import {
  createContext,
  useContext,
  useEffect,
  FC,
  useCallback,
  useMemo,
  useState,
  useRef,
} from 'react'
import { useIdeReactContext } from '@/features/ide-react/context/ide-react-context'
import { useConnectionContext } from '@/features/ide-react/context/connection-context'
import { useEditorManagerContext } from '@/features/ide-react/context/editor-manager-context'
import _ from 'lodash'
import { getJSON, postJSON } from '@/infrastructure/fetch-json'
import { useOnlineUsersContext } from '@/features/ide-react/context/online-users-context'
import { useEditorContext } from '@/shared/context/editor-context'
import { useIdeContext } from '@/shared/context/ide-context'
import useSocketListener from '@/features/ide-react/hooks/use-socket-listener'
import useEventListener from '@/shared/hooks/use-event-listener'

type DocumentMetadata = {
  labels: string[]
  packages: Record<string, any>
}

type DocumentsMetadata = Record<string, DocumentMetadata>

type MetadataContextValue = {
  metadata: {
    state: {
      documents: DocumentsMetadata
    }
    getAllLabels: () => DocumentMetadata['labels']
    getAllPackages: () => DocumentMetadata['packages']
  }
}

type DocMetadataResponse = { docId: string; meta: DocumentMetadata }

const MetadataContext = createContext<MetadataContextValue | undefined>(
  undefined
)

export const MetadataProvider: FC = ({ children }) => {
  const ide = useIdeContext()
  const { eventEmitter, projectId } = useIdeReactContext()
  const { socket } = useConnectionContext()
  const { onlineUsersCount } = useOnlineUsersContext()
  const { permissionsLevel } = useEditorContext()
  const { currentDocument } = useEditorManagerContext()

  const [documents, setDocuments] = useState<DocumentsMetadata>({})

  const debouncerRef = useRef<Map<string, number>>(new Map()) // DocId => Timeout

  useEffect(() => {
    eventEmitter.on('entity:deleted', entity => {
      if (entity.type === 'doc') {
        setDocuments(documents => _.omit(documents, entity.id))
      }
    })
  }, [eventEmitter])

  useEffect(() => {
    window.dispatchEvent(
      new CustomEvent('project:metadata', { detail: documents })
    )
  }, [documents])

  const onBroadcastDocMeta = useCallback((data: DocMetadataResponse) => {
    const { docId, meta } = data
    if (docId != null && meta != null) {
      setDocuments(documents => ({ ...documents, [docId]: meta }))
    }
  }, [])

  const getAllLabels = useCallback(
    () =>
      _.flattenDeep(
        Array.from(Object.values(documents)).map(meta => meta.labels)
      ),
    [documents]
  )

  const getAllPackages = useCallback(() => {
    const packageCommandMapping: Record<string, any> = {}
    for (const meta of Object.values(documents)) {
      for (const [packageName, commandSnippets] of Object.entries(
        meta.packages
      )) {
        packageCommandMapping[packageName] = commandSnippets
      }
    }
    return packageCommandMapping
  }, [documents])

  const loadProjectMetaFromServer = useCallback(() => {
    getJSON(`/project/${projectId}/metadata`).then(
      (response: { projectMeta: DocumentsMetadata }) => {
        const { projectMeta } = response
        if (projectMeta) {
          setDocuments(projectMeta)
        }
      }
    )
  }, [projectId])

  const loadDocMetaFromServer = useCallback(
    (docId: string) => {
      // Don't broadcast metadata when there are no other users in the
      // project.
      const broadcast = onlineUsersCount > 0
      postJSON(`/project/${projectId}/doc/${docId}/metadata`, {
        body: {
          broadcast,
        },
      }).then((response: DocMetadataResponse) => {
        if (!broadcast && response) {
          // handle the POST response like a broadcast event when there are no
          // other users in the project.
          onBroadcastDocMeta(response)
        }
      })
    },
    [onBroadcastDocMeta, onlineUsersCount, projectId]
  )

  const scheduleLoadDocMetaFromServer = useCallback(
    (docId: string) => {
      if (permissionsLevel === 'readOnly') {
        // The POST request is blocked for users without write permission.
        // The user will not be able to consume the metadata for edits anyway.
        return
      }
      // Debounce loading labels with a timeout
      const existingTimeout = debouncerRef.current.get(docId)

      if (existingTimeout != null) {
        window.clearTimeout(existingTimeout)
        debouncerRef.current.delete(docId)
      }

      debouncerRef.current.set(
        docId,
        window.setTimeout(() => {
          // TODO: wait for the document to be saved?
          loadDocMetaFromServer(docId)
          debouncerRef.current.delete(docId)
        }, 2000)
      )
    },
    [loadDocMetaFromServer, permissionsLevel]
  )

  const handleBroadcastDocMeta = useCallback(
    (data: DocMetadataResponse) => {
      onBroadcastDocMeta(data)
    },
    [onBroadcastDocMeta]
  )

  useSocketListener(socket, 'broadcastDocMeta', handleBroadcastDocMeta)

  const handleMetadataOutdated = useCallback(() => {
    if (currentDocument) {
      scheduleLoadDocMetaFromServer(currentDocument.doc_id)
    }
  }, [currentDocument, scheduleLoadDocMetaFromServer])

  useEventListener('editor:metadata-outdated', handleMetadataOutdated)

  useEffect(() => {
    eventEmitter.once('project:joined', ({ project }) => {
      if (project.deletedByExternalDataSource) {
        // TODO: MIGRATION: Show generic message modal here
        /*
        ide.showGenericMessageModal(
          'Project Renamed or Deleted',
          `\
This project has either been renamed or deleted by an external data source such as Dropbox.
We don't want to delete your data on Overleaf, so this project still contains your history and collaborators.
If the project has been renamed please look in your project list for a new project under the new name.\
`
        )
*/
      }
      window.setTimeout(() => {
        if (permissionsLevel !== 'readOnly') {
          loadProjectMetaFromServer()
        }
      }, 200)
    })
  }, [eventEmitter, loadProjectMetaFromServer, permissionsLevel])

  const value = useMemo<MetadataContextValue>(
    () => ({
      metadata: {
        state: { documents },
        getAllLabels,
        getAllPackages,
      },
    }),
    [documents, getAllLabels, getAllPackages]
  )

  // Expose metadataManager via ide object because useCodeMirrorScope relies on
  // it, for now
  ide.metadataManager = value

  return (
    <MetadataContext.Provider value={value}>
      {children}
    </MetadataContext.Provider>
  )
}

export function useMetadataContext(): MetadataContextValue {
  const context = useContext(MetadataContext)

  if (!context) {
    throw new Error(
      'useMetadataContext is only available inside MetadataProvider'
    )
  }

  return context
}