core/packages/runtime-core/src/components/BaseTransition.ts

import {
  getCurrentInstance,
  SetupContext,
  ComponentInternalInstance
} from '../component'
import {
  cloneVNode,
  Comment,
  isSameVNodeType,
  VNode,
  VNodeArrayChildren,
  Fragment
} from '../vnode'
import { warn } from '../warning'
import { isKeepAlive } from './KeepAlive'
import { toRaw } from '@vue/reactivity'
import { callWithAsyncErrorHandling, ErrorCodes } from '../errorHandling'
import { ShapeFlags, PatchFlags } from '@vue/shared'
import { onBeforeUnmount, onMounted } from '../apiLifecycle'
import { RendererElement } from '../renderer'

export interface BaseTransitionProps<HostElement = RendererElement> {
  mode?: 'in-out' | 'out-in' | 'default'
  appear?: boolean

  // If true, indicates this is a transition that doesn't actually insert/remove
  // the element, but toggles the show / hidden status instead.
  // The transition hooks are injected, but will be skipped by the renderer.
  // Instead, a custom directive can control the transition by calling the
  // injected hooks (e.g. v-show).
  persisted?: boolean

  // Hooks. Using camel case for easier usage in render functions & JSX.
  // In templates these can be written as @before-enter="xxx" as prop names
  // are camelized.
  onBeforeEnter?: (el: HostElement) => void
  onEnter?: (el: HostElement, done: () => void) => void
  onAfterEnter?: (el: HostElement) => void
  onEnterCancelled?: (el: HostElement) => void
  // leave
  onBeforeLeave?: (el: HostElement) => void
  onLeave?: (el: HostElement, done: () => void) => void
  onAfterLeave?: (el: HostElement) => void
  onLeaveCancelled?: (el: HostElement) => void // only fired in persisted mode
  // appear
  onBeforeAppear?: (el: HostElement) => void
  onAppear?: (el: HostElement, done: () => void) => void
  onAfterAppear?: (el: HostElement) => void
  onAppearCancelled?: (el: HostElement) => void
}

export interface TransitionHooks<
  HostElement extends RendererElement = RendererElement
> {
  persisted: boolean
  beforeEnter(el: HostElement): void
  enter(el: HostElement): void
  leave(el: HostElement, remove: () => void): void
  afterLeave?(): void
  delayLeave?(
    el: HostElement,
    earlyRemove: () => void,
    delayedLeave: () => void
  ): void
  delayedLeave?(): void
}

type TransitionHookCaller = (
  hook: ((el: any) => void) | undefined,
  args?: any[]
) => void

export type PendingCallback = (cancelled?: boolean) => void

export interface TransitionState {
  isMounted: boolean
  isLeaving: boolean
  isUnmounting: boolean
  // Track pending leave callbacks for children of the same key.
  // This is used to force remove leaving a child when a new copy is entering.
  leavingVNodes: Map<any, Record<string, VNode>>
}

export interface TransitionElement {
  // in persisted mode (e.g. v-show), the same element is toggled, so the
  // pending enter/leave callbacks may need to be cancelled if the state is toggled
  // before it finishes.
  _enterCb?: PendingCallback
  _leaveCb?: PendingCallback
}

export function useTransitionState(): TransitionState {
  const state: TransitionState = {
    isMounted: false,
    isLeaving: false,
    isUnmounting: false,
    leavingVNodes: new Map()
  }
  onMounted(() => {
    state.isMounted = true
  })
  onBeforeUnmount(() => {
    state.isUnmounting = true
  })
  return state
}

const TransitionHookValidator = [Function, Array]

const BaseTransitionImpl = {
  name: `BaseTransition`,

  props: {
    mode: String,
    appear: Boolean,
    persisted: Boolean,
    // enter
    onBeforeEnter: TransitionHookValidator,
    onEnter: TransitionHookValidator,
    onAfterEnter: TransitionHookValidator,
    onEnterCancelled: TransitionHookValidator,
    // leave
    onBeforeLeave: TransitionHookValidator,
    onLeave: TransitionHookValidator,
    onAfterLeave: TransitionHookValidator,
    onLeaveCancelled: TransitionHookValidator,
    // appear
    onBeforeAppear: TransitionHookValidator,
    onAppear: TransitionHookValidator,
    onAfterAppear: TransitionHookValidator,
    onAppearCancelled: TransitionHookValidator
  },

  setup(props: BaseTransitionProps, { slots }: SetupContext) {
    const instance = getCurrentInstance()!
    const state = useTransitionState()

    let prevTransitionKey: any

    return () => {
      const children =
        slots.default && getTransitionRawChildren(slots.default(), true)
      if (!children || !children.length) {
        return
      }

      // warn multiple elements
      if (__DEV__ && children.length > 1) {
        warn(
          '<transition> can only be used on a single element or component. Use ' +
            '<transition-group> for lists.'
        )
      }

      // there's no need to track reactivity for these props so use the raw
      // props for a bit better perf
      const rawProps = toRaw(props)
      const { mode } = rawProps
      // check mode
      if (__DEV__ && mode && !['in-out', 'out-in', 'default'].includes(mode)) {
        warn(`invalid <transition> mode: ${mode}`)
      }

      // at this point children has a guaranteed length of 1.
      const child = children[0]
      if (state.isLeaving) {
        return emptyPlaceholder(child)
      }

      // in the case of <transition><keep-alive/></transition>, we need to
      // compare the type of the kept-alive children.
      const innerChild = getKeepAliveChild(child)
      if (!innerChild) {
        return emptyPlaceholder(child)
      }

      const enterHooks = (innerChild.transition = resolveTransitionHooks(
        innerChild,
        rawProps,
        state,
        instance
      ))

      const oldChild = instance.subTree
      const oldInnerChild = oldChild && getKeepAliveChild(oldChild)

      let transitionKeyChanged = false
      const { getTransitionKey } = innerChild.type as any
      if (getTransitionKey) {
        const key = getTransitionKey()
        if (prevTransitionKey === undefined) {
          prevTransitionKey = key
        } else if (key !== prevTransitionKey) {
          prevTransitionKey = key
          transitionKeyChanged = true
        }
      }

      // handle mode
      if (
        oldInnerChild &&
        oldInnerChild.type !== Comment &&
        (!isSameVNodeType(innerChild, oldInnerChild) || transitionKeyChanged)
      ) {
        const leavingHooks = resolveTransitionHooks(
          oldInnerChild,
          rawProps,
          state,
          instance
        )
        // update old tree's hooks in case of dynamic transition
        setTransitionHooks(oldInnerChild, leavingHooks)
        // switching between different views
        if (mode === 'out-in') {
          state.isLeaving = true
          // return placeholder node and queue update when leave finishes
          leavingHooks.afterLeave = () => {
            state.isLeaving = false
            instance.update()
          }
          return emptyPlaceholder(child)
        } else if (mode === 'in-out') {
          leavingHooks.delayLeave = (
            el: TransitionElement,
            earlyRemove,
            delayedLeave
          ) => {
            const leavingVNodesCache = getLeavingNodesForType(
              state,
              oldInnerChild
            )
            leavingVNodesCache[String(oldInnerChild.key)] = oldInnerChild
            // early removal callback
            el._leaveCb = () => {
              earlyRemove()
              el._leaveCb = undefined
              delete enterHooks.delayedLeave
            }
            enterHooks.delayedLeave = delayedLeave
          }
        }
      }

      return child
    }
  }
}

// export the public type for h/tsx inference
// also to avoid inline import() in generated d.ts files
export const BaseTransition = (BaseTransitionImpl as any) as {
  new (): {
    $props: BaseTransitionProps<any>
  }
}

function getLeavingNodesForType(
  state: TransitionState,
  vnode: VNode
): Record<string, VNode> {
  const { leavingVNodes } = state
  let leavingVNodesCache = leavingVNodes.get(vnode.type)!
  if (!leavingVNodesCache) {
    leavingVNodesCache = Object.create(null)
    leavingVNodes.set(vnode.type, leavingVNodesCache)
  }
  return leavingVNodesCache
}

// The transition hooks are attached to the vnode as vnode.transition
// and will be called at appropriate timing in the renderer.
export function resolveTransitionHooks(
  vnode: VNode,
  {
    appear,
    persisted = false,
    onBeforeEnter,
    onEnter,
    onAfterEnter,
    onEnterCancelled,
    onBeforeLeave,
    onLeave,
    onAfterLeave,
    onLeaveCancelled,
    onBeforeAppear,
    onAppear,
    onAfterAppear,
    onAppearCancelled
  }: BaseTransitionProps<any>,
  state: TransitionState,
  instance: ComponentInternalInstance
): TransitionHooks {
  const key = String(vnode.key)
  const leavingVNodesCache = getLeavingNodesForType(state, vnode)

  const callHook: TransitionHookCaller = (hook, args) => {
    hook &&
      callWithAsyncErrorHandling(
        hook,
        instance,
        ErrorCodes.TRANSITION_HOOK,
        args
      )
  }

  const hooks: TransitionHooks<TransitionElement> = {
    persisted,
    beforeEnter(el) {
      let hook = onBeforeEnter
      if (!state.isMounted) {
        if (appear) {
          hook = onBeforeAppear || onBeforeEnter
        } else {
          return
        }
      }
      // for same element (v-show)
      if (el._leaveCb) {
        el._leaveCb(true /* cancelled */)
      }
      // for toggled element with same key (v-if)
      const leavingVNode = leavingVNodesCache[key]
      if (
        leavingVNode &&
        isSameVNodeType(vnode, leavingVNode) &&
        leavingVNode.el!._leaveCb
      ) {
        // force early removal (not cancelled)
        leavingVNode.el!._leaveCb()
      }
      callHook(hook, [el])
    },

    enter(el) {
      let hook = onEnter
      let afterHook = onAfterEnter
      let cancelHook = onEnterCancelled
      if (!state.isMounted) {
        if (appear) {
          hook = onAppear || onEnter
          afterHook = onAfterAppear || onAfterEnter
          cancelHook = onAppearCancelled || onEnterCancelled
        } else {
          return
        }
      }
      let called = false
      const done = (el._enterCb = (cancelled?) => {
        if (called) return
        called = true
        if (cancelled) {
          callHook(cancelHook, [el])
        } else {
          callHook(afterHook, [el])
        }
        if (hooks.delayedLeave) {
          hooks.delayedLeave()
        }
        el._enterCb = undefined
      })
      if (hook) {
        hook(el, done)
        if (hook.length <= 1) {
          done()
        }
      } else {
        done()
      }
    },

    leave(el, remove) {
      const key = String(vnode.key)
      if (el._enterCb) {
        el._enterCb(true /* cancelled */)
      }
      if (state.isUnmounting) {
        return remove()
      }
      callHook(onBeforeLeave, [el])
      let called = false
      const done = (el._leaveCb = (cancelled?) => {
        if (called) return
        called = true
        remove()
        if (cancelled) {
          callHook(onLeaveCancelled, [el])
        } else {
          callHook(onAfterLeave, [el])
        }
        el._leaveCb = undefined
        if (leavingVNodesCache[key] === vnode) {
          delete leavingVNodesCache[key]
        }
      })
      leavingVNodesCache[key] = vnode
      if (onLeave) {
        onLeave(el, done)
        if (onLeave.length <= 1) {
          done()
        }
      } else {
        done()
      }
    }
  }

  return hooks
}

// the placeholder really only handles one special case: KeepAlive
// in the case of a KeepAlive in a leave phase we need to return a KeepAlive
// placeholder with empty content to avoid the KeepAlive instance from being
// unmounted.
function emptyPlaceholder(vnode: VNode): VNode | undefined {
  if (isKeepAlive(vnode)) {
    vnode = cloneVNode(vnode)
    vnode.children = null
    return vnode
  }
}

function getKeepAliveChild(vnode: VNode): VNode | undefined {
  return isKeepAlive(vnode)
    ? vnode.children
      ? ((vnode.children as VNodeArrayChildren)[0] as VNode)
      : undefined
    : vnode
}

export function setTransitionHooks(vnode: VNode, hooks: TransitionHooks) {
  if (vnode.shapeFlag & ShapeFlags.COMPONENT && vnode.component) {
    setTransitionHooks(vnode.component.subTree, hooks)
  } else {
    vnode.transition = hooks
  }
}

export function getTransitionRawChildren(
  children: VNode[],
  keepComment: boolean = false
): VNode[] {
  let ret: VNode[] = []
  let keyedFragmentCount = 0
  for (let i = 0; i < children.length; i++) {
    const child = children[i]
    // handle fragment children case, e.g. v-for
    if (child.type === Fragment) {
      if (child.patchFlag & PatchFlags.KEYED_FRAGMENT) keyedFragmentCount++
      ret = ret.concat(
        getTransitionRawChildren(child.children as VNode[], keepComment)
      )
    }
    // comment placeholders should be skipped, e.g. v-if
    else if (keepComment || child.type !== Comment) {
      ret.push(child)
    }
  }
  // #1126 if a transition children list contains multiple sub fragments, these
  // fragments will be merged into a flat children array. Since each v-for
  // fragment may contain different static bindings inside, we need to de-top
  // these children to force full diffs to ensure correct behavior.
  if (keyedFragmentCount > 1) {
    for (let i = 0; i < ret.length; i++) {
      ret[i].patchFlag = PatchFlags.BAIL
    }
  }
  return ret
}