/**
 * Copyright 2018-present Facebook.
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 * @format
 */
import { StyleSheet } from './sheet'

type BaseRules = {
  [key: string]: string | number
}

export type StyleTracker = Map<
  string,
  {
    displayName?: string
    namespace: string
    rules: BaseRules
    // we can compile it later and use it for speed
    // only using in the motion View.tsx stuff for now
    styleObject?: Object
    selector: string
    style: string
    className: string
  }
>

export class GarbageCollector {
  // used to keep track of what classes are actively in use
  usedClasses = new Map<string, number>()
  // classes to be removed, we put this in a queue and perform it in bulk rather than straight away
  // since by the time the next tick happens this style could have been reinserted
  classRemovalQueue = new Set<string>()
  // uid registered queue
  activeUids = new Set<string>()

  constructor(sheet: StyleSheet, tracker: StyleTracker) {
    this.sheet = sheet
    this.tracker = tracker
  }

  tracker: StyleTracker
  sheet: StyleSheet
  garbageTimer?: any

  hasQueuedCollection(): boolean {
    return Boolean(this.garbageTimer)
  }

  getReferenceCount(key: string): number {
    return this.usedClasses.get(key) || 0
  }

  // component has been mounted so make sure it's being depended on
  registerClassUse = (name: string) => {
    const count = this.usedClasses.get(name) || 0
    this.usedClasses.set(name, count + 1)
    if (this.classRemovalQueue.has(name)) {
      this.classRemovalQueue.delete(name)
      if (this.classRemovalQueue.size === 0) {
        this.haltGarbage()
      }
    }
  }

  // component has been unmounted so remove it's dependencies
  deregisterClassUse = (name: string) => {
    let count = this.usedClasses.get(name)
    if (count == null) {
      return
    }
    count--
    this.usedClasses.set(name, count)
    if (count === 0) {
      this.classRemovalQueue.add(name)
      this.scheduleGarbage()
    }
  }

  scheduleGarbage = () => {
    if (this.garbageTimer != null) {
      return
    }
    this.garbageTimer = setTimeout(() => {
      window['requestIdleCallback'](() => {
        this.collectGarbage()
      })
    }, 10000)
  }

  haltGarbage() {
    if (this.garbageTimer) {
      clearTimeout(this.garbageTimer)
      this.garbageTimer = undefined
    }
  }

  getCollectionQueue(): string[] {
    return Array.from(this.classRemovalQueue)
  }

  collectGarbage() {
    this.haltGarbage()
    for (const name of this.classRemovalQueue) {
      const trackerInfo = this.tracker.get(name)
      if (!trackerInfo) throw 'trying to remove unknown class'
      if (trackerInfo) {
        this.sheet.delete(name)
        this.tracker.delete(name)
        this.usedClasses.delete(name)
      }
    }
    this.classRemovalQueue.clear()
  }

  flush() {
    this.haltGarbage()
    this.classRemovalQueue.clear()
    this.usedClasses.clear()
  }
}