import {
  ComponentNode,
  TransformContext,
  buildSlots,
  createFunctionExpression,
  FunctionExpression,
  TemplateChildNode,
  createCallExpression,
  SlotsExpression
} from '@vue/compiler-dom'
import {
  SSRTransformContext,
  processChildrenAsStatement
} from '../ssrCodegenTransform'
import { SSR_RENDER_SUSPENSE } from '../runtimeHelpers'

const wipMap = new WeakMap<ComponentNode, WIPEntry>()

interface WIPEntry {
  slotsExp: SlotsExpression
  wipSlots: Array<{
    fn: FunctionExpression
    children: TemplateChildNode[]
  }>
}

// phase 1
export function ssrTransformSuspense(
  node: ComponentNode,
  context: TransformContext
) {
  return () => {
    if (node.children.length) {
      const wipEntry: WIPEntry = {
        slotsExp: null as any,
        wipSlots: []
      }
      wipMap.set(node, wipEntry)
      wipEntry.slotsExp = buildSlots(node, context, (_props, children, loc) => {
        const fn = createFunctionExpression(
          [],
          undefined, // no return, assign body later
          true, // newline
          false, // suspense slots are not treated as normal slots
          loc
        )
        wipEntry.wipSlots.push({
          fn,
          children
        })
        return fn
      }).slots
    }
  }
}

// phase 2
export function ssrProcessSuspense(
  node: ComponentNode,
  context: SSRTransformContext
) {
  // complete wip slots with ssr code
  const wipEntry = wipMap.get(node)
  if (!wipEntry) {
    return
  }
  const { slotsExp, wipSlots } = wipEntry
  for (let i = 0; i < wipSlots.length; i++) {
    const { fn, children } = wipSlots[i]
    fn.body = processChildrenAsStatement(children, context)
  }
  // _push(ssrRenderSuspense(slots))
  context.pushStatement(
    createCallExpression(context.helper(SSR_RENDER_SUSPENSE), [
      `_push`,
      slotsExp
    ])
  )
}