += amount
    cur.total += amount
    this._services.set(service, cur)
    this._stats.allocated++
    this.emit('allocate', { service, tokens: amount, remaining: cur.remaining })
    return cur.remaining
  }

  consume (service, n = 1) {
    assertNonEmpty(service, 'service')
    const amount = Number(n)
    if (!Number.isFinite(amount) || amount < 0) {
      throw new Error('n must be a non-negative number')
    }
    const cur = this._services.get(service)
    if (!cur || cur.remaining < amount) {
      this._stats.rejected++
      this.emit('reject', { service, requested: amount, remaining: cur ? cur.remaining : 0 })
      return false
    }
    cur.remaining -= amount
    this._stats.consumed++
    this.emit('consume', { service, n: amount, remaining: cur.remaining })
    return true
  }

  remaining (service) {
    assertNonEmpty(service, 'service')
    const cur = this._services.get(service)
    return cur ? cur.remaining : 0
  }

  services () {
    return [...this._services.keys()].sort()
  }

  snapshot (service) {
    const cur = this._services.get(service)
    if (!cur) return null
    return { service, remaining: cur.remaining, total: cur.total, used: cur.total - cur.remaining }
  }

  reset (service) {
    if (service) {
      this._services.delete(service)
      return true
    }
    this._services.clear()
    return true
  }

  getStats () {
    return {
      ...this._stats,
      services: this._services.size,
      protocol: PROTOCOL
    }
  }

  async ready () { return this }

  async close () {
    this._services.clear()
    this.emit('closed')
  }
}

module.exports = { HyperP2PSlaBudget, PROTOCOL }