import { useStore } from '@nanostores/react'
import { atom } from 'nanostores'
import { useCallback, useEffect, useMemo } from 'react'

import { clearProjectDirCache, readProjectDir } from './ipc'

export interface TreeNode {
  /** Absolute filesystem path. Doubles as react-arborist node id. */
  id: string
  name: string
  /** Drives arborist's leaf-vs-expandable decision via childrenAccessor. */
  isDirectory: boolean
  /** `undefined` = directory, children not yet loaded. `[]` = loaded empty. */
  children?: TreeNode[]
  /** True while a readDir for this folder is in flight. */
  loading?: boolean
  /** Last error code from readDir (e.g. EACCES). Cleared on next successful load. */
  error?: string
}

const PLACEHOLDER_ID = '__loading__'

function makeNode(path: string, name: string, isDirectory: boolean): TreeNode {
  return { id: path, isDirectory, name }
}

function patchNode(nodes: TreeNode[] | undefined | null, id: string, patch: (n: TreeNode) => TreeNode): TreeNode[] {
  if (!nodes) {
    return []
  }

  return nodes.map(n => {
    if (n.id === id) {
      return patch(n)
    }

    if (n.children && n.children.length > 0) {
      return { ...n, children: patchNode(n.children, id, patch) }
    }

    return n
  })
}

function placeholderChild(parentId: string): TreeNode {
  return { id: `${parentId}::${PLACEHOLDER_ID}`, isDirectory: false, name: 'Loading…' }
}

export interface UseProjectTreeResult {
  data: TreeNode[]
  openState: Record<string, boolean>
  rootError: string | null
  rootLoading: boolean
  loadChildren: (id: string) => Promise<void>
  refreshRoot: () => Promise<void>
  setNodeOpen: (id: string, open: boolean) => void
}

interface ProjectTreeState {
  cwd: string
  data: TreeNode[]
  loaded: boolean
  openState: Record<string, boolean>
  requestId: number
  rootError: string | null
  rootLoading: boolean
}

const initialState: ProjectTreeState = {
  cwd: '',
  data: [],
  loaded: false,
  openState: {},
  requestId: 0,
  rootError: null,
  rootLoading: false
}

const inflight = new Set<string>()
const $projectTree = atom<ProjectTreeState>(initialState)
let nextRootRequestId = 0

function setProjectTree(updater: (current: ProjectTreeState) => ProjectTreeState) {
  $projectTree.set(updater($projectTree.get()))
}

function clearProjectTree() {
  nextRootRequestId += 1
  inflight.clear()
  $projectTree.set({ ...initialState, requestId: nextRootRequestId })
}

async function loadRoot(cwd: string, { force = false }: { force?: boolean } = {}) {
  if (!cwd) {
    clearProjectTree()

    return
  }

  const current = $projectTree.get()

  if (!force && current.cwd === cwd && (current.loaded || current.rootLoading)) {
    return
  }

  const requestId = nextRootRequestId + 1
  nextRootRequestId = requestId
  inflight.clear()

  if (force || current.cwd !== cwd) {
    clearProjectDirCache(cwd)
  }

  $projectTree.set({
    cwd,
    data: [],
    loaded: false,
    openState: current.cwd === cwd ? current.openState : {},
    requestId,
    rootError: null,
    rootLoading: true
  })

  const { entries, error } = await readProjectDir(cwd, cwd)

  setProjectTree(latest => {
    if (latest.cwd !== cwd || latest.requestId !== requestId) {
      return latest
    }

    return {
      ...latest,
      data: error ? [] : entries.map(e => makeNode(e.path, e.name, e.isDirectory)),
      loaded: true,
      rootError: error || null,
      rootLoading: false
    }
  })
}

export function resetProjectTreeState() {
  clearProjectTree()
  clearProjectDirCache()
}

/**
 * Lazy-loads a directory tree rooted at `cwd`. Children are fetched on first
 * expand and cached in this feature-owned atom so unrelated chat rerenders or
 * remounts cannot reset the browser. A placeholder leaf renders so the
 * disclosure caret shows for unloaded folders. `refreshRoot` invalidates the
 * whole tree (used after cwd change or manual refresh).
 */
export function useProjectTree(cwd: string): UseProjectTreeResult {
  const state = useStore($projectTree)

  const refreshRoot = useCallback(() => loadRoot(cwd, { force: true }), [cwd])

  const setNodeOpen = useCallback(
    (id: string, open: boolean) => {
      setProjectTree(current => {
        if (current.cwd !== cwd || current.openState[id] === open) {
          return current
        }

        return {
          ...current,
          openState: {
            ...current.openState,
            [id]: open
          }
        }
      })
    },
    [cwd]
  )

  const loadChildren = useCallback(
    async (id: string) => {
      if (!cwd || inflight.has(id)) {
        return
      }

      inflight.add(id)

      setProjectTree(current => {
        if (current.cwd !== cwd) {
          return current
        }

        return {
          ...current,
          data: patchNode(current.data, id, n => ({ ...n, loading: true, children: [placeholderChild(n.id)] }))
        }
      })

      const { entries, error } = await readProjectDir(id, cwd)

      inflight.delete(id)

      setProjectTree(current => {
        if (current.cwd !== cwd) {
          return current
        }

        return {
          ...current,
          data: patchNode(current.data, id, n => ({
            ...n,
            loading: false,
            error: error || undefined,
            children: error ? [] : entries.map(e => makeNode(e.path, e.name, e.isDirectory))
          }))
        }
      })
    },
    [cwd]
  )

  useEffect(() => {
    void loadRoot(cwd)
  }, [cwd])

  return useMemo(
    () => ({
      data: state.cwd === cwd ? state.data : [],
      loadChildren,
      openState: state.cwd === cwd ? state.openState : {},
      refreshRoot,
      rootError: state.cwd === cwd ? state.rootError : null,
      rootLoading: state.cwd === cwd ? state.rootLoading : false,
      setNodeOpen
    }),
    [
      cwd,
      loadChildren,
      refreshRoot,
      setNodeOpen,
      state.cwd,
      state.data,
      state.openState,
      state.rootError,
      state.rootLoading
    ]
  )
}