core/packages/reactivity/src/effect.ts

import { TrackOpTypes, TriggerOpTypes } from './operations'
import { extend, isArray, isIntegerKey, isMap } from '@vue/shared'
import { EffectScope, recordEffectScope } from './effectScope'
import {
  createDep,
  Dep,
  finalizeDepMarkers,
  initDepMarkers,
  newTracked,
  wasTracked
} from './Dep'

// The main WeakMap that stores {target -> key -> dep} connections.
// Conceptually, it's easier to think of a dependency as a Dep class
// which maintains a Set of subscribers, but we simply store them as
// raw Sets to reduce memory overhead.
type KeyToDepMap = Map<any, Dep>
const targetMap = new WeakMap<any, KeyToDepMap>()

// The number of effects currently being tracked recursively.
let effectTrackDepth = 0

export let trackOpBit = 1

/**
 * The bitwise track markers support at most 30 levels op recursion.
 * This value is chosen to enable modern JS engines to use a SMI on all platforms.
 * When recursion depth is greater, fall back to using a full cleanup.
 */
const maxMarkerBits = 30

export type EffectScheduler = () => void

export type DebuggerEvent = {
  effect: ReactiveEffect
} & DebuggerEventExtraInfo

export type DebuggerEventExtraInfo = {
  target: object
  type: TrackOpTypes | TriggerOpTypes
  key: any
  newValue?: any
  oldValue?: any
  oldTarget?: Map<any, any> | Set<any>
}

const effectStack: ReactiveEffect[] = []
let activeEffect: ReactiveEffect | undefined

export const ITERATE_KEY = Symbol(__DEV__ ? 'iterate' : '')
export const MAP_KEY_ITERATE_KEY = Symbol(__DEV__ ? 'Map key iterate' : '')

export class ReactiveEffect<T = any> {
  active = true
  deps: Dep[] = []

  // can be attached after creation
  onStop?: () => void
  // dev only
  onTrack?: (event: DebuggerEvent) => void
  // dev only
  onTrigger?: (event: DebuggerEvent) => void

  constructor(
    public fn: () => T,
    public scheduler: EffectScheduler | null = null,
    scope?: EffectScope | null,
    // allow recursive self-invocation
    public allowRecurse = false
  ) {
    recordEffectScope(this, scope)
  }

  run() {
    if (!this.active) {
      return this.fn()
    }
    if (!effectStack.includes(this)) {
      try {
        effectStack.push((activeEffect = this))
        enableTracking()

        trackOpBit = 1 << ++effectTrackDepth

        if (effectTrackDepth <= maxMarkerBits) {
          initDepMarkers(this)
        } else {
          cleanupEffect(this)
        }
        return this.fn()
      } finally {
        if (effectTrackDepth <= maxMarkerBits) {
          finalizeDepMarkers(this)
        }

        trackOpBit = 1 << --effectTrackDepth

        resetTracking()
        effectStack.pop()
        const n = effectStack.length
        activeEffect = n > 0 ? effectStack[n - 1] : undefined
      }
    }
  }

  stop() {
    if (this.active) {
      cleanupEffect(this)
      if (this.onStop) {
        this.onStop()
      }
      this.active = false
    }
  }
}

function cleanupEffect(effect: ReactiveEffect) {
  const { deps } = effect
  if (deps.length) {
    for (let i = 0; i < deps.length; i++) {
      deps[i].delete(effect)
    }
    deps.length = 0
  }
}

export interface ReactiveEffectOptions {
  lazy?: boolean
  scheduler?: EffectScheduler
  scope?: EffectScope
  allowRecurse?: boolean
  onStop?: () => void
  onTrack?: (event: DebuggerEvent) => void
  onTrigger?: (event: DebuggerEvent) => void
}

export interface ReactiveEffectRunner<T = any> {
  (): T
  effect: ReactiveEffect
}

export function effect<T = any>(
  fn: () => T,
  options?: ReactiveEffectOptions
): ReactiveEffectRunner {
  if ((fn as ReactiveEffectRunner).effect) {
    fn = (fn as ReactiveEffectRunner).effect.fn
  }

  const _effect = new ReactiveEffect(fn)
  if (options) {
    extend(_effect, options)
    if (options.scope) recordEffectScope(_effect, options.scope)
  }
  if (!options || !options.lazy) {
    _effect.run()
  }
  const runner = _effect.run.bind(_effect) as ReactiveEffectRunner
  runner.effect = _effect
  return runner
}

export function stop(runner: ReactiveEffectRunner) {
  runner.effect.stop()
}

let shouldTrack = true
const trackStack: boolean[] = []

export function pauseTracking() {
  trackStack.push(shouldTrack)
  shouldTrack = false
}

export function enableTracking() {
  trackStack.push(shouldTrack)
  shouldTrack = true
}

export function resetTracking() {
  const last = trackStack.pop()
  shouldTrack = last === undefined ? true : last
}

export function track(target: object, type: TrackOpTypes, key: unknown) {
  if (!isTracking()) {
    return
  }
  let depsMap = targetMap.get(target)
  if (!depsMap) {
    targetMap.set(target, (depsMap = new Map()))
  }
  let dep = depsMap.get(key)
  if (!dep) {
    depsMap.set(key, (dep = createDep()))
  }

  const eventInfo = __DEV__
    ? { effect: activeEffect, target, type, key }
    : undefined

  trackEffects(dep, eventInfo)
}

export function isTracking() {
  return shouldTrack && activeEffect !== undefined
}

export function trackEffects(
  dep: Dep,
  debuggerEventExtraInfo?: DebuggerEventExtraInfo
) {
  let shouldTrack = false
  if (effectTrackDepth <= maxMarkerBits) {
    if (!newTracked(dep)) {
      dep.n |= trackOpBit // set newly tracked
      shouldTrack = !wasTracked(dep)
    }
  } else {
    // Full cleanup mode.
    shouldTrack = !dep.has(activeEffect!)
  }

  if (shouldTrack) {
    dep.add(activeEffect!)
    activeEffect!.deps.push(dep)
    if (__DEV__ && activeEffect!.onTrack) {
      activeEffect!.onTrack(
        Object.assign(
          {
            effect: activeEffect!
          },
          debuggerEventExtraInfo
        )
      )
    }
  }
}

export function trigger(
  target: object,
  type: TriggerOpTypes,
  key?: unknown,
  newValue?: unknown,
  oldValue?: unknown,
  oldTarget?: Map<unknown, unknown> | Set<unknown>
) {
  const depsMap = targetMap.get(target)
  if (!depsMap) {
    // never been tracked
    return
  }

  let deps: (Dep | undefined)[] = []
  if (type === TriggerOpTypes.CLEAR) {
    // collection being cleared
    // trigger all effects for target
    deps = [...depsMap.values()]
  } else if (key === 'length' && isArray(target)) {
    depsMap.forEach((dep, key) => {
      if (key === 'length' || key >= (newValue as number)) {
        deps.push(dep)
      }
    })
  } else {
    // schedule runs for SET | ADD | DELETE
    if (key !== void 0) {
      deps.push(depsMap.get(key))
    }

    // also run for iteration key on ADD | DELETE | Map.SET
    switch (type) {
      case TriggerOpTypes.ADD:
        if (!isArray(target)) {
          deps.push(depsMap.get(ITERATE_KEY))
          if (isMap(target)) {
            deps.push(depsMap.get(MAP_KEY_ITERATE_KEY))
          }
        } else if (isIntegerKey(key)) {
          // new index added to array -> length changes
          deps.push(depsMap.get('length'))
        }
        break
      case TriggerOpTypes.DELETE:
        if (!isArray(target)) {
          deps.push(depsMap.get(ITERATE_KEY))
          if (isMap(target)) {
            deps.push(depsMap.get(MAP_KEY_ITERATE_KEY))
          }
        }
        break
      case TriggerOpTypes.SET:
        if (isMap(target)) {
          deps.push(depsMap.get(ITERATE_KEY))
        }
        break
    }
  }

  const eventInfo = __DEV__
    ? { target, type, key, newValue, oldValue, oldTarget }
    : undefined

  if (deps.length === 1) {
    if (deps[0]) {
      triggerEffects(deps[0], eventInfo)
    }
  } else {
    const effects: ReactiveEffect[] = []
    for (const dep of deps) {
      if (dep) {
        effects.push(...dep)
      }
    }
    triggerEffects(createDep(effects), eventInfo)
  }
}

export function triggerEffects(
  dep: Dep,
  debuggerEventExtraInfo?: DebuggerEventExtraInfo
) {
  // spread into array for stabilization
  for (const effect of [...dep]) {
    if (effect !== activeEffect || effect.allowRecurse) {
      if (__DEV__ && effect.onTrigger) {
        effect.onTrigger(extend({ effect }, debuggerEventExtraInfo))
      }
      if (effect.scheduler) {
        effect.scheduler()
      } else {
        effect.run()
      }
    }
  }
}